Provided by: openvswitch-common_3.4.0-1build1_amd64 
NAME
ovs-actions - OpenFlow actions and instructions with Open vSwitch extensions
INTRODUCTION
This document aims to comprehensively document all of the OpenFlow actions and
instructions, both standard and non-standard, supported by Open vSwitch, regardless of
origin. The document includes information of interest to Open vSwitch users, such as the
semantics of each supported action and the syntax used by Open vSwitch tools, and to
developers seeking to build controllers and switches compatible with Open vSwitch, such as
the wire format for each supported message.
Actions
In this document, we define an action as an OpenFlow action, which is a kind of command
that specifies what to do with a packet. Actions are used in OpenFlow flows to describe
what to do when the flow matches a packet, and in a few other places in OpenFlow. Each
version of the OpenFlow specification defines standard actions, and beyond that many
OpenFlow switches, including Open vSwitch, implement extensions to the standard.
OpenFlow groups actions in two ways: as an action list or an action set, described below.
Action Lists
An action list, a concept present in every version of OpenFlow, is simply an ordered
sequence of actions. The OpenFlow specifications require a switch to execute actions
within an action list in the order specified, and to refuse to execute an action list
entirely if it cannot implement the actions in that order [OpenFlow 1.0, section 3.3],
with one exception: when an action list outputs multiple packets, the switch may output
the packets in an order different from that specified. Usually, this exception is not
important, especially in the common case when the packets are output to different ports.
Action Sets
OpenFlow 1.1 introduced the concept of an action set. An action set is also a sequence of
actions, but the switch reorders the actions and drops duplicates according to rules
specified in the OpenFlow specifications. Because of these semantics, some standard
OpenFlow actions cannot usefully be included in an action set. For some, but not all,
Open vSwitch extension actions, Open vSwitch defines its own action set semantics and
ordering.
The OpenFlow pipeline has an action set associated with it as a packet is processed.
After pipeline processing is otherwise complete, the switch executes the actions in the
action set.
Open vSwitch applies actions in an action set in the following order: Except as noted
otherwise below, the action set only executes at most a single action of each type, and
when more than one action of a given type is present, the one added to the set later
replaces the earlier action:
1. strip_vlan
2. pop_mpls
3. decap
4. encap
5. push_mpls
6. push_vlan
7. dec_ttl
8. dec_mpls_ttl
9. dec_nsh_ttl
10. All of the following actions are executed in the order added to the action set,
with cumulative effect. That is, when multiple actions modify the same part of a
field, the later modification takes effect, and when they modify different parts of
a field (or different fields), then both modifications are applied:
• load
• move
• mod_dl_dst
• mod_dl_src
• mod_nw_dst
• mod_nw_src
• mod_nw_tos
• mod_nw_ecn
• mod_nw_ttl
• mod_tp_dst
• mod_tp_src
• mod_vlan_pcp
• mod_vlan_vid
• set_field
• set_tunnel
• set_tunnel64
11. set_queue
12. group, output, resubmit, ct_clear, or ct. If more than one of these actions is
present, then the one listed earliest above is executed and the others are ignored,
regardless of the order in which they were added to the action set. (If none of
these actions is present, the action set has no real effect, because the modified
packet is not sent anywhere and thus the modifications are not visible.)
An action set may only contain the actions listed above.
Error Handling
Packet processing can encounter a variety of errors:
Bridge not found
Open vSwitch supports an extension to the standard OpenFlow controller action
called a continuation, which allows the controller to interrupt and later resume
the processing of a packet through the switch pipeline. This error occurs when
such a packet’s processing cannot be resumed, e.g. because the bridge processing
it has been destroyed. Open vSwitch reports this error to the controller as Open
vSwitch extension error NXR_STALE.
This error prevents packet processing entirely.
Recursion too deep
While processing a given packet, Open vSwitch limits the flow table recursion depth
to 64, to ensure that packet processing uses a finite amount of time and space.
Actions that count against the recursion limit include resubmit from a given
OpenFlow table to the same or an earlier table, group, and output to patch ports.
A resubmit from one table to a later one (or, equivalently, a goto_table
instruction) does not count against the depth limit because resubmits to strictly
monotonically increasing tables will eventually terminate. OpenFlow tables are
most commonly traversed in numerically increasing order, so this limit has little
effect on conventionally designed OpenFlow pipelines.
This error terminates packet processing. Any previous side effects (e.g. output
actions) are retained.
