Provided by: openvswitch-common_3.4.0-1_amd64 
NAME
ovs-fields - protocol header fields in OpenFlow and Open vSwitch
INTRODUCTION
This document aims to comprehensively document all of the fields, both standard and non-standard,
supported by OpenFlow or Open vSwitch, regardless of origin.
Fields
A field is a property of a packet. Most familiarly, data fields are fields that can be extracted from a
packet. Most data fields are copied directly from protocol headers, e.g. at layer 2, the Ethernet source
and destination addresses, or the VLAN ID; at layer 3, the IPv4 or IPv6 source and destination; and at
layer 4, the TCP or UDP ports. Other data fields are computed, e.g. ip_frag describes whether a packet is
a fragment but it is not copied directly from the IP header.
Data fields that are always present as a consequence of the basic networking technology in use are called
called root fields. Open vSwitch 2.7 and earlier considered Ethernet fields to be root fields, and this
remains the default mode of operation for Open vSwitch bridges. When a packet is received from a non-
Ethernet interfaces, such as a layer-3 LISP tunnel, Open vSwitch 2.7 and earlier force-fit the packet to
this Ethernet-centric point of view by pretending that an Ethernet header is present whose Ethernet type
that indicates the packet’s actual type (and whose source and destination addresses are all-zero).
Open vSwitch 2.8 and later implement the ``packet type-aware pipeline’’ concept introduced in OpenFlow
1.5. Such a pipeline does not have any root fields. Instead, a new metadata field, packet_type, indicates
the basic type of the packet, which can be Ethernet, IPv4, IPv6, or another type. For backward
compatibility, by default Open vSwitch 2.8 imitates the behavior of Open vSwitch 2.7 and earlier. Later
versions of Open vSwitch may change the default, and in the meantime controllers can turn off this legacy
behavior, on a port-by-port basis, by setting options:packet_type to ptap in the Interface table. This is
significant only for ports that can handle non-Ethernet packets, which is currently just LISP, VXLAN-GPE,
and GRE tunnel ports. See ovs-vwitchd.conf.db(5) for more information.
Non-root data fields are not always present. A packet contains ARP fields, for example, only when its
packet type is ARP or when it is an Ethernet packet whose Ethernet header indicates the Ethertype for
ARP, 0x0806. In this documentation, we say that a field is applicable when it is present in a packet, and
inapplicable when it is not. (These are not standard terms.) We refer to the conditions that determine
whether a field is applicable as prerequisites. Some VLAN-related fields are a special case: these fields
are always applicable for Ethernet packets, but have a designated value or bit that indicates whether a
VLAN header is present, with the remaining values or bits indicating the VLAN header’s content (if it is
present).
An inapplicable field does not have a value, not even a nominal ``value’’ such as all-zero-bits. In many
circumstances, OpenFlow and Open vSwitch allow references only to applicable fields. For example, one may
match (see Matching, below) a given field only if the match includes the field’s prerequisite, e.g.
matching an ARP field is only allowed if one also matches on Ethertype 0x0806 or the packet_type for ARP
in a packet type-aware bridge.
Sometimes a packet may contain multiple instances of a header. For example, a packet may contain multiple
VLAN or MPLS headers, and tunnels can cause any data field to recur. OpenFlow and Open vSwitch do not
address these cases uniformly. For VLAN and MPLS headers, only the outermost header is accessible, so
that inner headers may be accessed only by ``popping’’ (removing) the outer header. (Open vSwitch
supports only a single VLAN header in any case.) For tunnels, e.g. GRE or VXLAN, the outer header and
inner headers are treated as different data fields.
Many network protocols are built in layers as a stack of concatenated headers. Each header typically
contains a ``next type’’ field that indicates the type of the protocol header that follows, e.g. Ethernet
contains an Ethertype and IPv4 contains a IP protocol type. The exceptional cases, where protocols are
layered but an outer layer does not indicate the protocol type for the inner layer, or gives only an
ambiguous indication, are troublesome. An MPLS header, for example, only indicates whether another MPLS
header or some other protocol follows, and in the latter case the inner protocol must be known from the
context. In these exceptional cases, OpenFlow and Open vSwitch cannot provide insight into the inner
protocol data fields without additional context, and thus they treat all later data fields as
inapplicable until an OpenFlow action explicitly specifies what protocol follows. In the case of MPLS,
the OpenFlow ``pop MPLS’’ action that removes the last MPLS header from a packet provides this context,
as the Ethertype of the payload. See Layer 2.5: MPLS for more information.
OpenFlow and Open vSwitch support some fields other than data fields. Metadata fields relate to the
origin or treatment of a packet, but they are not extracted from the packet data itself. One example is
the physical port on which a packet arrived at the switch. Register fields act like variables: they give
an OpenFlow switch space for temporary storage while processing a packet. Existing metadata and register
fields have no prerequisites.
A field’s value consists of an integral number of bytes. For data fields, sometimes those bytes are taken
directly from the packet. Other data fields are copied from a packet with padding (usually with zeros and
in the most significant positions). The remaining data fields are transformed in other ways as they are
copied from the packets, to make them more useful for matching.
Matching
The most important use of fields in OpenFlow is matching, to determine whether particular field values
agree with a set of constraints called a match. A match consists of zero or more constraints on
individual fields, all of which must be met to satisfy the match. (A match that contains no constraints
is always satisfied.) OpenFlow and Open vSwitch support a number of forms of matching on individual
fields:
Exact match, e.g. nw_src=10.1.2.3
Only a particular value of the field is matched; for example, only one particular source IP
address. Exact matches are written as field=value. The forms accepted for value depend on
the field.
All fields support exact matches.
Bitwise match, e.g. nw_src=10.1.0.0/255.255.0.0
Specific bits in the field must have specified values; for example, only source IP
addresses in a particular subnet. Bitwise matches are written as field=value/mask, where
value and mask take one of the forms accepted for an exact match on field. Some fields
accept other forms for bitwise matches; for example, nw_src=10.1.0.0/255.255.0.0 may also
be written nw_src=10.1.0.0/16.
Most OpenFlow switches do not allow every bitwise matching on every field (and before
OpenFlow 1.2, the protocol did not even provide for the possibility for most fields). Even
switches that do allow bitwise matching on a given field may restrict the masks that are
allowed, e.g. by allowing matches only on contiguous sets of bits starting from the most
significant bit, that is, ``CIDR’’ masks [RFC 4632]. Open vSwitch does not allows bitwise
matching on every field, but it allows arbitrary bitwise masks on any field that does
support bitwise matching. (Older versions had some restrictions, as documented in the
descriptions of individual fields.)
Wildcard, e.g. ``any nw_src’’
The value of the field is not constrained. Wildcarded fields may be written as field=*,
although it is unusual to mention them at all. (When specifying a wildcard explicitly in a
command invocation, be sure to using quoting to protect against shell expansion.)
There is a tiny difference between wildcarding a field and not specifying any match on a
field: wildcarding a field requires satisfying the field’s prerequisites.
Some types of matches on individual fields cannot be expressed directly with OpenFlow and Open vSwitch.
These can be expressed indirectly:
Set match, e.g. ``tcp_dst ∈ {80, 443, 8080}’’
The value of a field is one of a specified set of values; for example, the TCP destination
port is 80, 443, or 8080.
For matches used in flows (see Flows, below), multiple flows can simulate set matches.
Range match, e.g. ``1000 ≤ tcp_dst ≤ 1999’’
The value of the field must lie within a numerical range, for example, TCP destination
ports between 1000 and 1999.
Range matches can be expressed as a collection of bitwise matches. For example, suppose
that the goal is to match TCP source ports 1000 to 1999, inclusive. The binary
representations of 1000 and 1999 are:
01111101000
11111001111
The following series of bitwise matches will match 1000 and 1999 and all the values in
between:
01111101xxx
0111111xxxx
10xxxxxxxxx
110xxxxxxxx
1110xxxxxxx
11110xxxxxx
1111100xxxx
which can be written as the following matches:
tcp,tp_src=0x03e8/0xfff8
tcp,tp_src=0x03f0/0xfff0
tcp,tp_src=0x0400/0xfe00
tcp,tp_src=0x0600/0xff00
tcp,tp_src=0x0700/0xff80
tcp,tp_src=0x0780/0xffc0
tcp,tp_src=0x07c0/0xfff0
Inequality match, e.g. ``tcp_dst ≠ 80’’
The value of the field differs from a specified value, for example, all TCP destination
ports except 80.
An inequality match on an n-bit field can be expressed as a disjunction of n 1-bit matches.
For example, the inequality match ``vlan_pcp ≠ 5’’ can be expressed as ``vlan_pcp = 0/4 or
vlan_pcp = 2/2 or vlan_pcp = 0/1.’’ For matches used in flows (see Flows, below), sometimes
one can more compactly express inequality as a higher-priority flow that matches the
exceptional case paired with a lower-priority flow that matches the general case.
Alternatively, an inequality match may be converted to a pair of range matches, e.g.
tcp_src ≠ 80 may be expressed as ``0 ≤ tcp_src < 80 or 80 < tcp_src ≤ 65535’’, and then
each range match may in turn be converted to a bitwise match.
Conjunctive match, e.g. ``tcp_src ∈ {80, 443, 8080} and tcp_dst ∈ {80, 443, 8080}’’
As an OpenFlow extension, Open vSwitch supports matching on conditions on conjunctions of
the previously mentioned forms of matching. See the documentation for conj_id for more
information.
All of these supported forms of matching are special cases of bitwise matching. In some cases this
influences the design of field values. ip_frag is the most prominent example: it is designed to make all
of the practically useful checks for IP fragmentation possible as a single bitwise match.
Shorthands
Some matches are very commonly used, so Open vSwitch accepts shorthand notations. In some cases, Open
vSwitch also uses shorthand notations when it displays matches. The following shorthands are defined,
with their long forms shown on the right side:
eth packet_type=(0,0) (Open vSwitch 2.8 and later)
ip eth_type=0x0800
ipv6 eth_type=0x86dd
icmp eth_type=0x0800,ip_proto=1
icmp6 eth_type=0x86dd,ip_proto=58
tcp eth_type=0x0800,ip_proto=6
tcp6 eth_type=0x86dd,ip_proto=6
udp eth_type=0x0800,ip_proto=17
udp6 eth_type=0x86dd,ip_proto=17
sctp eth_type=0x0800,ip_proto=132
sctp6 eth_type=0x86dd,ip_proto=132
arp eth_type=0x0806
rarp eth_type=0x8035
mpls eth_type=0x8847
mplsm eth_type=0x8848
Evolution of OpenFlow Fields
The discussion so far applies to all OpenFlow and Open vSwitch versions. This section starts to draw in
specific information by explaining, in broad terms, the treatment of fields and matches in each OpenFlow
version.
OpenFlow 1.0
OpenFlow 1.0 defined the OpenFlow protocol format of a match as a fixed-length data structure that could
match on the following fields:
• Ingress port.
• Ethernet source and destination MAC.
• Ethertype (with a special value to match frames that lack an Ethertype).
• VLAN ID and priority.
• IPv4 source, destination, protocol, and DSCP.
• TCP source and destination port.
• UDP source and destination port.
• ICMPv4 type and code.
• ARP IPv4 addresses (SPA and TPA) and opcode.
Each supported field corresponded to some member of the data structure. Some members represented multiple
fields, in the case of the TCP, UDP, ICMPv4, and ARP fields whose presence is mutually exclusive. This
also meant that some members were poor fits for their fields: only the low 8 bits of the 16-bit ARP
opcode could be represented, and the ICMPv4 type and code were padded with 8 bits of zeros to fit in the
16-bit members primarily meant for TCP and UDP ports. An additional bitmap member indicated, for each
member, whether its field should be an ``exact’’ or ``wildcarded’’ match (see Matching), with additional
support for CIDR prefix matching on the IPv4 source and destination fields.
Simplicity was recognized early on as the main virtue of this approach. Obviously, any fixed-length data
structure cannot support matching new protocols that do not fit. There was no room, for example, for
matching IPv6 fields, which was not a priority at the time. Lack of room to support matching the Ethernet
addresses inside ARP packets actually caused more of a design problem later, leading to an Open vSwitch
extension action specialized for dropping ``spoofed’’ ARP packets in which the frame and ARP Ethernet
source addressed differed. (This extension was never standardized. Open vSwitch dropped support for it a
few releases after it added support for full ARP matching.)
The design of the OpenFlow fixed-length matches also illustrates compromises, in both directions, between
the strengths and weaknesses of software and hardware that have always influenced the design of OpenFlow.
Support for matching ARP fields that do fit in the data structure was only added late in the design
process (and remained optional in OpenFlow 1.0), for example, because common switch ASICs did not support
matching these fields.
The compromises in favor of software occurred for more complicated reasons. The OpenFlow designers did
not know how to implement matching in software that was fast, dynamic, and general. (A way was later
found [Srinivasan].) Thus, the designers sought to support dynamic, general matching that would be fast
in realistic special cases, in particular when all of the matches were microflows, that is, matches that
specify every field present in a packet, because such matches can be implemented as a single hash table
lookup. Contemporary research supported the feasibility of this approach: the number of microflows in a
campus network had been measured to peak at about 10,000 [Casado, section 3.2]. (Calculations show that
this can only be true in a lightly loaded network [Pepelnjak].)
As a result, OpenFlow 1.0 required switches to treat microflow matches as the highest possible priority.
This let software switches perform the microflow hash table lookup first. Only on failure to match a
microflow did the switch need to fall back to checking the more general and presumed slower matches.
Also, the OpenFlow 1.0 flow match was minimally flexible, with no support for general bitwise matching,
partly on the basis that this seemed more likely amenable to relatively efficient software
implementation. (CIDR masking for IPv4 addresses was added relatively late in the OpenFlow 1.0 design
process.)
Microflow matching was later discovered to aid some hardware implementations. The TCAM chips used for
matching in hardware do not support priority in the same way as OpenFlow but instead tie priority to
ordering [Pagiamtzis]. Thus, adding a new match with a priority between the priorities of existing
matches can require reordering an arbitrary number of TCAM entries. On the other hand, when microflows
are highest priority, they can be managed as a set-aside portion of the TCAM entries.
The emphasis on matching microflows also led designers to carefully consider the bandwidth requirements
between switch and controller: to maximize the number of microflow setups per second, one must minimize
the size of each flow’s description. This favored the fixed-length format in use, because it expressed
common TCP and UDP microflows in fewer bytes than more flexible ``type-length-value’’ (TLV) formats.
(Early versions of OpenFlow also avoided TLVs in general to head off protocol fragmentation.)
Inapplicable Fields
OpenFlow 1.0 does not clearly specify how to treat inapplicable fields. The members for inapplicable
fields are always present in the match data structure, as are the bits that indicate whether the fields
are matched, and the ``correct’’ member and bit values for inapplicable fields is unclear. OpenFlow 1.0
implementations changed their behavior over time as priorities shifted. The early OpenFlow reference
implementation, motivated to make every flow a microflow to enable hashing, treated inapplicable fields
as exact matches on a value of 0. Initially, this behavior was implemented in the reference controller
only.
Later, the reference switch was also changed to actually force any wildcarded inapplicable fields into
exact matches on 0. The latter behavior sometimes caused problems, because the modified flow was the one
reported back to the controller later when it queried the flow table, and the modifications sometimes
meant that the controller could not properly recognize the flow that it had added. In retrospect, perhaps
this problem should have alerted the designers to a design error, but the ability to use a single hash
table was held to be more important than almost every other consideration at the time.
When more flexible match formats were introduced much later, they disallowed any mention of inapplicable
fields as part of a match. This raised the question of how to translate between this new format and the
OpenFlow 1.0 fixed format. It seemed somewhat inconsistent and backward to treat fields as exact-match in
one format and forbid matching them in the other, so instead the treatment of inapplicable fields in the
fixed-length format was changed from exact match on 0 to wildcarding. (A better classifier had by now
eliminated software performance problems with wildcards.)
The OpenFlow 1.0.1 errata (released only in 2012) added some additional explanation [OpenFlow 1.0.1,
section 3.4], but it did not mandate specific behavior because of variation among implementations.
OpenFlow 1.1
The OpenFlow 1.1 protocol match format was designed as a type/length/value (TLV) format to allow for
future flexibility. The specification standardized only a single type OFPMT_STANDARD (0) with a fixed-
size payload, described here. The additional fields and bitwise masks in OpenFlow 1.1 cause this match
structure to be over twice as large as in OpenFlow 1.0, 88 bytes versus 40.
OpenFlow 1.1 added support for the following fields:
• SCTP source and destination port.
• MPLS label and traffic control (TC) fields.
• One 64-bit register (named ``metadata’’).
OpenFlow 1.1 increased the width of the ingress port number field (and all other port numbers in the
protocol) from 16 bits to 32 bits.
OpenFlow 1.1 increased matching flexibility by introducing arbitrary bitwise matching on Ethernet and
IPv4 address fields and on the new ``metadata’’ register field. Switches were not required to support all
possible masks [OpenFlow 1.1, section 4.3].
By a strict reading of the specification, OpenFlow 1.1 removed support for matching ICMPv4 type and code
[OpenFlow 1.1, section A.2.3], but this is likely an editing error because ICMP matching is described
elsewhere [OpenFlow 1.1, Table 3, Table 4, Figure 4]. Open vSwitch does support ICMPv4 type and code
matching with OpenFlow 1.1.
OpenFlow 1.1 avoided the pitfalls of inapplicable fields that OpenFlow 1.0 encountered, by requiring the
switch to ignore the specified field values [OpenFlow 1.1, section A.2.3]. It also implied that the
switch should ignore the bits that indicate whether to match inapplicable fields.