Usually this error indicates a loop or other bug in the OpenFlow flow tables. To
assist debugging, when this error occurs, Open vSwitch 2.10 and later logs a trace
of the packet execution, as if by ovs-appctl ofproto/trace, rate-limited to one per
minute to reduce the log volume.
Too many resubmits
Open vSwitch limits the total number of resubmit actions that a given packet can
execute to 4,096. For this purpose, goto_table instructions and output to the
table port are treated like resubmit. This limits the amount of time to process a
single packet.
Unlike the limit on recursion depth, the limit on resubmits counts all resubmits,
regardless of direction.
This error has the same effect, including logging, as exceeding the recursion depth
limit.
Stack too deep
Open vSwitch limits the amount of data that the push action can put onto the stack
at one time to 64 kB of data.
This error terminates packet processing. Any previous side effects (e.g. output
actions) are retained.
No recirculation context / Recirculation conflict
These errors indicate internal errors inside Open vSwitch and should generally not
occur. If you notice recurring log messages about these errors, please report a
bug.
Too many MPLS labels
Open vSwitch can process packets with any number of MPLS labels, but its ability to
push and pop MPLS labels is limited, currently to 3 labels. Attempting to push
more than the supported number of labels onto a packet, or to pop any number of
labels from a packet with more than the supported number, raises this error.
This error terminates packet processing, retaining any previous side effects (e.g.
output actions). When this error arises within the execution of a group bucket, it
only terminates that bucket’s execution, not packet processing overall.
Invalid tunnel metadata
Open vSwitch raises this error when it processes a Geneve packet that has TLV
options with an invalid form, e.g. where the length in a TLV would extend past the
end of the options.
This error prevents packet processing entirely.
Unsupported packet type
When a encap action encapsulates a packet, Open vSwitch raises this error if it
does not support the combination of the new encapsulation with the current packet.
encap(ethernet) raises this error if the current packet is not an L3 packet, and
encap(nsh) raises this error if the current packet is not Ethernet, IPv4, IPv6, or
NSH.
The decap action is supported only for packet types ethernet, NSH and MPLS.
Openvswitch raises this error for other packet types. When a decap action
decapsulates a packet, Open vSwitch raises this error if it does not support the
type of inner packet. decap of an Ethernet header raises this error if a VLAN
header is present, decap of a NSH packet raises this error if the NSH inner packet
is not Ethernet, IPv4, IPv6, or NSH.
This error terminates packet processing, retaining any previous side effects (e.g.
output actions). When this error arises within the execution of a group bucket, it
only terminates that bucket’s execution, not packet processing overall.
Inconsistencies
OpenFlow 1.0 allows any action to be part of any flow, regardless of the flow’s match.
Some combinations do not make sense, e.g. an set_nw_tos action in a flow that matches only
ARP packets or strip_vlan in a flow that matches packets without VLAN tags. Other
combinations have varying results depending on the kind of packet that the flow processes,
e.g. a set_nw_src action in a flow that does not match on Ethertype will be treated as a
no-op when it processes a non-IPv4 packet. Nevertheless OVS allows all of the above in
conformance with OpenFlow 1.0, that is, the following will succeed:
$ ovs-ofctl -O OpenFlow10 add-flow br0 arp,actions=mod_nw_tos:12
$ ovs-ofctl -O OpenFlow10 add-flow br0 dl_vlan=0xffff,actions=strip_vlan
$ ovs-ofctl -O OpenFlow10 add-flow br0 actions=mod_nw_src:1.2.3.4
Open vSwitch calls these kinds of combinations inconsistencies between match and actions.
OpenFlow 1.1 and later forbid inconsistencies, and disallow the examples described above
by preventing such flows from being added. All of the above, for example, will fail with
an error message if one replaces OpenFlow10 by OpenFlow11.
OpenFlow 1.1 and later cannot detect and disallow all inconsistencies. For example, the
write_actions instruction arbitrarily delays execution of the actions inside it, which can
even be canceled with clear_actions, so that there is no way to ensure that its actions
are consistent with the packet at the time they execute. Thus, actions with write_actions
and some other contexts are exempt from consistency requirements.
When OVS executes an action inconsistent with the packet, it treats it as a no-op.
Inter-Version Compatibility
Open vSwitch supports multiple OpenFlow versions simultaneously on a single switch. When
actions are added with one OpenFlow version and then retrieved with another, Open vSwitch
does its best to translate between them.