Physical Ingress Port
OpenFlow 1.1 introduced a new pseudo-field, the physical ingress port. The physical ingress port is only
a pseudo-field because it cannot be used for matching. It appears only one place in the protocol, in the
``packet-in’’ message that passes a packet received at the switch to an OpenFlow controller.
A packet’s ingress port and physical ingress port are identical except for packets processed by a switch
feature such as bonding or tunneling that makes a packet appear to arrive on a ``virtual’’ port
associated with the bond or the tunnel. For such packets, the ingress port is the virtual port and the
physical ingress port is, naturally, the physical port. Open vSwitch implements both bonding and
tunneling, but its bonding implementation does not use virtual ports and its tunnels are typically not on
the same OpenFlow switch as their physical ingress ports (which need not be part of any switch), so the
ingress port and physical ingress port are always the same in Open vSwitch.
OpenFlow 1.2
OpenFlow 1.2 abandoned the fixed-length approach to matching. One reason was size, since adding support
for IPv6 address matching (now seen as important), with bitwise masks, would have added 64 bytes to the
match length, increasing it from 88 bytes in OpenFlow 1.1 to over 150 bytes. Extensibility had also
become important as controller writers increasingly wanted support for new fields without having to
change messages throughout the OpenFlow protocol. The challenges of carefully defining fixed-length
matches to avoid problems with inapplicable fields had also become clear over time.
Therefore, OpenFlow 1.2 adopted a flow format using a flexible type-length-value (TLV) representation, in
which each TLV expresses a match on one field. These TLVs were in turn encapsulated inside the outer TLV
wrapper introduced in OpenFlow 1.1 with the new identifier OFPMT_OXM (1). (This wrapper fulfilled its
intended purpose of reducing the amount of churn in the protocol when changing match formats; some
messages that included matches remained unchanged from OpenFlow 1.1 to 1.2 and later versions.)
OpenFlow 1.2 added support for the following fields:
• ARP hardware addresses (SHA and THA).
• IPv4 ECN.
• IPv6 source and destination addresses, flow label, DSCP, ECN, and protocol.
• TCP, UDP, and SCTP port numbers when encapsulated inside IPv6.
• ICMPv6 type and code.
• ICMPv6 Neighbor Discovery target address and source and target Ethernet addresses.
The OpenFlow 1.2 format, called OXM (OpenFlow Extensible Match), was modeled closely on an extension to
OpenFlow 1.0 introduced in Open vSwitch 1.1 called NXM (Nicira Extended Match). Each OXM or NXM TLV has
the following format:
type
<---------------->
16 7 1 8 length bytes
+------------+-----+--+------+ +------------+
|vendor/class|field|HM|length| | body |
+------------+-----+--+------+ +------------+
The most significant 16 bits of the NXM or OXM header, called vendor by NXM and class by OXM, identify an
organization permitted to allocate identifiers for fields. NXM allocates only two vendors, 0x0000 for
fields supported by OpenFlow 1.0 and 0x0001 for fields implemented as an Open vSwitch extension. OXM
assigns classes as follows:
0x0000 (OFPXMC_NXM_0).
0x0001 (OFPXMC_NXM_1).
Reserved for NXM compatibility.
0x0002 to 0x7fff
Reserved for allocation to ONF members, but none yet assigned.
0x8000 (OFPXMC_OPENFLOW_BASIC)
Used for most standard OpenFlow fields.
0x8001 (OFPXMC_PACKET_REGS)
Used for packet register fields in OpenFlow 1.5 and later.
0x8002 to 0xfffe
Reserved for the OpenFlow specification.
0xffff (OFPXMC_EXPERIMENTER)
Experimental use.
When class is 0xffff, the OXM header is extended to 64 bits by using the first 32 bits of the body as an
experimenter field whose most significant byte is zero and whose remaining bytes are an Organizationally
Unique Identifier (OUI) assigned by the IEEE [IEEE OUI], as shown below.
type experimenter
<----------> <---------->
16 7 1 8 8 24 (length - 4) bytes
+------+-----+--+------+ +------+-----+ +------------------+
|class |field|HM|length| | zero | OUI | | body |
+------+-----+--+------+ +------+-----+ +------------------+
0xffff 0x00
OpenFlow says that support for experimenter fields is optional. Open vSwitch 2.4 and later does support
them, so that it can support the following experimenter classes:
0x4f4e4600 (ONFOXM_ET)
Used by official Open Networking Foundation extensions in OpenFlow 1.3 and later. e.g. [TCP
Flags Match Field Extension].
0x005ad650 (NXOXM_NSH)
Used by Open vSwitch for NSH extensions, in the absence of an official ONF-assigned class.
(This OUI is randomly generated.)
Taken as a unit, class (or vendor), field, and experimenter (when present) uniquely identify a particular
field.
When hasmask (abbreviated HM above) is 0, the OXM is an exact match on an entire field. In this case, the
body (excluding the experimenter field, if present) is a single value to be matched.
When hasmask is 1, the OXM is a bitwise match. The body (excluding the experimenter field) consists of a
value to match, followed by the bitwise mask to apply. A 1-bit in the mask indicates that the
corresponding bit in the value should be matched and a 0-bit that it should be ignored. For example, for
an IP address field, a value of 192.168.0.0 followed by a mask of 255.255.0.0 would match addresses in
the 196.168.0.0/16 subnet.
• Some fields might not support masking at all, and some fields that do support masking might
restrict it to certain patterns. For example, fields that have IP address values might be
restricted to CIDR masks. The descriptions of individual fields note these restrictions.
• An OXM TLV with a mask that is all zeros is not useful (although it is not forbidden),
because it is has the same effect as omitting the TLV entirely.
• It is not meaningful to pair a 0-bit in an OXM mask with a 1-bit in its value, and Open
vSwitch rejects such an OXM with the error OFPBMC_BAD_WILDCARDS, as required by OpenFlow
1.3 and later.
The length identifies the number of bytes in the body, including the 4-byte experimenter header, if it is
present. Each OXM TLV has a fixed length; that is, given class, field, experimenter (if present), and
hasmask, length is a constant. The length is included explicitly to allow software to minimally parse OXM
TLVs of unknown types.
OXM TLVs must be ordered so that a field’s prerequisites are satisfied before it is parsed. For example,
an OXM TLV that matches on the IPv4 source address field is only allowed following an OXM TLV that
matches on the Ethertype for IPv4. Similarly, an OXM TLV that matches on the TCP source port must follow
a TLV that matches an Ethertype of IPv4 or IPv6 and one that matches an IP protocol of TCP (in that
order). The order of OXM TLVs is not otherwise restricted; no canonical ordering is defined.
A given field may be matched only once in a series of OXM TLVs.
OpenFlow 1.3
OpenFlow 1.3 showed OXM to be largely successful, by adding new fields without making any changes to how
flow matches otherwise worked. It added OXMs for the following fields supported by Open vSwitch:
• Tunnel ID for ports associated with e.g. VXLAN or keyed GRE.
• MPLS ``bottom of stack’’ (BOS) bit.
OpenFlow 1.3 also added OXMs for the following fields not documented here and not yet implemented by Open
vSwitch:
• IPv6 extension header handling.
• PBB I-SID.
OpenFlow 1.4
OpenFlow 1.4 added OXMs for the following fields not documented here and not yet implemented by Open
vSwitch:
• PBB UCA.
OpenFlow 1.5
OpenFlow 1.5 added OXMs for the following fields supported by Open vSwitch:
• Packet type.
• TCP flags.
• Packet registers.
• The output port in the OpenFlow action set.
FIELDS REFERENCE
The following sections document the fields that Open vSwitch supports. Each section provides introductory
material on a group of related fields, followed by information on each individual field. In addition to
field-specific information, each field begins with a table with entries for the following important
properties:
Name The field’s name, used for parsing and formatting the field, e.g. in ovs-ofctl commands.
For historical reasons, some fields have an additional name that is accepted as an
alternative in parsing. This name, when there is one, is listed as well, e.g. ``tun (aka
tunnel_id).’’
Width The field’s width, always a multiple of 8 bits. Some fields don’t use all of the bits, so
this may be accompanied by an explanation. For example, OpenFlow embeds the 2-bit IP ECN
field as as the low bits in an 8-bit byte, and so its width is expressed as ``8 bits (only
the least-significant 2 bits may be nonzero).’’
Format How a value for the field is formatted or parsed by, e.g., ovs-ofctl. Some possibilities
are generic:
decimal
Formats as a decimal number. On input, accepts decimal numbers or hexadecimal
numbers prefixed by 0x.
hexadecimal
Formats as a hexadecimal number prefixed by 0x. On input, accepts decimal numbers or
hexadecimal numbers prefixed by 0x. (The default for parsing is not hexadecimal:
only a 0x prefix causes input to be treated as hexadecimal.)
Ethernet
Formats and accepts the common Ethernet address format xx:xx:xx:xx:xx:xx.
IPv4 Formats and accepts the dotted-quad format a.b.c.d. For bitwise matches, formats and
accepts address/length CIDR notation in addition to address/mask.
IPv6 Formats and accepts the common IPv6 address formats, plus CIDR notation for bitwise
matches.
OpenFlow 1.0 port
Accepts 16-bit port numbers in decimal, plus OpenFlow well-known port names (e.g.
IN_PORT) in uppercase or lowercase.
OpenFlow 1.1+ port
Same syntax as OpenFlow 1.0 ports but for 32-bit OpenFlow 1.1+ port number fields.
Other, field-specific formats are explained along with their fields.
Masking
For most fields, this says ``arbitrary bitwise masks,’’ meaning that a flow may match any
combination of bits in the field. Some fields instead say ``exact match only,’’ which means
that a flow that matches on this field must match on the whole field instead of just
certain bits. Either way, this reports masking support for the latest version of Open
vSwitch using OXM or NXM (that is, either OpenFlow 1.2+ or OpenFlow 1.0 plus Open vSwitch
NXM extensions). In particular, OpenFlow 1.0 (without NXM) and 1.1 don’t always support
masking even if Open vSwitch itself does; refer to the OpenFlow 1.0 and OpenFlow 1.1 rows
to learn about masking with these protocol versions.
Prerequisites
Requirements that must be met to match on this field. For example, ip_src has IPv4 as a
prerequisite, meaning that a match must include eth_type=0x0800 to match on the IPv4 source
address. The following prerequisites, with their requirements, are currently in use:
none (no requirements)
VLAN VID
vlan_tci=0x1000/0x1000 (i.e. a VLAN header is present)
ARP eth_type=0x0806 (ARP) or eth_type=0x8035 (RARP)
IPv4 eth_type=0x0800
IPv6 eth_type=0x86dd
IPv4/IPv6
IPv4 or IPv6
MPLS eth_type=0x8847 or eth_type=0x8848
TCP IPv4/IPv6 and ip_proto=6
UDP IPv4/IPv6 and ip_proto=17
SCTP IPv4/IPv6 and ip_proto=132
ICMPv4 IPv4 and ip_proto=1
ICMPv6 IPv6 and ip_proto=58
ND solicit
ICMPv6 and icmp_type=135 and icmp_code=0
ND advert
ICMPv6 and icmp_type=136 and icmp_code=0
ND ND solicit or ND advert
The TCP, UDP, and SCTP prerequisites also have the special requirement that nw_frag is not
being used to select ``later fragments.’’ This is because only the first fragment of a
fragmented IPv4 or IPv6 datagram contains the TCP or UDP header.
Access Most fields are ``read/write,’’ which means that common OpenFlow actions like set_field can
modify them. Fields that are ``read-only’’ cannot be modified in these general-purpose
ways, although there may be other ways that actions can modify them.
OpenFlow 1.0
OpenFlow 1.1
These rows report the level of support that OpenFlow 1.0 or OpenFlow 1.1, respectively, has
for a field. For OpenFlow 1.0, supported fields are reported as either ``yes (exact match
only)’’ for fields that do not support any bitwise masking or ``yes (CIDR match only)’’ for
fields that support CIDR masking. OpenFlow 1.1 supported fields report either ``yes (exact
match only)’’ or simply ``yes’’ for fields that do support arbitrary masks. These OpenFlow
versions supported a fixed collection of fields that cannot be extended, so many more fields
are reported as ``not supported.’’
OXM
NXM These rows report the OXM and NXM code points that correspond to a given field. Either or
both may be ``none.’’
A field that has only an OXM code point is usually one that was standardized before it was
added to Open vSwitch. A field that has only an NXM code point is usually one that is not yet
standardized. When a field has both OXM and NXM code points, it usually indicates that it was
introduced as an Open vSwitch extension under the NXM code point, then later standardized
under the OXM code point. A field can have more than one OXM code point if it was
standardized in OpenFlow 1.4 or later and additionally introduced as an official ONF
extension for OpenFlow 1.3. (A field that has neither OXM nor NXM code point is typically an
obsolete field that is supported in some other form using OXM or NXM.)
Each code point in these rows is described in the form ``NAME (number) since OpenFlow spec
and Open vSwitch version,’’ e.g. ``OXM_OF_ETH_TYPE (5) since OpenFlow 1.2 and Open vSwitch
1.7.’’ First, NAME, which specifies a name for the code point, starts with a prefix that
designates a class and, in some cases, a vendor, as listed in the following table:
Prefix Vendor Class
─────────────── ─────────── ───────
NXM_OF (none) 0x0000
NXM_NX (none) 0x0001
ERICOXM_OF (none) 0x1000
OXM_OF (none) 0x8000
OXM_OF_PKT_REG (none) 0x8001
NXOXM_ET 0x00002320 0xffff
NXOXM_NSH 0x005ad650 0xffff
ONFOXM_ET 0x4f4e4600 0xffff
For more information on OXM/NXM classes and vendors, refer back to OpenFlow 1.2 under
Evolution of OpenFlow Fields. The number is the field number within the class and vendor. The
OpenFlow spec is the version of OpenFlow that standardized the code point. It is omitted for
NXM code points because they are nonstandard. The version is the version of Open vSwitch that
first supported the code point.
CONJUNCTIVE MATCH FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────── ────── ───── ──── ──────── ────────────────
conj_id 4 no no none OVS 2.4+
An individual OpenFlow flow can match only a single value for each field. However, situations often arise
where one wants to match one of a set of values within a field or fields. For matching a single field
against a set, it is straightforward and efficient to add multiple flows to the flow table, one for each
value in the set. For example, one might use the following flows to send packets with IP source address
a, b, c, or d to the OpenFlow controller:
ip,ip_src=a actions=controller
ip,ip_src=b actions=controller
ip,ip_src=c actions=controller
ip,ip_src=d actions=controller
Similarly, these flows send packets with IP destination address e, f, g, or h to the OpenFlow controller:
ip,ip_dst=e actions=controller
ip,ip_dst=f actions=controller
ip,ip_dst=g actions=controller
ip,ip_dst=h actions=controller
Installing all of the above flows in a single flow table yields a disjunctive effect: a packet is sent to
the controller if ip_src ∈ {a,b,c,d} or ip_dst ∈ {e,f,g,h} (or both). (Pedantically, if both of the above
sets of flows are present in the flow table, they should have different priorities, because OpenFlow says
that the results are undefined when two flows with same priority can both match a single packet.)
Suppose, on the other hand, one wishes to match conjunctively, that is, to send a packet to the
controller only if both ip_src ∈ {a,b,c,d} and ip_dst ∈ {e,f,g,h}. This requires 4 × 4 = 16 flows, one
for each possible pairing of ip_src and ip_dst. That is acceptable for our small example, but it does not
gracefully extend to larger sets or greater numbers of dimensions.
The conjunction action is a solution for conjunctive matches that is built into Open vSwitch. A
conjunction action ties groups of individual OpenFlow flows into higher-level ``conjunctive flows’’. Each
group corresponds to one dimension, and each flow within the group matches one possible value for the
dimension. A packet that matches one flow from each group matches the conjunctive flow.
To implement a conjunctive flow with conjunction, assign the conjunctive flow a 32-bit id, which must be
unique within an OpenFlow table. Assign each of the n ≥ 2 dimensions a unique number from 1 to n; the
ordering is unimportant. Add one flow to the OpenFlow flow table for each possible value of each
dimension with conjunction(id, k/n) as the flow’s actions, where k is the number assigned to the flow’s
dimension. Together, these flows specify the conjunctive flow’s match condition. When the conjunctive
match condition is met, Open vSwitch looks up one more flow that specifies the conjunctive flow’s actions
and receives its statistics. This flow is found by setting conj_id to the specified id and then again
searching the flow table.
The following flows provide an example. Whenever the IP source is one of the values in the flows that
match on the IP source (dimension 1 of 2), and the IP destination is one of the values in the flows that
match on IP destination (dimension 2 of 2), Open vSwitch searches for a flow that matches conj_id against
the conjunction ID (1234), finding the first flow listed below.
conj_id=1234 actions=controller
ip,ip_src=10.0.0.1 actions=conjunction(1234, 1/2)
ip,ip_src=10.0.0.4 actions=conjunction(1234, 1/2)
ip,ip_src=10.0.0.6 actions=conjunction(1234, 1/2)
ip,ip_src=10.0.0.7 actions=conjunction(1234, 1/2)
ip,ip_dst=10.0.0.2 actions=conjunction(1234, 2/2)
ip,ip_dst=10.0.0.5 actions=conjunction(1234, 2/2)
ip,ip_dst=10.0.0.7 actions=conjunction(1234, 2/2)
ip,ip_dst=10.0.0.8 actions=conjunction(1234, 2/2)
Many subtleties exist:
• In the example above, every flow in a single dimension has the same form, that is,
dimension 1 matches on ip_src and dimension 2 on ip_dst, but this is not a requirement.
Different flows within a dimension may match on different bits within a field (e.g. IP
network prefixes of different lengths, or TCP/UDP port ranges as bitwise matches), or even
on entirely different fields (e.g. to match packets for TCP source port 80 or TCP
destination port 80).
• The flows within a dimension can vary their matches across more than one field, e.g. to
match only specific pairs of IP source and destination addresses or L4 port numbers.
• A flow may have multiple conjunction actions, with different id values. This is useful for
multiple conjunctive flows with overlapping sets. If one conjunctive flow matches packets
with both ip_src ∈ {a,b} and ip_dst ∈ {d,e} and a second conjunctive flow matches ip_src ∈
{b,c} and ip_dst ∈ {f,g}, for example, then the flow that matches ip_src=b would have two
conjunction actions, one for each conjunctive flow. The order of conjunction actions within
a list of actions is not significant.
• A flow with conjunction actions may also include note actions for annotations, but not any
other kind of actions. (They would not be useful because they would never be executed.)
• All of the flows that constitute a conjunctive flow with a given id must have the same
priority. (Flows with the same id but different priorities are currently treated as
different conjunctive flows, that is, currently id values need only be unique within an
OpenFlow table at a given priority. This behavior isn’t guaranteed to stay the same in
later releases, so please use id values unique within an OpenFlow table.)
• Conjunctive flows must not overlap with each other, at a given priority, that is, any given
packet must be able to match at most one conjunctive flow at a given priority. Overlapping
conjunctive flows yield unpredictable results. (The flows that constitute a conjunctive
flow may overlap with those that constitute the same or another conjunctive flow.)
• Following a conjunctive flow match, the search for the flow with conj_id=id is done in the
same general-purpose way as other flow table searches, so one can use flows with conj_id=id
to act differently depending on circumstances. (One exception is that the search for the
conj_id=id flow itself ignores conjunctive flows, to avoid recursion.) If the search with
conj_id=id fails, Open vSwitch acts as if the conjunctive flow had not matched at all, and
continues searching the flow table for other matching flows.
• OpenFlow prerequisite checking occurs for the flow with conj_id=id in the same way as any
other flow, e.g. in an OpenFlow 1.1+ context, putting a mod_nw_src action into the example
above would require adding an ip match, like this:
conj_id=1234,ip actions=mod_nw_src:1.2.3.4,controller
• OpenFlow prerequisite checking also occurs for the individual flows that comprise a
conjunctive match in the same way as any other flow.
• The flows that constitute a conjunctive flow do not have useful statistics. They are never
updated with byte or packet counts, and so on. (For such a flow, therefore, the idle and
hard timeouts work much the same way.)
• Sometimes there is a choice of which flows include a particular match. For example, suppose
that we added an extra constraint to our example, to match on ip_src ∈ {a,b,c,d} and ip_dst
∈ {e,f,g,h} and tcp_dst = i. One way to implement this is to add the new constraint to the
conj_id flow, like this:
conj_id=1234,tcp,tcp_dst=i actions=mod_nw_src:1.2.3.4,controller
but this is not recommended because of the cost of the extra flow table lookup. Instead,
add the constraint to the individual flows, either in one of the dimensions or (slightly
better) all of them.
• A conjunctive match must have n ≥ 2 dimensions (otherwise a conjunctive match is not
necessary). Open vSwitch enforces this.
• Each dimension within a conjunctive match should ordinarily have more than one flow. Open
vSwitch does not enforce this.
Conjunction ID Field
Name: conj_id
Width: 32 bits
Format: decimal
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CONJ_ID (37) since Open vSwitch 2.4
Used for conjunctive matching. See above for more information.
TUNNEL FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────────────────── ──────────────── ───── ──── ──────── ─────────────────────
tun_id aka tunnel_id 8 yes yes none OF 1.3+ and OVS 1.1+
tun_src 4 yes yes none OVS 2.0+
tun_dst 4 yes yes none OVS 2.0+
tun_ipv6_src 16 yes yes none OVS 2.5+
tun_ipv6_dst 16 yes yes none OVS 2.5+
tun_gbp_id 2 yes yes none OVS 2.4+
tun_gbp_flags 1 yes yes none OVS 2.4+
tun_erspan_ver 1 (low 4 bits) yes yes none OVS 2.10+
tun_erspan_idx 4 (low 20 bits) yes yes none OVS 2.10+
tun_erspan_dir 1 (low 1 bits) yes yes none OVS 2.10+
tun_erspan_hwid 1 (low 6 bits) yes yes none OVS 2.10+
tun_gtpu_flags 1 yes no none OVS 2.13+
tun_gtpu_msgtype 1 yes no none OVS 2.13+
tun_metadata0 124 yes yes none OVS 2.5+
tun_metadata1 124 yes yes none OVS 2.5+
tun_metadata2 124 yes yes none OVS 2.5+
tun_metadata3 124 yes yes none OVS 2.5+
tun_metadata4 124 yes yes none OVS 2.5+
tun_metadata5 124 yes yes none OVS 2.5+
tun_metadata6 124 yes yes none OVS 2.5+
tun_metadata7 124 yes yes none OVS 2.5+
tun_metadata8 124 yes yes none OVS 2.5+
tun_metadata9 124 yes yes none OVS 2.5+
tun_metadata10 124 yes yes none OVS 2.5+
tun_metadata11 124 yes yes none OVS 2.5+
tun_metadata12 124 yes yes none OVS 2.5+
tun_metadata13 124 yes yes none OVS 2.5+
tun_metadata14 124 yes yes none OVS 2.5+
tun_metadata15 124 yes yes none OVS 2.5+
tun_metadata16 124 yes yes none OVS 2.5+
tun_metadata17 124 yes yes none OVS 2.5+
tun_metadata18 124 yes yes none OVS 2.5+
tun_metadata19 124 yes yes none OVS 2.5+
tun_metadata20 124 yes yes none OVS 2.5+
tun_metadata21 124 yes yes none OVS 2.5+
tun_metadata22 124 yes yes none OVS 2.5+
tun_metadata23 124 yes yes none OVS 2.5+
tun_metadata24 124 yes yes none OVS 2.5+
tun_metadata25 124 yes yes none OVS 2.5+
tun_metadata26 124 yes yes none OVS 2.5+
tun_metadata27 124 yes yes none OVS 2.5+
tun_metadata28 124 yes yes none OVS 2.5+
tun_metadata29 124 yes yes none OVS 2.5+
tun_metadata30 124 yes yes none OVS 2.5+
tun_metadata31 124 yes yes none OVS 2.5+
tun_metadata32 124 yes yes none OVS 2.5+
tun_metadata33 124 yes yes none OVS 2.5+
tun_metadata34 124 yes yes none OVS 2.5+
tun_metadata35 124 yes yes none OVS 2.5+
tun_metadata36 124 yes yes none OVS 2.5+
tun_metadata37 124 yes yes none OVS 2.5+
tun_metadata38 124 yes yes none OVS 2.5+
tun_metadata39 124 yes yes none OVS 2.5+
tun_metadata40 124 yes yes none OVS 2.5+
tun_metadata41 124 yes yes none OVS 2.5+
tun_metadata42 124 yes yes none OVS 2.5+
tun_metadata43 124 yes yes none OVS 2.5+
tun_metadata44 124 yes yes none OVS 2.5+
tun_metadata45 124 yes yes none OVS 2.5+
tun_metadata46 124 yes yes none OVS 2.5+
tun_metadata47 124 yes yes none OVS 2.5+
tun_metadata48 124 yes yes none OVS 2.5+
tun_metadata49 124 yes yes none OVS 2.5+
tun_metadata50 124 yes yes none OVS 2.5+
tun_metadata51 124 yes yes none OVS 2.5+
tun_metadata52 124 yes yes none OVS 2.5+
tun_metadata53 124 yes yes none OVS 2.5+
tun_metadata54 124 yes yes none OVS 2.5+
tun_metadata55 124 yes yes none OVS 2.5+
tun_metadata56 124 yes yes none OVS 2.5+
tun_metadata57 124 yes yes none OVS 2.5+
tun_metadata58 124 yes yes none OVS 2.5+
tun_metadata59 124 yes yes none OVS 2.5+
tun_metadata60 124 yes yes none OVS 2.5+
tun_metadata61 124 yes yes none OVS 2.5+
tun_metadata62 124 yes yes none OVS 2.5+
tun_metadata63 124 yes yes none OVS 2.5+
tun_flags 2 (low 1 bits) yes yes none OVS 2.5+
The fields in this group relate to tunnels, which Open vSwitch supports in several forms (GRE, VXLAN, and
so on). Most of these fields do appear in the wire format of a packet, so they are data fields from that
point of view, but they are metadata from an OpenFlow flow table point of view because they do not appear
in packets that are forwarded to the controller or to ordinary (non-tunnel) output ports.
Open vSwitch supports a spectrum of usage models for mapping tunnels to OpenFlow ports:
``Port-based’’ tunnels
In this model, an OpenFlow port represents one tunnel: it matches a particular type of
tunnel traffic between two IP endpoints, with a particular tunnel key (if keys are in use).
In this situation, in_port suffices to distinguish one tunnel from another, so the tunnel
header fields have little importance for OpenFlow processing. (They are still populated and
may be used if it is convenient.) The tunnel header fields play no role in sending packets
out such an OpenFlow port, either, because the OpenFlow port itself fully specifies the
tunnel headers.
The following Open vSwitch commands create a bridge br-int, add port tap0 to the bridge as
OpenFlow port 1, establish a port-based GRE tunnel between the local host and remote IP
192.168.1.1 using GRE key 5001 as OpenFlow port 2, and arranges to forward all traffic from
tap0 to the tunnel and vice versa:
ovs-vsctl add-br br-int
ovs-vsctl add-port br-int tap0 -- set interface tap0 ofport_request=1
ovs-vsctl add-port br-int gre0 -- \
set interface gre0 ofport_request=2 type=gre \
options:remote_ip=192.168.1.1 options:key=5001
ovs-ofctl add-flow br-int in_port=1,actions=2
ovs-ofctl add-flow br-int in_port=2,actions=1
``Flow-based’’ tunnels
In this model, one OpenFlow port represents all possible tunnels of a given type with an
endpoint on the current host, for example, all GRE tunnels. In this situation, in_port only
indicates that traffic was received on the particular kind of tunnel. This is where the
tunnel header fields are most important: they allow the OpenFlow tables to discriminate
among tunnels based on their IP endpoints or keys. Tunnel header fields also determine the
IP endpoints and keys of packets sent out such a tunnel port.
The following Open vSwitch commands create a bridge br-int, add port tap0 to the bridge as
OpenFlow port 1, establish a flow-based GRE tunnel port 3, and arranges to forward all
traffic from tap0 to remote IP 192.168.1.1 over a GRE tunnel with key 5001 and vice versa:
ovs-vsctl add-br br-int
ovs-vsctl add-port br-int tap0 -- set interface tap0 ofport_request=1
ovs-vsctl add-port br-int allgre -- \
set interface allgre ofport_request=3 type=gre \
options:remote_ip=flow options:key=flow
ovs-ofctl add-flow br-int \
’in_port=1 actions=set_tunnel:5001,set_field:192.168.1.1->tun_dst,3’
ovs-ofctl add-flow br-int ’in_port=3,tun_src=192.168.1.1,tun_id=5001 actions=1’
Mixed models.
One may define both flow-based and port-based tunnels at the same time. For example, it is
valid and possibly useful to create and configure both gre0 and allgre tunnel ports
described above.
Traffic is attributed on ingress to the most specific matching tunnel. For example, gre0 is
more specific than allgre. Therefore, if both exist, then gre0 will be the ingress port for
any GRE traffic received from 192.168.1.1 with key 5001.
On egress, traffic may be directed to any appropriate tunnel port. If both gre0 and allgre
are configured as already described, then the actions 2 and
set_tunnel:5001,set_field:192.168.1.1->tun_dst,3 send the same tunnel traffic.
Intermediate models.
Ports may be configured as partially flow-based. For example, one may define an OpenFlow
port that represents tunnels between a pair of endpoints but leaves the flow table to
discriminate on the flow key.
ovs-vswitchd.conf.db(5) describes all the details of tunnel configuration.
These fields do not have any prerequisites, which means that a flow may match on any or all of them, in
any combination.
These fields are zeros for packets that did not arrive on a tunnel.
Tunnel ID Field
Name: tun_id (aka tunnel_id)
Width: 64 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_TUNNEL_ID (38) since OpenFlow 1.3 and Open vSwitch 1.10
NXM: NXM_NX_TUN_ID (16) since Open vSwitch 1.1
Many kinds of tunnels support a tunnel ID:
• VXLAN and Geneve have a 24-bit virtual network identifier (VNI).
• LISP has a 24-bit instance ID.
• GRE has an optional 32-bit key.
• STT has a 64-bit key.
• ERSPAN has a 10-bit key (Session ID).
• GTPU has a 32-bit key (Tunnel Endpoint ID).
When a packet is received from a tunnel, this field holds the tunnel ID in its least significant bits,
zero-extended to fit. This field is zero if the tunnel does not support an ID, or if no ID is in use for
a tunnel type that has an optional ID, or if an ID of zero received, or if the packet was not received
over a tunnel.
When a packet is output to a tunnel port, the tunnel configuration determines whether the tunnel ID is
taken from this field or bound to a fixed value. See the earlier description of ``port-based’’ and
``flow-based’’ tunnels for more information.
The following diagram shows the origin of this field in a typical keyed GRE tunnel:
Ethernet IPv4 GRE Ethernet
<-----------> <---------------> <------------> <---------->
48 48 16 8 32 32 16 16 32 48 48 16
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
|dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
0x800 47 0x6558
Tunnel IPv4 Source Field
Name: tun_src
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV4_SRC (31) since Open vSwitch 2.0
When a packet is received from a tunnel, this field is the source address in the outer IP header of the
tunneled packet. This field is zero if the packet was not received over a tunnel.
When a packet is output to a flow-based tunnel port, this field influences the IPv4 source address used
to send the packet. If it is zero, then the kernel chooses an appropriate IP address based using the
routing table.
The following diagram shows the origin of this field in a typical keyed GRE tunnel:
Ethernet IPv4 GRE Ethernet
<-----------> <---------------> <------------> <---------->
48 48 16 8 32 32 16 16 32 48 48 16
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
|dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
0x800 47 0x6558
Tunnel IPv4 Destination Field
Name: tun_dst
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV4_DST (32) since Open vSwitch 2.0
When a packet is received from a tunnel, this field is the destination address in the outer IP header of
the tunneled packet. This field is zero if the packet was not received over a tunnel.
When a packet is output to a flow-based tunnel port, this field specifies the destination to which the
tunnel packet is sent.
The following diagram shows the origin of this field in a typical keyed GRE tunnel:
Ethernet IPv4 GRE Ethernet
<-----------> <---------------> <------------> <---------->
48 48 16 8 32 32 16 16 32 48 48 16
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
|dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
0x800 47 0x6558
Tunnel IPv6 Source Field
Name: tun_ipv6_src
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV6_SRC (109) since Open vSwitch 2.5
Similar to tun_src, but for tunnels over IPv6.
Tunnel IPv6 Destination Field
Name: tun_ipv6_dst
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV6_DST (110) since Open vSwitch 2.5
Similar to tun_dst, but for tunnels over IPv6.
VXLAN Group-Based Policy Fields
The VXLAN header is defined as follows [RFC 7348], where the I bit must be set to 1, unlabeled bits or
those labeled reserved must be set to 0, and Open vSwitch makes the VNI available via tun_id:
VXLAN flags
<------------->
1 1 1 1 1 1 1 1 24 24 8
+-+-+-+-+-+-+-+-+--------+---+--------+
| | | | |I| | | |reserved|VNI|reserved|
+-+-+-+-+-+-+-+-+--------+---+--------+
VXLAN Group-Based Policy [VXLAN Group Policy Option] adds new interpretations to existing bits in the
VXLAN header, reinterpreting it as follows, with changes highlighted:
GBP flags
<------------->
1 1 1 1 1 1 1 1 24 24 8
+-+-+-+-+-+-+-+-+---------------+---+--------+
| |D| | |A| | | |group policy ID|VNI|reserved|
+-+-+-+-+-+-+-+-+---------------+---+--------+
Open vSwitch makes GBP fields and flags available through the following fields. Only packets that arrive
over a VXLAN tunnel with the GBP extension enabled have these fields set. In other packets they are zero
on receive and ignored on transmit.
VXLAN Group-Based Policy ID Field
Name: tun_gbp_id
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_GBP_ID (38) since Open vSwitch 2.4
For a packet tunneled over VXLAN with the Group-Based Policy (GBP) extension, this field represents the
GBP policy ID, as shown above.
VXLAN Group-Based Policy Flags Field
Name: tun_gbp_flags
Width: 8 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_GBP_FLAGS (39) since Open vSwitch 2.4
For a packet tunneled over VXLAN with the Group-Based Policy (GBP) extension, this field represents the
GBP policy flags, as shown above.
The field has the format shown below:
GBP Flags
<------------->
1 1 1 1 1 1 1 1
+-+-+-+-+-+-+-+-+
| |D| | |A| | | |
+-+-+-+-+-+-+-+-+
Unlabeled bits are reserved and must be transmitted as 0. The VXLAN GBP draft defines the other bits’
meanings as:
D (Don’t Learn)
When set, this bit indicates that the egress tunnel endpoint must not learn the source
address of the encapsulated frame.
A (Applied)
When set, indicates that the group policy has already been applied to this packet. Devices
must not apply policies when the A bit is set.
ERSPAN Metadata Fields
These fields provide access to features in the ERSPAN tunneling protocol [ERSPAN], which has two major
versions: version 1 (aka type II) and version 2 (aka type III).
Regardless of version, ERSPAN is encapsulated within a fixed 8-byte GRE header that consists of a 4-byte
GRE base header and a 4-byte sequence number. The ERSPAN version 1 header format is:
GRE ERSPAN v1 Ethernet
<------------> <---------------------> <---------->
16 16 32 4 18 10 12 20 48 48 16
+---+------+---+ +---+---+-------+---+---+ +---+---+----+
|...| type |seq| |ver|...|session|...|idx| |dst|src|type| ...
+---+------+---+ +---+---+-------+---+---+ +---+---+----+
0x88be 1 tun_id
The ERSPAN version 2 header format is:
GRE ERSPAN v2 Ethernet
<------------> <----------------------------------------> <---------->
16 16 32 4 18 10 32 22 6 1 3 48 48 16
+---+------+---+ +---+---+-------+---------+---+----+---+---+ +---+---+----+
|...| type |seq| |ver|...|session|timestamp|...|hwid|dir|...| |dst|src|type| ...
+---+------+---+ +---+---+-------+---------+---+----+---+---+ +---+---+----+
0x22eb 2 tun_id 0/1
ERSPAN Version Field
Name: tun_erspan_ver
Width: 8 bits (only the least-significant 4 bits may be nonzero)
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_VER (12) since Open vSwitch 2.10
ERSPAN version number: 1 for version 1, or 2 for version 2.
ERSPAN Index Field
Name: tun_erspan_idx
Width: 32 bits (only the least-significant 20 bits may be nonzero)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_IDX (11) since Open vSwitch 2.10
This field is a 20-bit index/port number associated with the ERSPAN traffic’s source port and direction
(ingress/egress). This field is platform dependent.
ERSPAN Direction Field
Name: tun_erspan_dir
Width: 8 bits (only the least-significant 1 bits may be nonzero)
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_DIR (13) since Open vSwitch 2.10
For ERSPAN v2, the mirrored traffic’s direction: 0 for ingress traffic, 1 for egress traffic.
ERSPAN Hardware ID Field
Name: tun_erspan_hwid
Width: 8 bits (only the least-significant 6 bits may be nonzero)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_HWID (14) since Open vSwitch 2.10
A 6-bit unique identifier of an ERSPAN v2 engine within a system.
GTP-U Metadata Fields
These fields provide access to set-up GPRS Tunnelling Protocol for User Plane (GTPv1-U), based on 3GPP TS
29.281. A GTP-U header has the following format:
8 8 16 32
+-----+--------+------+----+
|flags|msg type|length|TEID| ...
+-----+--------+------+----+
The flags and message type have the Open vSwitch GTP-U specific fields described below. Open vSwitch
makes the TEID (Tunnel Endpoint Identifier), which identifies a tunnel endpoint in the receiving GTP-U
protocol entity, available via tun_id.
GTP-U Flags Field
Name: tun_gtpu_flags
Width: 8 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_GTPU_FLAGS (15) since Open vSwitch 2.13
This field holds the 8-bit GTP-U flags, encoded as:
GTP-U Tunnel Flags
<------------------->
3 1 1 1 1 1
+-------+--+---+-+-+--+
|version|PT|rsv|E|S|PN|
+-------+--+---+-+-+--+
1 0
The flags are:
version
Used to determine the version of the GTP-U protocol, which should be set to 1.
PT Protocol type, used as a protocol discriminator between GTP (1) and GTP’ (0).
rsv Reserved. Must be zero.
E If 1, indicates the presence of a meaningful value of the Next Extension Header field.
S If 1, indicates the presence of a meaningful value of the Sequence Number field.
PN If 1, indicates the presence of a meaningful value of the N-PDU Number field.
GTP-U Message Type Field
Name: tun_gtpu_msgtype
Width: 8 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_GTPU_MSGTYPE (16) since Open vSwitch 2.13
This field indicates whether it’s a signalling message used for path management, or a user plane message
which carries the original packet. The complete range of message types can be referred to [3GPP TS
29.281].
Geneve Fields
These fields provide access to additional features in the Geneve tunneling protocol [Geneve]. Their names
are somewhat generic in the hope that the same fields could be reused for other protocols in the future;
for example, the NSH protocol [NSH] supports TLV options whose form is identical to that for Geneve
options.
Generic Tunnel Option 0 Field
Name: tun_metadata0
Width: 992 bits (124 bytes)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_METADATA0 (40) since Open vSwitch 2.5
The above information specifically covers generic tunnel option 0, but Open vSwitch supports 64 options,
numbered 0 through 63, whose NXM field numbers are 40 through 103.
These fields provide OpenFlow access to the generic type-length-value options defined by the Geneve
tunneling protocol or other protocols with options in the same TLV format as Geneve options. Each of
these options has the following wire format:
header body
<-------------------> <------------------>
16 8 3 5 4×(length - 1) bytes
+-----+----+---+------+--------------------+
|class|type|res|length| value |
+-----+----+---+------+--------------------+
0
Taken together, the class and type in the option format mean that there are about 16 million distinct
kinds of TLV options, too many to give individual OXM code points. Thus, Open vSwitch requires the user
to define the TLV options of interest, by binding up to 64 TLV options to generic tunnel option NXM code
points. Each option may have up to 124 bytes in its body, the maximum allowed by the TLV format, but
bound options may total at most 252 bytes of body.
Open vSwitch extensions to the OpenFlow protocol bind TLV options to NXM code points. The ovs-ofctl(8)
program offers one way to use these extensions, e.g. to configure a mapping from a TLV option with class
0xffff, type 0, and a body length of 4 bytes:
ovs-ofctl add-tlv-map br0 "{class=0xffff,type=0,len=4}->tun_metadata0"
Once a TLV option is properly bound, it can be accessed and modified like any other field, e.g. to send
packets that have value 1234 for the option described above to the controller:
ovs-ofctl add-flow br0 tun_metadata0=1234,actions=controller
An option not received or not bound is matched as all zeros.
Tunnel Flags Field
Name: tun_flags
Width: 16 bits (only the least-significant 1 bits may be nonzero)
Format: tunnel flags
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_FLAGS (104) since Open vSwitch 2.5
Flags indicating various aspects of the tunnel encapsulation.
Matches on this field are most conveniently written in terms of symbolic names (given in the diagram
below), each preceded by either + for a flag that must be set, or - for a flag that must be unset,
without any other delimiters between the flags. Flags not mentioned are wildcarded. For example,
tun_flags=+oam matches only OAM packets. Matches can also be written as flags/mask, where flags and mask
are 16-bit numbers in decimal or in hexadecimal prefixed by 0x.
Currently, only one flag is defined:
oam The tunnel protocol indicated that this is an OAM (Operations and Management) control
packet.
The switch may reject matches against unknown flags.
Newer versions of Open vSwitch may introduce additional flags with new meanings. It is therefore not
recommended to use an exact match on this field since the behavior of these new flags is unknown and
should be ignored.
For non-tunneled packets, the value is 0.
METADATA FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
────────────── ────── ───── ──── ──────── ─────────────────────
in_port 2 no yes none OVS 1.1+
in_port_oxm 4 no yes none OF 1.2+ and OVS 1.7+
skb_priority 4 no no none
pkt_mark 4 yes yes none OVS 2.0+
actset_output 4 no no none OF 1.3+ and OVS 2.4+
packet_type 4 no no none OF 1.5+ and OVS 2.8+
These fields relate to the origin or treatment of a packet, but they are not extracted from the packet
data itself.
Ingress Port Field
Name: in_port
Width: 16 bits
Format: OpenFlow 1.0 port
Masking: not maskable
Prerequisites: none
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: none
NXM: NXM_OF_IN_PORT (0) since Open vSwitch 1.1
The OpenFlow port on which the packet being processed arrived. This is a 16-bit field that holds an
OpenFlow 1.0 port number. For receiving a packet, the only values that appear in this field are:
1 through 0xfeff (65,279), inclusive.
Conventional OpenFlow port numbers.
OFPP_LOCAL (0xfffe or 65,534).
The ``local’’ port, which in Open vSwitch is always named the same as the bridge itself.
This represents a connection between the switch and the local TCP/IP stack. This port is
where an IP address is most commonly configured on an Open vSwitch switch.
OpenFlow does not require a switch to have a local port, but all existing versions of Open
vSwitch have always included a local port. Future Directions: Future versions of Open
vSwitch might be able to optionally omit the local port, if someone submits code to
implement such a feature.
OFPP_NONE (OpenFlow 1.0) or OFPP_ANY (OpenFlow 1.1+) (0xffff or 65,535).
OFPP_CONTROLLER (0xfffd or 65,533).
When a controller injects a packet into an OpenFlow switch with a ``packet-out’’ request, it
can specify one of these ingress ports to indicate that the packet was generated internally
rather than having been received on some port.
OpenFlow 1.0 specified OFPP_NONE for this purpose. Despite that, some controllers used
OFPP_CONTROLLER, and some switches only accepted OFPP_CONTROLLER, so OpenFlow 1.0.2 required
support for both ports. OpenFlow 1.1 and later were more clearly drafted to allow only
OFPP_CONTROLLER. For maximum compatibility, Open vSwitch allows both ports with all OpenFlow
versions.
Values not mentioned above will never appear when receiving a packet, including the following notable
values:
0 Zero is not a valid OpenFlow port number.
OFPP_MAX (0xff00 or 65,280).
This value has only been clearly specified as a valid port number as of OpenFlow 1.3.3.
Before that, its status was unclear, and so Open vSwitch has never allowed OFPP_MAX to be
used as a port number, so packets will never be received on this port. (Other OpenFlow
switches, of course, might use it.)
OFPP_UNSET (0xfff7 or 65,527)
OFPP_IN_PORT (0xfff8 or 65,528)
OFPP_TABLE (0xfff9 or 65,529)
OFPP_NORMAL (0xfffa or 65,530)
OFPP_FLOOD (0xfffb or 65,531)
OFPP_ALL (0xfffc or 65,532)
These port numbers are used only in output actions and never appear as ingress ports.
Most of these port numbers were defined in OpenFlow 1.0, but OFPP_UNSET was only introduced
in OpenFlow 1.5.
Values that will never appear when receiving a packet may still be matched against in the flow table.
There are still circumstances in which those flows can be matched:
• The resubmit Open vSwitch extension action allows a flow table lookup with an arbitrary
ingress port.
• An action that modifies the ingress port field (see below), such as e.g. load or set_field,
followed by an action or instruction that performs another flow table lookup, such as
resubmit or goto_table.
This field is heavily used for matching in OpenFlow tables, but for packet egress, it has only very
limited roles:
• OpenFlow requires suppressing output actions to in_port. That is, the following two flows
both drop all packets that arrive on port 1:
in_port=1,actions=1
in_port=1,actions=drop
(This behavior is occasionally useful for flooding to a subset of ports. Specifying
actions=1,2,3,4, for example, outputs to ports 1, 2, 3, and 4, omitting the ingress port.)
• OpenFlow has a special port OFPP_IN_PORT (with value 0xfff8) that outputs to the ingress
port. For example, in a switch that has four ports numbered 1 through 4,
actions=1,2,3,4,in_port outputs to ports 1, 2, 3, and 4, including the ingress port.
Because the ingress port field has so little influence on packet processing, it does not ordinarily make
sense to modify the ingress port field. The field is writable only to support the occasional use case
where the ingress port’s roles in packet egress, described above, become troublesome. For example,
actions=load:0->NXM_OF_IN_PORT[],output:123 will output to port 123 regardless of whether it is in the
ingress port. If the ingress port is important, then one may save and restore it on the stack:
actions=push:NXM_OF_IN_PORT[],load:0->NXM_OF_IN_PORT[],output:123,pop:NXM_OF_IN_PORT[]
or, in Open vSwitch 2.7 or later, use the clone action to save and restore it:
actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
The ability to modify the ingress port is an Open vSwitch extension to OpenFlow.
OXM Ingress Port Field
Name: in_port_oxm
Width: 32 bits
Format: OpenFlow 1.1+ port
Masking: not maskable
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IN_PORT (0) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: none
OpenFlow 1.1 and later use a 32-bit port number, so this field supplies a 32-bit view of the ingress
port. Current versions of Open vSwitch support only a 16-bit range of ports:
• OpenFlow 1.0 ports 0x0000 to 0xfeff, inclusive, map to OpenFlow 1.1 port numbers with the
same values.
• OpenFlow 1.0 ports 0xff00 to 0xffff, inclusive, map to OpenFlow 1.1 port numbers 0xffffff00
to 0xffffffff.
• OpenFlow 1.1 ports 0x0000ff00 to 0xfffffeff are not mapped and not supported.
in_port and in_port_oxm are two views of the same information, so all of the comments on in_port apply to
in_port_oxm too. Modifying in_port changes in_port_oxm, and vice versa.
Setting in_port_oxm to an unsupported value yields unspecified behavior.
Output Queue Field
Name: skb_priority
Width: 32 bits
Format: hexadecimal
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: none
Future Directions: Open vSwitch implements the output queue as a field, but does not currently expose it
through OXM or NXM for matching purposes. If this turns out to be a useful feature, it could be
implemented in future versions. Only the set_queue, enqueue, and pop_queue actions currently influence
the output queue.
This field influences how packets in the flow will be queued, for quality of service (QoS) purposes, when
they egress the switch. Its range of meaningful values, and their meanings, varies greatly from one
OpenFlow implementation to another. Even within a single implementation, there is no guarantee that all
OpenFlow ports have the same queues configured or that all OpenFlow ports in an implementation can be
configured the same way queue-wise.
Configuring queues on OpenFlow is not well standardized. On Linux, Open vSwitch supports queue
configuration via OVSDB, specifically the QoS and Queue tables (see ovs-vswitchd.conf.db(5) for details).
Ports of Open vSwitch to other platforms might require queue configuration through some separate protocol
(such as a CLI). Even on Linux, Open vSwitch exposes only a fraction of the kernel’s queuing features
through OVSDB, so advanced or unusual uses might require use of separate utilities (e.g. tc). OpenFlow
switches other than Open vSwitch might use OF-CONFIG or any of the configuration methods mentioned above.
Finally, some OpenFlow switches have a fixed number of fixed-function queues (e.g. eight queues with
strictly defined priorities) and others do not support any control over queuing.
The only output queue that all OpenFlow implementations must support is zero, to identify a default
queue, whose properties are implementation-defined. Outputting a packet to a queue that does not exist on
the output port yields unpredictable behavior: among the possibilities are that the packet might be
dropped or transmitted with a very high or very low priority.
OpenFlow 1.0 only allowed output queues to be specified as part of an enqueue action that specified both
a queue and an output port. That is, OpenFlow 1.0 treats the queue as an argument to an action, not as a
field.
To increase flexibility, OpenFlow 1.1 added an action to set the output queue. This model was carried
forward, without change, through OpenFlow 1.5.
Open vSwitch implements the native queuing model of each OpenFlow version it supports. Open vSwitch also
includes an extension for setting the output queue as an action in OpenFlow 1.0.
When a packet ingresses into an OpenFlow switch, the output queue is ordinarily set to 0, indicating the
default queue. However, Open vSwitch supports various ways to forward a packet from one OpenFlow switch
to another within a single host. In these cases, Open vSwitch maintains the output queue across the
forwarding step. For example:
• A hop across an Open vSwitch ``patch port’’ (which does not actually involve queuing)
preserves the output queue.
• When a flow sets the output queue then outputs to an OpenFlow tunnel port, the
encapsulation preserves the output queue. If the kernel TCP/IP stack routes the
encapsulated packet directly to a physical interface, then that output honors the output
queue. Alternatively, if the kernel routes the encapsulated packet to another Open vSwitch
bridge, then the output queue set previously becomes the initial output queue on ingress to
the second bridge and will thus be used for further output actions (unless overridden by a
new ``set queue’’ action).
(This description reflects the current behavior of Open vSwitch on Linux. This behavior
relies on details of the Linux TCP/IP stack. It could be difficult to make ports to other
operating systems behave the same way.)
Packet Mark Field
Name: pkt_mark
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_PKT_MARK (33) since Open vSwitch 2.0
Packet mark comes to Open vSwitch from the Linux kernel, in which the sk_buff data structure that
represents a packet contains a 32-bit member named skb_mark. The value of skb_mark propagates along with
the packet it accompanies wherever the packet goes in the kernel. It has no predefined semantics but
various kernel-user interfaces can set and match on it, which makes it suitable for ``marking’’ packets
at one point in their handling and then acting on the mark later. With iptables, for example, one can
mark some traffic specially at ingress and then handle that traffic differently at egress based on the
marked value.
Packet mark is an attempt at a generalization of the skb_mark concept beyond Linux, at least through more
generic naming. Like skb_priority, packet mark is preserved across forwarding steps within a machine.
Unlike skb_priority, packet mark has no direct effect on packet forwarding: the value set in packet mark
does not matter unless some later OpenFlow table or switch matches on packet mark, or unless the packet
passes through some other kernel subsystem that has been configured to interpret packet mark in specific
ways, e.g. through iptables configuration mentioned above.
Preserving packet mark across kernel forwarding steps relies heavily on kernel support, which ports to
non-Linux operating systems may not have. Regardless of operating system support, Open vSwitch supports
packet mark within a single bridge and across patch ports.
The value of packet mark when a packet ingresses into the first Open vSwich bridge is typically zero, but
it could be nonzero if its value was previously set by some kernel subsystem.
Action Set Output Port Field
Name: actset_output
Width: 32 bits
Format: OpenFlow 1.1+ port
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: ONFOXM_ET_ACTSET_OUTPUT (43) since OpenFlow 1.3 and Open vSwitch 2.4;
OXM_OF_ACTSET_OUTPUT (43) since OpenFlow 1.5 and Open vSwitch 2.4
NXM: none
Holds the output port currently in the OpenFlow action set (i.e. from an output action within a
write_actions instruction). Its value is an OpenFlow port number. If there is no output port in the
OpenFlow action set, or if the output port will be ignored (e.g. because there is an output group in the
OpenFlow action set), then the value will be OFPP_UNSET.
Open vSwitch allows any table to match this field. OpenFlow, however, only requires this field to be
matchable from within an OpenFlow egress table (a feature that Open vSwitch does not yet implement).
Packet Type Field
Name: packet_type
Width: 32 bits
Format: packet type
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_PACKET_TYPE (44) since OpenFlow 1.5 and Open vSwitch 2.8
NXM: none
The type of the packet in the format specified in OpenFlow 1.5:
Packet type
<--------->
16 16
+---+-------+
|ns |ns_type| ...
+---+-------+
The upper 16 bits, ns, are a namespace. The meaning of ns_type depends on the namespace. The packet type
field is specified and displayed in the format (ns,ns_type).
Open vSwitch currently supports the following classes of packet types for matching:
(0,0) Ethernet.
(1,ethertype)
The specified ethertype. Open vSwitch can forward packets with any ethertype, but it can
only match on and process data fields for the following supported packet types:
(1,0x800)
IPv4
(1,0x806)
ARP
(1,0x86dd)
IPv6
(1,0x8847)
MPLS
(1,0x8848)
MPLS multicast
(1,0x8035)
RARP
(1,0x894f)
NSH
Consider the distinction between a packet with packet_type=(0,0), dl_type=0x800 and one with
packet_type=(1,0x800). The former is an Ethernet frame that contains an IPv4 packet, like this:
Ethernet IPv4
<-----------> <--------------->
48 48 16 8 32 32
+---+---+-----+ +---+-----+---+---+
|dst|src|type | |...|proto|src|dst| ...
+---+---+-----+ +---+-----+---+---+
0x800
The latter is an IPv4 packet not encapsulated inside any outer frame, like this:
IPv4
<--------------->
8 32 32
+---+-----+---+---+
|...|proto|src|dst| ...
+---+-----+---+---+
Matching on packet_type is a pre-requisite for matching on any data field, but for backward
compatibility, when a match on a data field is present without a packet_type match, Open vSwitch acts as
though a match on (0,0) (Ethernet) had been supplied. Similarly, when Open vSwitch sends flow match
information to a controller, e.g. in a reply to a request to dump the flow table, Open vSwitch omits a
match on packet type (0,0) if it would be implied by a data field match.
CONNECTION TRACKING FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────────── ────── ───── ──── ──────── ────────────────
ct_state 4 yes no none OVS 2.5+
ct_zone 2 no no none OVS 2.5+
ct_mark 4 yes yes none OVS 2.5+
ct_label 16 yes yes none OVS 2.5+
ct_nw_src 4 yes no CT OVS 2.8+
ct_nw_dst 4 yes no CT OVS 2.8+
ct_ipv6_src 16 yes no CT OVS 2.8+
ct_ipv6_dst 16 yes no CT OVS 2.8+
ct_nw_proto 1 no no CT OVS 2.8+
ct_tp_src 2 yes no CT OVS 2.8+
ct_tp_dst 2 yes no CT OVS 2.8+
Open vSwitch supports ``connection tracking,’’ which allows bidirectional streams of packets to be
statefully grouped into connections. Open vSwitch connection tracking, for example, identifies the
patterns of TCP packets that indicates a successfully initiated connection, as well as those that
indicate that a connection has been torn down. Open vSwitch connection tracking can also identify related
connections, such as FTP data connections spawned from FTP control connections.
An individual packet passing through the pipeline may be in one of two states, ``untracked’’ or
``tracked,’’ which may be distinguished via the ``trk’’ flag in ct_state. A packet is untracked at the
beginning of the Open vSwitch pipeline and continues to be untracked until the pipeline invokes the ct
action. The connection tracking fields are all zeroes in an untracked packet. When a flow in the Open
vSwitch pipeline invokes the ct action, the action initializes the connection tracking fields and the
packet becomes tracked for the remainder of its processing.
The connection tracker stores connection state in an internal table, but it only adds a new entry to this
table when a ct action for a new connection invokes ct with the commit parameter. For a given connection,
when a pipeline has executed ct, but not yet with commit, the connection is said to be uncommitted. State
for an uncommitted connection is ephemeral and does not persist past the end of the pipeline, so some
features are only available to committed connections. A connection would typically be left uncommitted as
a way to drop its packets.
Connection tracking is an Open vSwitch extension to OpenFlow. Open vSwitch 2.5 added the initial support
for connection tracking. Subsequent versions of Open vSwitch added many refinements and extensions to the
initial support. Many of these capabilities depend on the Open vSwitch datapath rather than simply the
userspace version. The capabilities column in the Datapath table (see ovs-vswitchd.conf.db(5)) reports
the detailed capabilities of a particular Open vSwitch datapath.
Connection Tracking State Field
Name: ct_state
Width: 32 bits
Format: ct state
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_STATE (105) since Open vSwitch 2.5
This field holds several flags that can be used to determine the state of the connection to which the
packet belongs.
Matches on this field are most conveniently written in terms of symbolic names (listed below), each
preceded by either + for a flag that must be set, or - for a flag that must be unset, without any other
delimiters between the flags. Flags not mentioned are wildcarded. For example, tcp,ct_state=+trk-new
matches TCP packets that have been run through the connection tracker and do not establish a new
connection. Matches can also be written as flags/mask, where flags and mask are 32-bit numbers in decimal
or in hexadecimal prefixed by 0x.
The following flags are defined:
new (0x01)
A new connection. Set to 1 if this is an uncommitted connection.
est (0x02)
Part of an existing connection. Set to 1 if packets of a committed connection have been
seen by conntrack from both directions.
rel (0x04)
Related to an existing connection, e.g. an ICMP ``destination unreachable’’ message or an
FTP data connections. This flag will only be 1 if the connection to which this one is
related is committed.
Connections identified as rel are separate from the originating connection and must be
committed separately. All packets for a related connection will have the rel flag set, not
just the initial packet.
rpl (0x08)
This packet is in the reply direction, meaning that it is in the opposite direction from
the packet that initiated the connection. This flag will only be 1 if the connection is
committed.
inv (0x10)
The state is invalid, meaning that the connection tracker couldn’t identify the connection.
This flag is a catch-all for problems in the connection or the connection tracker, such as:
• L3/L4 protocol handler is not loaded/unavailable. With the Linux kernel datapath,
this may mean that the nf_conntrack_ipv4 or nf_conntrack_ipv6 modules are not
loaded.
• L3/L4 protocol handler determines that the packet is malformed.
• Packets are unexpected length for protocol.
trk (0x20)
This packet is tracked, meaning that it has previously traversed the connection tracker. If
this flag is not set, then no other flags will be set. If this flag is set, then the packet
is tracked and other flags may also be set.
snat (0x40)
This packet was transformed by source address/port translation by a preceding ct action.
Open vSwitch 2.6 added this flag.
dnat (0x80)
This packet was transformed by destination address/port translation by a preceding ct
action. Open vSwitch 2.6 added this flag.
There are additional constraints on these flags, listed in decreasing order of precedence below:
1. If trk is unset, no other flags are set.
2. If trk is set, one or more other flags may be set.
3. If inv is set, only the trk flag is also set.
4. new and est are mutually exclusive.
5. new and rpl are mutually exclusive.
6. rel may be set in conjunction with any other flags.
Future versions of Open vSwitch may define new flags.
Connection Tracking Zone Field
Name: ct_zone
Width: 16 bits
Format: hexadecimal
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_ZONE (106) since Open vSwitch 2.5
A connection tracking zone, the zone value passed to the most recent ct action. Each zone is an
independent connection tracking context, so tracking the same packet in multiple contexts requires using
the ct action multiple times.
Connection Tracking Mark Field
Name: ct_mark
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_MARK (107) since Open vSwitch 2.5
The metadata committed, by an action within the exec parameter to the ct action, to the connection to
which the current packet belongs.
Connection Tracking Label Field
Name: ct_label
Width: 128 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_LABEL (108) since Open vSwitch 2.5
The label committed, by an action within the exec parameter to the ct action, to the connection to which
the current packet belongs.
Open vSwitch 2.8 introduced the matching support for connection tracker original direction 5-tuple
fields.
For non-committed non-related connections the conntrack original direction tuple fields always have the
same values as the corresponding headers in the packet itself. For any other packets of a committed
connection the conntrack original direction tuple fields reflect the values from that initial non-
committed non-related packet, and thus may be different from the actual packet headers, as the actual
packet headers may be in reverse direction (for reply packets), transformed by NAT (when nat option was
applied to the connection), or be of different protocol (i.e., when an ICMP response is sent to an UDP
packet). In case of related connections, e.g., an FTP data connection, the original direction tuple
contains the original direction headers from the parent connection, e.g., an FTP control connection.
The following fields are populated by the ct action, and require a match to a valid connection tracking
state as a prerequisite, in addition to the IP or IPv6 ethertype match. Examples of valid connection
tracking state matches include ct_state=+new, ct_state=+est, ct_state=+rel, and ct_state=+trk-inv.
Connection Tracking Original Direction IPv4 Source Address Field
Name: ct_nw_src
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_NW_SRC (120) since Open vSwitch 2.8
Matches IPv4 conntrack original direction tuple source address. See the paragraphs above for general
description to the conntrack original direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IPv4 Destination Address Field
Name: ct_nw_dst
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_NW_DST (121) since Open vSwitch 2.8
Matches IPv4 conntrack original direction tuple destination address. See the paragraphs above for general
description to the conntrack original direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IPv6 Source Address Field
Name: ct_ipv6_src
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_IPV6_SRC (122) since Open vSwitch 2.8
Matches IPv6 conntrack original direction tuple source address. See the paragraphs above for general
description to the conntrack original direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IPv6 Destination Address Field
Name: ct_ipv6_dst
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_IPV6_DST (123) since Open vSwitch 2.8
Matches IPv6 conntrack original direction tuple destination address. See the paragraphs above for general
description to the conntrack original direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IP Protocol Field
Name: ct_nw_proto
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_NW_PROTO (119) since Open vSwitch 2.8
Matches conntrack original direction tuple IP protocol type, which is specified as a decimal number
between 0 and 255, inclusive (e.g. 1 to match ICMP packets or 6 to match TCP packets). In case of, for
example, an ICMP response to an UDP packet, this may be different from the IP protocol type of the packet
itself. See the paragraphs above for general description to the conntrack original direction tuple.
Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction Transport Layer Source Port Field
Name: ct_tp_src
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_TP_SRC (124) since Open vSwitch 2.8
Bitwise match on the conntrack original direction tuple transport source, when MFF_CT_NW_PROTO has value
6 for TCP, 17 for UDP, or 132 for SCTP. When MFF_CT_NW_PROTO has value 1 for ICMP, or 58 for ICMPv6, the
lower 8 bits of MFF_CT_TP_SRC matches the conntrack original direction ICMP type. See the paragraphs
above for general description to the conntrack original direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction Transport Layer Source Port Field
Name: ct_tp_dst
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_TP_DST (125) since Open vSwitch 2.8
Bitwise match on the conntrack original direction tuple transport destination port, when MFF_CT_NW_PROTO
has value 6 for TCP, 17 for UDP, or 132 for SCTP. When MFF_CT_NW_PROTO has value 1 for ICMP, or 58 for
ICMPv6, the lower 8 bits of MFF_CT_TP_DST matches the conntrack original direction ICMP code. See the
paragraphs above for general description to the conntrack original direction tuple. Introduced in Open
vSwitch 2.8.
REGISTER FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────── ────── ───── ──── ──────── ─────────────────────
metadata 8 yes yes none OF 1.2+ and OVS 1.8+
reg0 4 yes yes none OVS 1.1+
reg1 4 yes yes none OVS 1.1+
reg2 4 yes yes none OVS 1.1+
reg3 4 yes yes none OVS 1.1+
reg4 4 yes yes none OVS 1.3+
reg5 4 yes yes none OVS 1.7+
reg6 4 yes yes none OVS 1.7+
reg7 4 yes yes none OVS 1.7+
reg8 4 yes yes none OVS 2.6+
reg9 4 yes yes none OVS 2.6+
reg10 4 yes yes none OVS 2.6+
reg11 4 yes yes none OVS 2.6+
reg12 4 yes yes none OVS 2.6+
reg13 4 yes yes none OVS 2.6+
reg14 4 yes yes none OVS 2.6+
reg15 4 yes yes none OVS 2.6+
xreg0 8 yes yes none OF 1.3+ and OVS 2.4+
xreg1 8 yes yes none OF 1.3+ and OVS 2.4+
xreg2 8 yes yes none OF 1.3+ and OVS 2.4+
xreg3 8 yes yes none OF 1.3+ and OVS 2.4+
xreg4 8 yes yes none OF 1.3+ and OVS 2.4+
xreg5 8 yes yes none OF 1.3+ and OVS 2.4+
xreg6 8 yes yes none OF 1.3+ and OVS 2.4+
xreg7 8 yes yes none OF 1.3+ and OVS 2.4+
xxreg0 16 yes yes none OVS 2.6+
xxreg1 16 yes yes none OVS 2.6+
xxreg2 16 yes yes none OVS 2.6+
xxreg3 16 yes yes none OVS 2.6+
These fields give an OpenFlow switch space for temporary storage while the pipeline is running. Whereas
metadata fields can have a meaningful initial value and can persist across some hops across OpenFlow
switches, registers are always initially 0 and their values never persist across inter-switch hops (not
even across patch ports).
OpenFlow Metadata Field
Name: metadata
Width: 64 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes
OXM: OXM_OF_METADATA (2) since OpenFlow 1.2 and Open vSwitch 1.8
NXM: none
This field is the oldest standardized OpenFlow register field, introduced in OpenFlow 1.1. It was
introduced to model the limited number of user-defined bits that some ASIC-based switches can carry
through their pipelines. Because of hardware limitations, OpenFlow allows switches to support writing and
masking only an implementation-defined subset of bits, even no bits at all. The Open vSwitch software
switch always supports all 64 bits, but of course an Open vSwitch port to an ASIC would have the same
restriction as the ASIC itself.
This field has an OXM code point, but OpenFlow 1.4 and earlier allow it to be modified only with a
specialized instruction, not with a ``set-field’’ action. OpenFlow 1.5 removes this restriction. Open
vSwitch does not enforce this restriction, regardless of OpenFlow version.
Register 0 Field
Name: reg0
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_REG0 (0) since Open vSwitch 1.1
This is the first of several Open vSwitch registers, all of which have the same properties. Open vSwitch
1.1 introduced registers 0, 1, 2, and 3, version 1.3 added register 4, version 1.7 added registers 5, 6,
and 7, and version 2.6 added registers 8 through 15.
Extended Register 0 Field
Name: xreg0
Width: 64 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_PKT_REG0 (0) since OpenFlow 1.3 and Open vSwitch 2.4
NXM: none
This is the first of the registers introduced in OpenFlow 1.5. OpenFlow 1.5 calls these fields just the
``packet registers,’’ but Open vSwitch already had 32-bit registers by that name, so Open vSwitch uses
the name ``extended registers’’ in an attempt to reduce confusion. The standard allows for up to 128
registers, each 64 bits wide, but Open vSwitch only implements 4 (in versions 2.4 and 2.5) or 8 (in
version 2.6 and later).
Each of the 64-bit extended registers overlays two of the 32-bit registers: xreg0 overlays reg0 and reg1,
with reg0 supplying the most-significant bits of xreg0 and reg1 the least-significant. Similarly, xreg1
overlays reg2 and reg3, and so on.
The OpenFlow specification says, ``In most cases, the packet registers can not be matched in tables, i.e.
they usually can not be used in the flow entry match structure’’ [OpenFlow 1.5, section 7.2.3.10], but
there is no reason for a software switch to impose such a restriction, and Open vSwitch does not.
Double-Extended Register 0 Field
Name: xxreg0
Width: 128 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_XXREG0 (111) since Open vSwitch 2.6
This is the first of the double-extended registers introduce in Open vSwitch 2.6. Each of the 128-bit
extended registers overlays four of the 32-bit registers: xxreg0 overlays reg0 through reg3, with reg0
supplying the most-significant bits of xxreg0 and reg3 the least-significant. xxreg1 similarly overlays
reg4 through reg7, and so on.
LAYER 2 (ETHERNET) FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────────────────── ────── ───── ──── ───────── ─────────────────────
eth_src aka dl_src 6 yes yes Ethernet OF 1.2+ and OVS 1.1+
eth_dst aka dl_dst 6 yes yes Ethernet OF 1.2+ and OVS 1.1+
eth_type aka dl_type 2 no no Ethernet OF 1.2+ and OVS 1.1+
Ethernet is the only layer-2 protocol that Open vSwitch supports. As with most software, Open vSwitch and
OpenFlow regard an Ethernet frame to begin with the 14-byte header and end with the final byte of the
payload; that is, the frame check sequence is not considered part of the frame.
Ethernet Source Field
Name: eth_src (aka dl_src)
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ETH_SRC (4) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ETH_SRC (2) since Open vSwitch 1.1
The Ethernet source address:
Ethernet
<---------->
48 48 16
+---+---+----+
|dst|src|type| ...
+---+---+----+
Ethernet Destination Field
Name: eth_dst (aka dl_dst)
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ETH_DST (3) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ETH_DST (1) since Open vSwitch 1.1
The Ethernet destination address:
Ethernet
<---------->
48 48 16
+---+---+----+
|dst|src|type| ...
+---+---+----+
Open vSwitch 1.8 and later support arbitrary masks for source and/or destination. Earlier versions only
support masking the destination with the following masks:
01:00:00:00:00:00
Match only the multicast bit. Thus, dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 matches all
multicast (including broadcast) Ethernet packets, and
dl_dst=00:00:00:00:00:00/01:00:00:00:00:00 matches all unicast Ethernet packets.
fe:ff:ff:ff:ff:ff
Match all bits except the multicast bit. This is probably not useful.
ff:ff:ff:ff:ff:ff
Exact match (equivalent to omitting the mask).
00:00:00:00:00:00
Wildcard all bits (equivalent to dl_dst=*).
Ethernet Type Field
Name: eth_type (aka dl_type)
Width: 16 bits
Format: hexadecimal
Masking: not maskable
Prerequisites: Ethernet
Access: read-only
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ETH_TYPE (5) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ETH_TYPE (3) since Open vSwitch 1.1
The most commonly seen Ethernet frames today use a format called ``Ethernet II,’’ in which the last two
bytes of the Ethernet header specify the Ethertype. For such a frame, this field is copied from those
bytes of the header, like so:
Ethernet
<---------------->
48 48 16
+---+---+----------+
|dst|src| type | ...
+---+---+----------+
≥0x600
Every Ethernet type has a value 0x600 (1,536) or greater. When the last two bytes of the Ethernet header
have a value too small to be an Ethernet type, then the value found there is the total length of the
frame in bytes, excluding the Ethernet header. An 802.2 LLC header typically follows the Ethernet header.
OpenFlow and Open vSwitch only support LLC headers with DSAP and SSAP 0xaa and control byte 0x03, which
indicate that a SNAP header follows the LLC header. In turn, OpenFlow and Open vSwitch only support a
SNAP header with organization 0x000000. In such a case, this field is copied from the type field in the
SNAP header, like this:
Ethernet LLC SNAP
<------------> <------------> <----------------->
48 48 16 8 8 8 24 16
+---+---+------+ +----+----+----+ +--------+----------+
|dst|src| type | |DSAP|SSAP|cntl| | org | type | ...
+---+---+------+ +----+----+----+ +--------+----------+
<0x600 0xaa 0xaa 0x03 0x000000 ≥0x600
When an 802.1Q header is inserted after the Ethernet source and destination, this field is populated with
the encapsulated Ethertype, not the 802.1Q Ethertype. With an Ethernet II inner frame, the result looks
like this:
Ethernet 802.1Q Ethertype
<------> <--------> <-------->
48 48 16 16 16
+----+---+ +------+---+ +----------+
|dst |src| | TPID |TCI| | type | ...
+----+---+ +------+---+ +----------+
0x8100 ≥0x600
LLC and SNAP encapsulation look like this with an 802.1Q header:
Ethernet 802.1Q Ethertype LLC SNAP
<------> <--------> <-------> <------------> <----------------->
48 48 16 16 16 8 8 8 24 16
+----+---+ +------+---+ +---------+ +----+----+----+ +--------+----------+
|dst |src| | TPID |TCI| | type | |DSAP|SSAP|cntl| | org | type | ...
+----+---+ +------+---+ +---------+ +----+----+----+ +--------+----------+
0x8100 <0x600 0xaa 0xaa 0x03 0x000000 ≥0x600
When a packet doesn’t match any of the header formats described above, Open vSwitch and OpenFlow set this
field to 0x5ff (OFP_DL_TYPE_NOT_ETH_TYPE).
VLAN FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────────── ──────────────── ───── ──── ───────── ─────────────────────
dl_vlan 2 (low 12 bits) no yes Ethernet
dl_vlan_pcp 1 (low 3 bits) no yes Ethernet
vlan_vid 2 (low 12 bits) yes yes Ethernet OF 1.2+ and OVS 1.7+
vlan_pcp 1 (low 3 bits) no yes VLAN VID OF 1.2+ and OVS 1.7+
vlan_tci 2 yes yes Ethernet OVS 1.1+
The 802.1Q VLAN header causes more trouble than any other 4 bytes in networking. OpenFlow 1.0, 1.1, and
1.2+ all treat VLANs differently. Open vSwitch extensions add another variant to the mix. Open vSwitch
reconciles all four treatments as best it can.
VLAN Header Format
An 802.1Q VLAN header consists of two 16-bit fields:
TPID TCI
<-------> <--------->
16 3 1 12
+---------+---+---+---+
|Ethertype|PCP|CFI|VID|
+---------+---+---+---+
0x8100 0
The first 16 bits of the VLAN header, the TPID (Tag Protocol IDentifier), is an Ethertype. When the VLAN
header is inserted just after the source and destination MAC addresses in a Ethertype frame, the TPID
serves to identify the presence of the VLAN. The standard TPID, the only one that Open vSwitch supports,
is 0x8100. OpenFlow 1.0 explicitly supports only TPID 0x8100. OpenFlow 1.1, but not earlier or later
versions, also requires support for TPID 0x88a8 (Open vSwitch does not support this). OpenFlow 1.2
through 1.5 do not require support for specific TPIDs (the ``push vlan header’’ action does say that only
0x8100 and 0x88a8 should be pushed). No version of OpenFlow provides a way to distinguish or match on the
TPID.
The remaining 16 bits of the VLAN header, the TCI (Tag Control Information), is subdivided into three
subfields:
• PCP (Priority Control Point), is a 3-bit 802.1p priority. The lowest priority is value 1,
the second-lowest is value 0, and priority increases from 2 up to highest priority 7.
• CFI (Canonical Format Indicator), is a 1-bit field. On an Ethernet network, its value is
always 0. This led to it later being repurposed under the name DEI (Drop Eligibility
Indicator). By either name, OpenFlow and Open vSwitch don’t provide any way to match or set
this bit.
• VID (VLAN IDentifier), is a 12-bit VLAN. If the VID is 0, then the frame is not part of a
VLAN. In that case, the VLAN header is called a priority tag because it is only meaningful
for assigning the frame a priority. VID 0xfff (4,095) is reserved.
See eth_type for illustrations of a complete Ethernet frame with 802.1Q tag included.
Multiple VLANs
Open vSwitch can match only a single VLAN header. If more than one VLAN header is present, then eth_type
holds the TPID of the inner VLAN header. Open vSwitch stops parsing the packet after the inner TPID, so
matching further into the packet (e.g. on the inner TCI or L3 fields) is not possible.
OpenFlow only directly supports matching a single VLAN header. In OpenFlow 1.1 or later, one OpenFlow
table can match on the outermost VLAN header and pop it off, and a later OpenFlow table can match on the
next outermost header. Open vSwitch does not support this.
VLAN Field Details
The four variants have three different levels of expressiveness: OpenFlow 1.0 and 1.1 VLAN matching are
less powerful than OpenFlow 1.2+ VLAN matching, which is less powerful than Open vSwitch extension VLAN
matching.
OpenFlow 1.0 VLAN Fields
OpenFlow 1.0 uses two fields, called dl_vlan and dl_vlan_pcp, each of which can be either exact-matched
or wildcarded, to specify VLAN matches:
• When both dl_vlan and dl_vlan_pcp are wildcarded, the flow matches packets without an
802.1Q header or with any 802.1Q header.
• The match dl_vlan=0xffff causes a flow to match only packets without an 802.1Q header. Such
a flow should also wildcard dl_vlan_pcp, since a packet without an 802.1Q header does not
have a PCP. OpenFlow does not specify what to do if a match on PCP is actually present, but
Open vSwitch ignores it.
• Otherwise, the flow matches only packets with an 802.1Q header. If dl_vlan is not
wildcarded, then the flow only matches packets with the VLAN ID specified in dl_vlan’s low
12 bits. If dl_vlan_pcp is not wildcarded, then the flow only matches packets with the
priority specified in dl_vlan_pcp’s low 3 bits.
OpenFlow does not specify how to interpret the high 4 bits of dl_vlan or the high 5 bits of
dl_vlan_pcp. Open vSwitch ignores them.
OpenFlow 1.1 VLAN Fields
VLAN matching in OpenFlow 1.1 is similar to OpenFlow 1.0. The one refinement is that when dl_vlan matches
on 0xfffe (OFVPID_ANY), the flow matches only packets with an 802.1Q header, with any VLAN ID. If
dl_vlan_pcp is wildcarded, the flow matches any packet with an 802.1Q header, regardless of VLAN ID or
priority. If dl_vlan_pcp is not wildcarded, then the flow only matches packets with the priority
specified in dl_vlan_pcp’s low 3 bits.
OpenFlow 1.1 uses the name OFPVID_NONE, instead of OFP_VLAN_NONE, for a dl_vlan of 0xffff, but it has the
same meaning.
In OpenFlow 1.1, Open vSwitch reports error OFPBMC_BAD_VALUE for an attempt to match on dl_vlan between
4,096 and 0xfffd, inclusive, or dl_vlan_pcp greater than 7.
OpenFlow 1.2 VLAN Fields
OpenFlow 1.2+ VLAN ID Field
Name: vlan_vid
Width: 16 bits (only the least-significant 12 bits may be nonzero)
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_VLAN_VID (6) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: none
The OpenFlow standard describes this field as consisting of ``12+1’’ bits. On ingress, its value is 0 if
no 802.1Q header is present, and otherwise it holds the VLAN VID in its least significant 12 bits, with
bit 12 (0x1000 aka OFPVID_PRESENT) also set to 1. The three most significant bits are always zero:
OXM_OF_VLAN_VID
<------------->
3 1 12
+---+--+--------+
| |P |VLAN ID |
+---+--+--------+
0
As a consequence of this field’s format, one may use it to match the VLAN ID in all of the ways available
with the OpenFlow 1.0 and 1.1 formats, and a few new ways:
Fully wildcarded
Matches any packet, that is, one without an 802.1Q header or with an 802.1Q header with any
TCI value.
Value 0x0000 (OFPVID_NONE), mask 0xffff (or no mask)
Matches only packets without an 802.1Q header.
Value 0x1000, mask 0x1000
Matches any packet with an 802.1Q header, regardless of VLAN ID.
Value 0x1009, mask 0xffff (or no mask)
Match only packets with an 802.1Q header with VLAN ID 9.
Value 0x1001, mask 0x1001
Matches only packets that have an 802.1Q header with an odd-numbered VLAN ID. (This is just
an example; one can match on any desired VLAN ID bit pattern.)
OpenFlow 1.2+ VLAN Priority Field
Name: vlan_pcp
Width: 8 bits (only the least-significant 3 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: VLAN VID
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_VLAN_PCP (7) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: none
The 3 least significant bits may be used to match the PCP bits in an 802.1Q header. Other bits are always
zero:
OXM_OF_VLAN_VID
<------------->
5 3
+--------+------+
| zero | PCP |
+--------+------+
0
This field may only be used when vlan_vid is not wildcarded and does not exact match on 0 (which only
matches when there is no 802.1Q header).
See VLAN Comparison Chart, below, for some examples.
Open vSwitch Extension VLAN Field
The vlan_tci extension can describe more kinds of VLAN matches than the other variants. It is also
simpler than the other variants.
VLAN TCI Field
Name: vlan_tci
Width: 16 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: none
NXM: NXM_OF_VLAN_TCI (4) since Open vSwitch 1.1
For a packet without an 802.1Q header, this field is zero. For a packet with an 802.1Q header, this field
is the TCI with the bit in CFI’s position (marked P for ``present’’ below) forced to 1. Thus, for a
packet in VLAN 9 with priority 7, it has the value 0xf009:
NXM_VLAN_TCI
<---------->
3 1 12
+----+--+----+
|PCP |P |VID |
+----+--+----+
7 1 9
Usage examples:
vlan_tci=0
Match packets without an 802.1Q header.
vlan_tci=0x1000/0x1000
Match packets with an 802.1Q header, regardless of VLAN and priority values.
vlan_tci=0xf123
Match packets tagged with priority 7 in VLAN 0x123.
vlan_tci=0x1123/0x1fff
Match packets tagged with VLAN 0x123 (and any priority).
vlan_tci=0x5000/0xf000
Match packets tagged with priority 2 (in any VLAN).
vlan_tci=0/0xfff
Match packets with no 802.1Q header or tagged with VLAN 0 (and any priority).
vlan_tci=0x5000/0xe000
Match packets with no 802.1Q header or tagged with priority 2 (in any VLAN).
vlan_tci=0/0xefff
Match packets with no 802.1Q header or tagged with VLAN 0 and priority 0.
See VLAN Comparison Chart, below, for more examples.
VLAN Comparison Chart
The following table describes each of several possible matching criteria on 802.1Q header may be
expressed with each variation of the VLAN matching fields:
Criteria OpenFlow 1.0 OpenFlow 1.1 OpenFlow 1.2+ NXM
───────── ───────────── ───────────── ────────────── ──────────
[1] ????/1,??/? ????/1,??/? 0000/0000,-- 0000/0000
[2] ffff/0,??/? ffff/0,??/? 0000/ffff,-- 0000/ffff
[3] 0xxx/0,??/1 0xxx/0,??/1 1xxx/ffff,-- 1xxx/1fff
[4] ????/1,0y/0 fffe/0,0y/0 1000/1000,0y z000/f000
[5] 0xxx/0,0y/0 0xxx/0,0y/0 1xxx/ffff,0y zxxx/ffff
[6] (none) (none) 1001/1001,-- 1001/1001
[7] (none) (none) (none) 3000/3000
[8] (none) (none) (none) 0000/0fff
[9] (none) (none) (none) 0000/f000
[10] (none) (none) (none) 0000/efff
All numbers in the table are expressed in hexadecimal. The columns in the table are interpreted as
follows:
Criteria
See the list below.
OpenFlow 1.0
OpenFlow 1.1
wwww/x,yy/z means VLAN ID match value wwww with wildcard bit x and VLAN PCP match value yy
with wildcard bit z. ? means that the given bits are ignored (and conventionally 0 for wwww
or yy, conventionally 1 for x or z). ``(none)’’ means that OpenFlow 1.0 (or 1.1) cannot match
with these criteria.
OpenFlow 1.2+
xxxx/yyyy,zz means vlan_vid with value xxxx and mask yyyy, and vlan_pcp (which is not
maskable) with value zz. -- means that vlan_pcp is omitted. ``(none)’’ means that OpenFlow
1.2 cannot match with these criteria.
NXM xxxx/yyyy means vlan_tci with value xxxx and mask yyyy.
The matching criteria described by the table are:
[1] Matches any packet, that is, one without an 802.1Q header or with an 802.1Q header with any
TCI value.
[2] Matches only packets without an 802.1Q header.
OpenFlow 1.0 doesn’t define the behavior if dl_vlan is set to 0xffff and dl_vlan_pcp is not
wildcarded. (Open vSwitch always ignores dl_vlan_pcp when dl_vlan is set to 0xffff.)
OpenFlow 1.1 says explicitly to ignore dl_vlan_pcp when dl_vlan is set to 0xffff.
OpenFlow 1.2 doesn’t say how to interpret a match with vlan_vid value 0 and a mask with
OFPVID_PRESENT (0x1000) set to 1 and some other bits in the mask set to 1 also. Open
vSwitch interprets it the same way as a mask of 0x1000.
Any NXM match with vlan_tci value 0 and the CFI bit set to 1 in the mask is equivalent to
the one listed in the table.
[3] Matches only packets that have an 802.1Q header with VID xxx (and any PCP).
[4] Matches only packets that have an 802.1Q header with PCP y (and any VID).
OpenFlow 1.0 doesn’t clearly define the behavior for this case. Open vSwitch implements it
this way.
In the NXM value, z equals (y << 1) | 1.
[5] Matches only packets that have an 802.1Q header with VID xxx and PCP y.
In the NXM value, z equals (y << 1) | 1.
[6] Matches only packets that have an 802.1Q header with an odd-numbered VID (and any PCP).
Only possible with OpenFlow 1.2 and NXM. (This is just an example; one can match on any
desired VID bit pattern.)
[7] Matches only packets that have an 802.1Q header with an odd-numbered PCP (and any VID).
Only possible with NXM. (This is just an example; one can match on any desired VID bit
pattern.)
[8] Matches packets with no 802.1Q header or with an 802.1Q header with a VID of 0. Only
possible with NXM.
[9] Matches packets with no 802.1Q header or with an 802.1Q header with a PCP of 0. Only
possible with NXM.
[10] Matches packets with no 802.1Q header or with an 802.1Q header with both VID and PCP of 0.
Only possible with NXM.
LAYER 2.5: MPLS FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
─────────── ──────────────── ───── ──── ──────── ──────────────────────
mpls_label 4 (low 20 bits) no yes MPLS OF 1.2+ and OVS 1.11+
mpls_tc 1 (low 3 bits) no yes MPLS OF 1.2+ and OVS 1.11+
mpls_bos 1 (low 1 bits) no no MPLS OF 1.3+ and OVS 1.11+
mpls_ttl 1 no yes MPLS OVS 2.6+
One or more MPLS headers (more commonly called MPLS labels) follow an Ethernet type field that specifies
an MPLS Ethernet type [RFC 3032]. Ethertype 0x8847 is used for all unicast. Multicast MPLS is divided
into two specific classes, one of which uses Ethertype 0x8847 and the other 0x8848 [RFC 5332].
The most common overall packet format is Ethernet II, shown below (SNAP encapsulation may be used but is
not ordinarily seen in Ethernet networks):
Ethernet MPLS
<------------> <------------>
48 48 16 20 3 1 8
+---+---+------+ +-----+--+-+---+
|dst|src| type | |label|TC|S|TTL| ...
+---+---+------+ +-----+--+-+---+
0x8847
MPLS can be encapsulated inside an 802.1Q header, in which case the combination looks like this:
Ethernet 802.1Q Ethertype MPLS
<------> <--------> <-------> <------------>
48 48 16 16 16 20 3 1 8
+----+---+ +------+---+ +---------+ +-----+--+-+---+
|dst |src| | TPID |TCI| | type | |label|TC|S|TTL| ...
+----+---+ +------+---+ +---------+ +-----+--+-+---+
0x8100 0x8847
The fields within an MPLS label are:
Label, 20 bits.
An identifier.
Traffic control (TC), 3 bits.
Used for quality of service.
Bottom of stack (BOS), 1 bit (labeled just ``S’’ above).
0 indicates that another MPLS label follows this one.
1 indicates that this MPLS label is the last one in the stack, so that some other protocol
follows this one.
Time to live (TTL), 8 bits.
Each hop across an MPLS network decrements the TTL by 1. If it reaches 0, the packet is
discarded.
OpenFlow does not make the MPLS TTL available as a match field, but actions are available
to set and decrement the TTL. Open vSwitch 2.6 and later makes the MPLS TTL available as an
extension.
MPLS Label Stacks
Unlike the other encapsulations supported by OpenFlow and Open vSwitch, MPLS labels are routinely used in
``stacks’’ two or three deep and sometimes even deeper. Open vSwitch currently supports up to three
labels.
The OpenFlow specification only supports matching on the outermost MPLS label at any given time. To match
on the second label, one must first ``pop’’ the outer label and advance to another OpenFlow table, where
the inner label may be matched. To match on the third label, one must pop the two outer labels, and so
on.
MPLS Inner Protocol
Unlike all other forms of encapsulation that Open vSwitch and OpenFlow support, an MPLS label does not
indicate what inner protocol it encapsulates. Different deployments determine the inner protocol in
different ways [RFC 3032]:
• A few reserved label values do indicate an inner protocol. Label 0, the ``IPv4 Explicit
NULL Label,’’ indicates inner IPv4. Label 2, the ``IPv6 Explicit NULL Label,’’ indicates
inner IPv6.
• Some deployments use a single inner protocol consistently.
• In some deployments, the inner protocol must be inferred from the innermost label.
• In some deployments, the inner protocol must be inferred from the innermost label and the
encapsulated data, e.g. to distinguish between inner IPv4 and IPv6 based on whether the
first nibble of the inner protocol data are 4 or 6. OpenFlow and Open vSwitch do not
currently support these cases.
Open vSwitch and OpenFlow do not infer the inner protocol, even if reserved label values are in use.
Instead, the flow table must specify the inner protocol at the time it pops the bottommost MPLS label,
using the Ethertype argument to the pop_mpls action.
Field Details
MPLS Label Field
Name: mpls_label
Width: 32 bits (only the least-significant 20 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_MPLS_LABEL (34) since OpenFlow 1.2 and Open vSwitch 1.11
NXM: none
The least significant 20 bits hold the ``label’’ field from the MPLS label. Other bits are zero:
OXM_OF_MPLS_LABEL
<--------------->
12 20
+--------+--------+
| zero | label |
+--------+--------+
0
Most label values are available for any use by deployments. Values under 16 are reserved.
MPLS Traffic Class Field
Name: mpls_tc
Width: 8 bits (only the least-significant 3 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_MPLS_TC (35) since OpenFlow 1.2 and Open vSwitch 1.11
NXM: none
The least significant 3 bits hold the TC field from the MPLS label. Other bits are zero:
OXM_OF_MPLS_TC
<------------>
5 3
+--------+-----+
| zero | TC |
+--------+-----+
0
This field is intended for use for Quality of Service (QoS) and Explicit Congestion Notification
purposes, but its particular interpretation is deployment specific.
Before 2009, this field was named EXP and reserved for experimental use [RFC 5462].
MPLS Bottom of Stack Field
Name: mpls_bos
Width: 8 bits (only the least-significant 1 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_MPLS_BOS (36) since OpenFlow 1.3 and Open vSwitch 1.11
NXM: none
The least significant bit holds the BOS field from the MPLS label. Other bits are zero:
OXM_OF_MPLS_BOS
<------------->
7 1
+--------+------+
| zero | BOS |
+--------+------+
0
This field is useful as part of processing a series of incoming MPLS labels. A flow that includes a
pop_mpls action should generally match on mpls_bos:
• When mpls_bos is 0, there is another MPLS label following this one, so the Ethertype passed
to pop_mpls should be an MPLS Ethertype. For example: table=0, dl_type=0x8847, mpls_bos=0,
actions=pop_mpls:0x8847, goto_table:1
• When mpls_bos is 1, this MPLS label is the last one, so the Ethertype passed to pop_mpls
should be a non-MPLS Ethertype such as IPv4. For example: table=1, dl_type=0x8847,
mpls_bos=1, actions=pop_mpls:0x0800, goto_table:2
MPLS Time-to-Live Field
Name: mpls_ttl
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_MPLS_TTL (30) since Open vSwitch 2.6
Holds the 8-bit time-to-live field from the MPLS label:
NXM_NX_MPLS_TTL
<------------->
8
+---------------+
| TTL |
+---------------+
LAYER 3: IPV4 AND IPV6 FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
────────────────────── ──────────────── ───── ──── ────────── ─────────────────────
ip_src aka nw_src 4 yes yes IPv4 OF 1.2+ and OVS 1.1+
ip_dst aka nw_dst 4 yes yes IPv4 OF 1.2+ and OVS 1.1+
ipv6_src 16 yes yes IPv6 OF 1.2+ and OVS 1.1+
ipv6_dst 16 yes yes IPv6 OF 1.2+ and OVS 1.1+
ipv6_label 4 (low 20 bits) yes yes IPv6 OF 1.2+ and OVS 1.4+
nw_proto aka ip_proto 1 no no IPv4/IPv6 OF 1.2+ and OVS 1.1+
nw_ttl 1 no yes IPv4/IPv6 OVS 1.4+
ip_frag aka nw_frag 1 (low 2 bits) yes no IPv4/IPv6 OVS 1.3+
nw_tos 1 no yes IPv4/IPv6 OVS 1.1+
ip_dscp 1 (low 6 bits) no yes IPv4/IPv6 OF 1.2+ and OVS 1.7+
nw_ecn aka ip_ecn 1 (low 2 bits) no yes IPv4/IPv6 OF 1.2+ and OVS 1.4+
IPv4 Specific Fields
These fields are applicable only to IPv4 flows, that is, flows that match on the IPv4 Ethertype 0x0800.
IPv4 Source Address Field
Name: ip_src (aka nw_src)
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: IPv4
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_IPV4_SRC (11) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_IP_SRC (7) since Open vSwitch 1.1
The source address from the IPv4 header:
Ethernet IPv4
<-----------> <--------------->
48 48 16 8 32 32
+---+---+-----+ +---+-----+---+---+
|dst|src|type | |...|proto|src|dst| ...
+---+---+-----+ +---+-----+---+---+
0x800
For historical reasons, in an ARP or RARP flow, Open vSwitch interprets matches on nw_src as actually
referring to the ARP SPA.
IPv4 Destination Address Field
Name: ip_dst (aka nw_dst)
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: IPv4
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_IPV4_DST (12) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_IP_DST (8) since Open vSwitch 1.1
The destination address from the IPv4 header:
Ethernet IPv4
<-----------> <--------------->
48 48 16 8 32 32
+---+---+-----+ +---+-----+---+---+
|dst|src|type | |...|proto|src|dst| ...
+---+---+-----+ +---+-----+---+---+
0x800
For historical reasons, in an ARP or RARP flow, Open vSwitch interprets matches on nw_dst as actually
referring to the ARP TPA.
IPv6 Specific Fields
These fields apply only to IPv6 flows, that is, flows that match on the IPv6 Ethertype 0x86dd.
IPv6 Source Address Field
Name: ipv6_src
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_SRC (26) since OpenFlow 1.2 and Open vSwitch 1.1
NXM: NXM_NX_IPV6_SRC (19) since Open vSwitch 1.1
The source address from the IPv6 header:
Ethernet IPv6
<------------> <-------------->
48 48 16 8 128 128
+---+---+------+ +---+----+---+---+
|dst|src| type | |...|next|src|dst| ...
+---+---+------+ +---+----+---+---+
0x86dd
Open vSwitch 1.8 added support for bitwise matching; earlier versions supported only CIDR masks.
IPv6 Destination Address Field
Name: ipv6_dst
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_DST (27) since OpenFlow 1.2 and Open vSwitch 1.1
NXM: NXM_NX_IPV6_DST (20) since Open vSwitch 1.1
The destination address from the IPv6 header:
Ethernet IPv6
<------------> <-------------->
48 48 16 8 128 128
+---+---+------+ +---+----+---+---+
|dst|src| type | |...|next|src|dst| ...
+---+---+------+ +---+----+---+---+
0x86dd
Open vSwitch 1.8 added support for bitwise matching; earlier versions supported only CIDR masks.
IPv6 Flow Label Field
Name: ipv6_label
Width: 32 bits (only the least-significant 20 bits may be nonzero)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_FLABEL (28) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_IPV6_LABEL (27) since Open vSwitch 1.4
The least significant 20 bits hold the flow label field from the IPv6 header. Other bits are zero:
OXM_OF_IPV6_FLABEL
<---------------->
12 20
+--------+---------+
| zero | label |
+--------+---------+
0
IPv4/IPv6 Fields
These fields exist with at least approximately the same meaning in both IPv4 and IPv6, so they are
treated as a single field for matching purposes. Any flow that matches on the IPv4 Ethertype 0x0800 or
the IPv6 Ethertype 0x86dd may match on these fields.
IPv4/v6 Protocol Field
Name: nw_proto (aka ip_proto)
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read-only
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IP_PROTO (10) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_IP_PROTO (6) since Open vSwitch 1.1
Matches the IPv4 or IPv6 protocol type.
For historical reasons, in an ARP or RARP flow, Open vSwitch interprets matches on nw_proto as actually
referring to the ARP opcode. The ARP opcode is a 16-bit field, so for matching purposes ARP opcodes
greater than 255 are treated as 0; this works adequately because in practice ARP and RARP only use
opcodes 1 through 4.
In the case of fragmented traffic, a difference exists in the way the field acts for IPv4 and IPv6 later
fragments. For IPv6 fragments with nonzero offset, nw_proto is set to the IPv6 protocol type for
fragments (44). Conversely, for IPv4 later fragments, the field is set based on the protocol type present
in the header.
IPv4/v6 TTL/Hop Limit Field
Name: nw_ttl
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_IP_TTL (29) since Open vSwitch 1.4
The main reason to match on the TTL or hop limit field is to detect whether a dec_ttl action will fail
due to a TTL exceeded error. Another way that a controller can detect TTL exceeded is to listen for
OFPR_INVALID_TTL ``packet-in’’ messages via OpenFlow.
IPv4/v6 Fragment Bitmask Field
Name: ip_frag (aka nw_frag)
Width: 8 bits (only the least-significant 2 bits may be nonzero)
Format: frag
Masking: arbitrary bitwise masks
Prerequisites: IPv4/IPv6
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_IP_FRAG (26) since Open vSwitch 1.3
Specifies what kinds of IP fragments or non-fragments to match. The value for this field is most
conveniently specified as one of the following:
no Match only non-fragmented packets.
yes Matches all fragments.
first Matches only fragments with offset 0.
later Matches only fragments with nonzero offset.
not_later
Matches non-fragmented packets and fragments with zero offset.
The field is internally formatted as 2 bits: bit 0 is 1 for an IP fragment with any offset (and otherwise
0), and bit 1 is 1 for an IP fragment with nonzero offset (and otherwise 0), like so:
NXM_NX_IP_FRAG
<------------>
6 1 1
+----+-----+---+
|zero|later|any|
+----+-----+---+
0
Even though 2 bits have 4 possible values, this field only uses 3 of them:
• A packet that is not an IP fragment has value 0.
• A packet that is an IP fragment with offset 0 (the first fragment) has bit 0 set and thus
value 1.
• A packet that is an IP fragment with nonzero offset has bits 0 and 1 set and thus value 3.
The switch may reject matches against values that can never appear.
It is important to understand how this field interacts with the OpenFlow fragment handling mode:
• In OFPC_FRAG_DROP mode, the OpenFlow switch drops all IP fragments before they reach the
flow table, so every packet that is available for matching will have value 0 in this field.
• Open vSwitch does not implement OFPC_FRAG_REASM mode, but if it did then IP fragments would
be reassembled before they reached the flow table and again every packet available for
matching would always have value 0.
• In OFPC_FRAG_NORMAL mode, all three values are possible, but OpenFlow 1.0 says that
fragments’ transport ports are always 0, even for the first fragment, so this does not
provide much extra information.
• In OFPC_FRAG_NX_MATCH mode, all three values are possible. For fragments with offset 0,
Open vSwitch makes L4 header information available.
Thus, this field is likely to be most useful for an Open vSwitch switch configured in OFPC_FRAG_NX_MATCH
mode. See the description of the set-frags command in ovs-ofctl(8), for more details.
IPv4/IPv6 TOS Fields
IPv4 and IPv6 contain a one-byte ``type of service’’ or TOS field that has the following format:
type of service
<------------->
6 2
+--------+------+
| DSCP | ECN |
+--------+------+
IPv4/v6 DSCP (Bits 2-7) Field
Name: nw_tos
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: none
NXM: NXM_OF_IP_TOS (5) since Open vSwitch 1.1
This field is the TOS byte with the two ECN bits cleared to 0:
NXM_OF_IP_TOS
<----------->
6 2
+------+------+
| DSCP | zero |
+------+------+
0
IPv4/v6 DSCP (Bits 0-5) Field
Name: ip_dscp
Width: 8 bits (only the least-significant 6 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IP_DSCP (8) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: none
This field is the TOS byte shifted right to put the DSCP bits in the 6 least-significant bits:
OXM_OF_IP_DSCP
<------------>
2 6
+-------+------+
| zero | DSCP |
+-------+------+
0
IPv4/v6 ECN Field
Name: nw_ecn (aka ip_ecn)
Width: 8 bits (only the least-significant 2 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IP_ECN (9) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_IP_ECN (28) since Open vSwitch 1.4
This field is the TOS byte with the DSCP bits cleared to 0:
OXM_OF_IP_ECN
<----------->
6 2
+-------+-----+
| zero | ECN |
+-------+-----+
0
LAYER 3: ARP FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────── ────── ───── ──── ──────── ─────────────────────
arp_op 2 no yes ARP OF 1.2+ and OVS 1.1+
arp_spa 4 yes yes ARP OF 1.2+ and OVS 1.1+
arp_tpa 4 yes yes ARP OF 1.2+ and OVS 1.1+
arp_sha 6 yes yes ARP OF 1.2+ and OVS 1.1+
arp_tha 6 yes yes ARP OF 1.2+ and OVS 1.1+
In theory, Address Resolution Protocol, or ARP, is a generic protocol generic protocol that can be used
to obtain the hardware address that corresponds to any higher-level protocol address. In contemporary
usage, ARP is used only in Ethernet networks to obtain the Ethernet address for a given IPv4 address.
OpenFlow and Open vSwitch only support this usage of ARP. For this use case, an ARP packet has the
following format, with the ARP fields exposed as Open vSwitch fields highlighted:
Ethernet ARP
<-----------> <---------------------------------->
48 48 16 16 16 8 8 16 48 32 48 32
+---+---+-----+ +---+-----+---+---+--+---+---+---+---+
|dst|src|type | |hrd| pro |hln|pln|op|sha|spa|tha|tpa|
+---+---+-----+ +---+-----+---+---+--+---+---+---+---+
0x806 1 0x800 6 4
The ARP fields are also used for RARP, the Reverse Address Resolution Protocol, which shares ARP’s wire
format.
ARP Opcode Field
Name: arp_op
Width: 16 bits
Format: decimal
Masking: not maskable
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ARP_OP (21) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ARP_OP (15) since Open vSwitch 1.1
Even though this is a 16-bit field, Open vSwitch does not support ARP opcodes greater than 255; it treats
them to zero. This works adequately because in practice ARP and RARP only use opcodes 1 through 4.
ARP Source IPv4 Address Field
Name: arp_spa
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ARP_SPA (22) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ARP_SPA (16) since Open vSwitch 1.1
ARP Target IPv4 Address Field
Name: arp_tpa
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ARP_TPA (23) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ARP_TPA (17) since Open vSwitch 1.1
ARP Source Ethernet Address Field
Name: arp_sha
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ARP_SHA (24) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ARP_SHA (17) since Open vSwitch 1.1
ARP Target Ethernet Address Field
Name: arp_tha
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ARP_THA (25) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ARP_THA (18) since Open vSwitch 1.1
LAYER 3: NSH FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────────────── ──────────────── ───── ──── ──────── ────────────────
nsh_flags 1 yes yes NSH OVS 2.8+
nsh_ttl 1 no yes NSH OVS 2.9+
nsh_mdtype 1 no no NSH OVS 2.8+
nsh_np 1 no no NSH OVS 2.8+
nsh_spi aka nsp 4 (low 24 bits) no yes NSH OVS 2.8+
nsh_si aka nsi 1 no yes NSH OVS 2.8+
nsh_c1 aka nshc1 4 yes yes NSH OVS 2.8+
nsh_c2 aka nshc2 4 yes yes NSH OVS 2.8+
nsh_c3 aka nshc3 4 yes yes NSH OVS 2.8+
nsh_c4 aka nshc4 4 yes yes NSH OVS 2.8+
Service functions are widely deployed and essential in many networks. These service functions provide a
range of features such as security, WAN acceleration, and server load balancing. Service functions may be
instantiated at different points in the network infrastructure such as the wide area network, data
center, and so forth.
Prior to development of the SFC architecture [RFC 7665] and the protocol specified in this document,
current service function deployment models have been relatively static and bound to topology for
insertion and policy selection. Furthermore, they do not adapt well to elastic service environments
enabled by virtualization.
New data center network and cloud architectures require more flexible service function deployment models.
Additionally, the transition to virtual platforms demands an agile service insertion model that supports
dynamic and elastic service delivery. Specifically, the following functions are necessary:
1. The movement of service functions and application workloads in the network.
2. The ability to easily bind service policy to granular information, such as per-subscriber
state.
3. The capability to steer traffic to the requisite service function(s).
The Network Service Header (NSH) specification defines a new data plane protocol, which is an
encapsulation for service function chains. The NSH is designed to encapsulate an original packet or
frame, and in turn be encapsulated by an outer transport encapsulation (which is used to deliver the NSH
to NSH-aware network elements), as shown below:
+-----------------------+----------------------------+---------------------+
|Transport Encapsulation|Network Service Header (NSH)|Original Packet/Frame|
+-----------------------+----------------------------+---------------------+
The NSH is composed of the following elements:
1. Service Function Path identification.
2. Indication of location within a Service Function Path.
3. Optional, per packet metadata (fixed length or variable).
[RFC 7665] provides an overview of a service chaining architecture that clearly defines the roles of the
various elements and the scope of a service function chaining encapsulation. Figure 3 of [RFC 7665]
depicts the SFC architectural components after classification. The NSH is the SFC encapsulation
referenced in [RFC 7665].
flags field (2 bits) Field
Name: nsh_flags
Width: 8 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_FLAGS (1) since Open vSwitch 2.8
TTL field (6 bits) Field
Name: nsh_ttl
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_TTL (10) since Open vSwitch 2.9
mdtype field (8 bits) Field
Name: nsh_mdtype
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_MDTYPE (2) since Open vSwitch 2.8
np (next protocol) field (8 bits) Field
Name: nsh_np
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_NP (3) since Open vSwitch 2.8
spi (service path identifier) field (24 bits) Field
Name: nsh_spi (aka nsp)
Width: 32 bits (only the least-significant 24 bits may be nonzero)
Format: hexadecimal
Masking: not maskable
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_SPI (4) since Open vSwitch 2.8
si (service index) field (8 bits) Field
Name: nsh_si (aka nsi)
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_SI (5) since Open vSwitch 2.8
c1 (Network Platform Context) field (32 bits) Field
Name: nsh_c1 (aka nshc1)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C1 (6) since Open vSwitch 2.8
c2 (Network Shared Context) field (32 bits) Field
Name: nsh_c2 (aka nshc2)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C2 (7) since Open vSwitch 2.8
c3 (Service Platform Context) field (32 bits) Field
Name: nsh_c3 (aka nshc3)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C3 (8) since Open vSwitch 2.8
c4 (Service Shared Context) field (32 bits) Field
Name: nsh_c4 (aka nshc4)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C4 (9) since Open vSwitch 2.8
LAYER 4: TCP, UDP, AND SCTP FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
─────────────────── ──────────────── ───── ──── ──────── ─────────────────────
tcp_src aka tp_src 2 yes yes TCP OF 1.2+ and OVS 1.1+
tcp_dst aka tp_dst 2 yes yes TCP OF 1.2+ and OVS 1.1+
tcp_flags 2 (low 12 bits) yes no TCP OF 1.3+ and OVS 2.1+
udp_src 2 yes yes UDP OF 1.2+ and OVS 1.1+
udp_dst 2 yes yes UDP OF 1.2+ and OVS 1.1+
sctp_src 2 yes yes SCTP OF 1.2+ and OVS 2.0+
sctp_dst 2 yes yes SCTP OF 1.2+ and OVS 2.0+
For matching purposes, no distinction is made whether these protocols are encapsulated within IPv4 or
IPv6.
TCP
The following diagram shows TCP within IPv4. Open vSwitch also supports TCP in IPv6. Only TCP fields
implemented as Open vSwitch fields are shown:
Ethernet IPv4 TCP
<-----------> <---------------> <------------------->
48 48 16 8 32 32 16 16 12
+---+---+-----+ +---+-----+---+---+ +---+---+---+-----+---+
|dst|src|type | |...|proto|src|dst| |src|dst|...|flags|...| ...
+---+---+-----+ +---+-----+---+---+ +---+---+---+-----+---+
0x800 6
TCP Source Port Field
Name: tcp_src (aka tp_src)
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: TCP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_TCP_SRC (13) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_TCP_SRC (9) since Open vSwitch 1.1
Open vSwitch 1.6 added support for bitwise matching.
TCP Destination Port Field
Name: tcp_dst (aka tp_dst)
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: TCP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_TCP_DST (14) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_TCP_DST (10) since Open vSwitch 1.1
Open vSwitch 1.6 added support for bitwise matching.
TCP Flags Field
Name: tcp_flags
Width: 16 bits (only the least-significant 12 bits may be nonzero)
Format: TCP flags
Masking: arbitrary bitwise masks
Prerequisites: TCP
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: ONFOXM_ET_TCP_FLAGS (42) since OpenFlow 1.3 and Open vSwitch 2.4; OXM_OF_TCP_FLAGS (42)
since OpenFlow 1.5 and Open vSwitch 2.3
NXM: NXM_NX_TCP_FLAGS (34) since Open vSwitch 2.1
This field holds the TCP flags. TCP currently defines 9 flag bits. An additional 3 bits are reserved. For
more information, see [RFC 793], [RFC 3168], and [RFC 3540].
Matches on this field are most conveniently written in terms of symbolic names (given in the diagram
below), each preceded by either + for a flag that must be set, or - for a flag that must be unset,
without any other delimiters between the flags. Flags not mentioned are wildcarded. For example,
tcp,tcp_flags=+syn-ack matches TCP SYNs that are not ACKs, and tcp,tcp_flags=+[200] matches TCP packets
with the reserved [200] flag set. Matches can also be written as flags/mask, where flags and mask are
16-bit numbers in decimal or in hexadecimal prefixed by 0x.
The flag bits are:
reserved later RFCs RFC 793
<---------------> <--------> <--------------------->
4 1 1 1 1 1 1 1 1 1 1 1 1
+----+-----+-----+-----+--+---+---+---+---+---+---+---+---+
|zero|[800]|[400]|[200]|NS|CWR|ECE|URG|ACK|PSH|RST|SYN|FIN|
+----+-----+-----+-----+--+---+---+---+---+---+---+---+---+
0
UDP
The following diagram shows UDP within IPv4. Open vSwitch also supports UDP in IPv6. Only UDP fields that
Open vSwitch exposes as fields are shown:
Ethernet IPv4 UDP
<-----------> <---------------> <--------->
48 48 16 8 32 32 16 16
+---+---+-----+ +---+-----+---+---+ +---+---+---+
|dst|src|type | |...|proto|src|dst| |src|dst|...| ...
+---+---+-----+ +---+-----+---+---+ +---+---+---+
0x800 17
UDP Source Port Field
Name: udp_src
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: UDP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_UDP_SRC (15) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_UDP_SRC (11) since Open vSwitch 1.1
UDP Destination Port Field
Name: udp_dst
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: UDP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_UDP_DST (16) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_UDP_DST (12) since Open vSwitch 1.1
SCTP
The following diagram shows SCTP within IPv4. Open vSwitch also supports SCTP in IPv6. Only SCTP fields
that Open vSwitch exposes as fields are shown:
Ethernet IPv4 SCTP
<-----------> <---------------> <--------->
48 48 16 8 32 32 16 16
+---+---+-----+ +---+-----+---+---+ +---+---+---+
|dst|src|type | |...|proto|src|dst| |src|dst|...| ...
+---+---+-----+ +---+-----+---+---+ +---+---+---+
0x800 132
SCTP Source Port Field
Name: sctp_src
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: SCTP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_SCTP_SRC (17) since OpenFlow 1.2 and Open vSwitch 2.0
NXM: none
SCTP Destination Port Field
Name: sctp_dst
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: SCTP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_SCTP_DST (18) since OpenFlow 1.2 and Open vSwitch 2.0
NXM: none
LAYER 4: ICMPV4 AND ICMPV6 FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────────────── ────── ───── ──── ─────────── ─────────────────────
icmp_type 1 no yes ICMPv4 OF 1.2+ and OVS 1.1+
icmp_code 1 no yes ICMPv4 OF 1.2+ and OVS 1.1+
icmpv6_type 1 no yes ICMPv6 OF 1.2+ and OVS 1.1+
icmpv6_code 1 no yes ICMPv6 OF 1.2+ and OVS 1.1+
nd_target 16 yes yes ND OF 1.2+ and OVS 1.1+
nd_sll 6 yes yes ND solicit OF 1.2+ and OVS 1.1+
nd_tll 6 yes yes ND advert OF 1.2+ and OVS 1.1+
nd_reserved 4 no yes ND OVS 2.11+
nd_options_type 1 no yes ND OVS 2.11+
ICMPv4
Ethernet IPv4 ICMPv4
<-----------> <---------------> <----------->
48 48 16 8 32 32 8 8
+---+---+-----+ +---+-----+---+---+ +----+----+---+
|dst|src|type | |...|proto|src|dst| |type|code|...| ...
+---+---+-----+ +---+-----+---+---+ +----+----+---+
0x800 1
ICMPv4 Type Field
Name: icmp_type
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv4
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ICMPV4_TYPE (19) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ICMP_TYPE (13) since Open vSwitch 1.1
For historical reasons, in an ICMPv4 flow, Open vSwitch interprets matches on tp_src as actually
referring to the ICMP type.
ICMPv4 Code Field
Name: icmp_code
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv4
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ICMPV4_CODE (20) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_OF_ICMP_CODE (14) since Open vSwitch 1.1
For historical reasons, in an ICMPv4 flow, Open vSwitch interprets matches on tp_dst as actually
referring to the ICMP code.
ICMPv6
Ethernet IPv6 ICMPv6
<------------> <--------------> <----------->
48 48 16 8 128 128 8 8
+---+---+------+ +---+----+---+---+ +----+----+---+
|dst|src| type | |...|next|src|dst| |type|code|...| ...
+---+---+------+ +---+----+---+---+ +----+----+---+
0x86dd 58
ICMPv6 Type Field
Name: icmpv6_type
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ICMPV6_TYPE (29) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ICMPV6_TYPE (21) since Open vSwitch 1.1
ICMPv6 Code Field
Name: icmpv6_code
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ICMPV6_CODE (30) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ICMPV6_CODE (22) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery
Ethernet IPv6 ICMPv6 ICMPv6 ND
<------------> <--------------> <--------------> <--------------->
48 48 16 8 128 128 8 8 128
+---+---+------+ +---+----+---+---+ +-------+----+---+ +------+----------+
|dst|src| type | |...|next|src|dst| | type |code|...| |target|option ...|
+---+---+------+ +---+----+---+---+ +-------+----+---+ +------+----------+
0x86dd 58 135/136 0
ICMPv6 Neighbor Discovery Target IPv6 Field
Name: nd_target
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: ND
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_ND_TARGET (31) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ND_TARGET (23) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery Source Ethernet Address Field
Name: nd_sll
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ND solicit
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_ND_SLL (32) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ND_SLL (24) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery Target Ethernet Address Field
Name: nd_tll
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ND advert
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_ND_TLL (33) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_ND_TLL (25) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery Reserved Field Field
Name: nd_reserved
Width: 32 bits
Format: decimal
Masking: not maskable
Prerequisites: ND
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: ERICOXM_OF_ICMPV6_ND_RESERVED (1) since Open vSwitch 2.11
This is used to set the R,S,O bits in Neighbor Advertisement Messages
ICMPv6 Neighbor Discovery Options Type Field Field
Name: nd_options_type
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ND
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: ERICOXM_OF_ICMPV6_ND_OPTIONS_TYPE (2) since Open vSwitch 2.11
A value of 1 indicates that the option is Source Link Layer. A value of 2 indicates that the options is
Target Link Layer. See RFC 4861 for further details.
REFERENCES
Casado M. Casado, M. J. Freedman, J. Pettit, J. Luo, N. McKeown, and S. Shenker, ``Ethane: Taking
Control of the Enterprise,’’ Computer Communications Review, October 2007.
ERSPAN M. Foschiano, K. Ghosh, M. Mehta, ``Cisco Systems’ Encapsulated Remote Switch Port Analyzer
(ERSPAN),’’ ⟨https://tools.ietf.org/html/draft-foschiano-erspan-03⟩ .
EXT-56 J. Tonsing, ``Permit one of a set of prerequisites to apply, e.g. don’t preclude non-
Ethernet media,’’ ⟨https://rs.opennetworking.org/bugs/browse/EXT-56⟩ (ONF members only).
EXT-112
J. Tourrilhes, ``Support non-Ethernet packets throughout the pipeline,’’ ⟨https://
rs.opennetworking.org/bugs/browse/EXT-112⟩ (ONF members only).
EXT-134
J. Tourrilhes, ``Match first nibble of the MPLS payload,’’ ⟨https://rs.opennetworking.org/
bugs/browse/EXT-134⟩ (ONF members only).
Geneve J. Gross, I. Ganga, and T. Sridhar, editors, ``Geneve: Generic Network Virtualization
Encapsulation,’’ ⟨https://datatracker.ietf.org/doc/draft-ietf-nvo3-geneve/⟩ .
IEEE OUI
IEEE Standards Association, ``MAC Address Block Large (MA-L),’’ ⟨https://
standards.ieee.org/develop/regauth/oui/index.html⟩ .
NSH P. Quinn and U. Elzur, editors, ``Network Service Header,’’ ⟨https://datatracker.ietf.org/
doc/draft-ietf-sfc-nsh/⟩ .
OpenFlow 1.0.1
Open Networking Foundation, ``OpenFlow Switch Errata, Version 1.0.1,’’ June 2012.
OpenFlow 1.1
OpenFlow Consortium, ``OpenFlow Switch Specification Version 1.1.0 Implemented (Wire
Protocol 0x02),’’ February 2011.
OpenFlow 1.5
Open Networking Foundation, ``OpenFlow Switch Specification Version 1.5.0 (Protocol version
0x06),’’ December 2014.
OpenFlow Extensions 1.3.x Package 2
Open Networking Foundation, ``OpenFlow Extensions 1.3.x Package 2,’’ December 2013.
TCP Flags Match Field Extension
Open Networking Foundation, ``TCP flags match field Extension,’’ December 2014. In
[OpenFlow Extensions 1.3.x Package 2].
Pepelnjak
I. Pepelnjak, ``OpenFlow and Fermi Estimates,’’ ⟨http://blog.ipspace.net/2013/09/
openflow-and-fermi-estimates.html⟩ .
RFC 793
``Transmission Control Protocol,’’ ⟨http://www.ietf.org/rfc/rfc793.txt⟩ .
RFC 3032
E. Rosen, D. Tappan, G. Fedorkow, Y. Rekhter, D. Farinacci, T. Li, and A. Conta, ``MPLS
Label Stack Encoding,’’ ⟨http://www.ietf.org/rfc/rfc3032.txt⟩ .
RFC 3168
K. Ramakrishnan, S. Floyd, and D. Black, ``The Addition of Explicit Congestion Notification
(ECN) to IP,’’ ⟨https://tools.ietf.org/html/rfc3168⟩ .
RFC 3540
N. Spring, D. Wetherall, and D. Ely, ``Robust Explicit Congestion Notification (ECN)
Signaling with Nonces,’’ ⟨https://tools.ietf.org/html/rfc3540⟩ .
RFC 4632
V. Fuller and T. Li, ``Classless Inter-domain Routing (CIDR): The Internet Address
Assignment and Aggregation Plan,’’ ⟨https://tools.ietf.org/html/rfc4632⟩ .
RFC 5462
L. Andersson and R. Asati, ``Multiprotocol Label Switching (MPLS) Label Stack Entry:
``EXP’’ Field Renamed to ``Traffic Class’’ Field,’’ ⟨http://www.ietf.org/rfc/rfc5462.txt⟩ .
RFC 6830
D. Farinacci, V. Fuller, D. Meyer, and D. Lewis, ``The Locator/ID Separation Protocol
(LISP),’’ ⟨http://www.ietf.org/rfc/rfc6830.txt⟩ .
RFC 7348
M. Mahalingam, D. Dutt, K. Duda, P. Agarwal, L. Kreeger, T. Sridhar, M. Bursell, and C.
Wright, ``Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying
Virtualized Layer 2 Networks over Layer 3 Networks, ’’ ⟨https://tools.ietf.org/html/
rfc7348⟩ .
RFC 7665
J. Halpern, Ed. and C. Pignataro, Ed., ``Service Function Chaining (SFC) Architecture,’’
⟨https://tools.ietf.org/html/rfc7665⟩ .
Srinivasan
V. Srinivasan, S. Suriy, and G. Varghese, ``Packet Classification using Tuple Space
Search,’’ SIGCOMM 1999.
Pagiamtzis
K. Pagiamtzis and A. Sheikholeslami, ``Content-addressable memory (CAM) circuits and
architectures: A tutorial and survey,’’ IEEE Journal of Solid-State Circuits, vol. 41, no.
3, pp. 712-727, March 2006.
VXLAN Group Policy Option
M. Smith and L. Kreeger, `` VXLAN Group Policy Option.’’ Internet-Draft. ⟨https://
tools.ietf.org/html/draft-smith-vxlan-group-policy⟩ .
AUTHORS
Ben Pfaff, with advice from Justin Pettit and Jean Tourrilhes.