Inter-version compatibility issues can still arise when different connections use
different OpenFlow versions. Backward compatibility is the most obvious case. Suppose,
for example, that an OpenFlow 1.1 session adds a flow with a push_vlan action, for which
there is no equivalent in OpenFlow 1.0. If an OpenFlow 1.0 session retrieves this flow,
Open vSwitch must somehow represent the action.
Forward compatibility can also be an issue, because later OpenFlow versions sometimes
remove functionality. The best example is the enqueue action from OpenFlow 1.0, which
OpenFlow 1.1 removed.
In practice, Open vSwitch uses a variety of strategies for inter-version compatibility:
• Most standard OpenFlow actions, such as output actions, translate without compatibility
issues.
• Open vSwitch supports its extension actions in every OpenFlow version, so they do not
pose inter-version compatibility problems.
• Open vSwitch sometimes adds extension actions to ensure backward or forward
compatibility. For example, for backward compatibility with the group action added in
OpenFlow 1.1, Open vSwitch includes an OpenFlow 1.0 extension group action.
Perfect inter-version compatibility is not possible, so best results require OpenFlow
connections to use a consistent version. One may enforce use of a particular version by
setting the protocols column for a bridge, e.g. to force br0 to use only OpenFlow 1.3:
ovs-vsctl set bridge br0 protocols=OpenFlow13
Field Specifications
Many Open vSwitch actions refer to fields. In such cases, fields may usually be referred
to by their common names, such as eth_dst for the Ethernet destination field, or by their
full OXM or NXM names, such as NXM_OF_ETH_DST or OXM_OF_ETH_DST. Before Open vSwitch 2.7,
only OXM or NXM field names were accepted.
Many actions that act on fields can also act on subfields, that is, parts of fields,
written as field[start..end], where start is the first bit and end is the last bit to use
in field, e.g. vlan_tci[13..15] for the VLAN PCP. A single-bit subfield may also be
written as field[offset], e.g. vlan_tci[13] for the least-significant bit of the VLAN PCP.
Empty brackets may be used to explicitly designate an entire field, e.g. vlan_tci[] for
the entire 16-bit VLAN TCI header. Before Open vSwitch 2.7, brackets were required in
field specifications.
See ovs-fields(7) for a list of fields and their names.
Port Specifications
Many Open vSwitch actions refer to OpenFlow ports. In such cases, the port may be
specified as a numeric port number in the range 0 to 65,535, although Open vSwitch only
assigns port numbers in the range 1 through 62,279 to ports. OpenFlow 1.1 and later use
32-bit port numbers, but Open vSwitch never assigns a port number that requires more than
16 bits.
In most contexts, the name of a port may also be used. (The most obvious context where a
port name may not be used is in an ovs-ofctl command along with the --no-names option.)
When a port’s name contains punctuation or could be ambiguous with other actions, the name
may be enclosed in double quotes, with JSON-like string escapes supported (see [RFC
8259]).
Open vSwitch also supports the following standard OpenFlow port names (even in contexts
where port names are not otherwise supported). The corresponding OpenFlow 1.0 and 1.1+
port numbers are listed alongside them but should not be used in flow syntax:
• in_port (65528 or 0xfff8; 0xfffffff8)
• table (65529 or 0xfff9; 0xfffffff9)
• normal (65530 or 0xfffa; 0xfffffffa)
• flood (65531 or 0xfffb; 0xfffffffb)
• all (65532 or 0xfffc; 0xfffffffc)
• controller (65533 or 0xfffd; 0xfffffffd)
• local (65534 or 0xfffe; 0xfffffffe)
• any or none (65535 or 0xffff; 0xffffffff)
• unset (not in OpenFlow 1.0; 0xfffffff7)
OUTPUT ACTIONS
These actions send a packet to a physical port or a controller. A packet that never
encounters an output action on its trip through the Open vSwitch pipeline is effectively
dropped. Because actions are executed in order, a packet modification action that is not
eventually followed by an output action will not have an externally visible effect.
The output action
Syntax:
port
output:port
output:field
output(port=port, max_len=nbytes)
Outputs the packet to an OpenFlow port most commonly specified as port. Alternatively,
the output port may be read from field, a field or subfield in the syntax described under
Field Specifications above. Either way, if the port is the packet’s input port, the
packet is not output.
The port may be one of the following standard OpenFlow ports:
local Outputs the packet on the local port that corresponds to the network device that
has the same name as the bridge, unless the packet was received on the local
port. OpenFlow switch implementations are not required to have a local port,
but Open vSwitch bridges always do.
in_port
Outputs the packet on the port on which it was received. This is the only
standard way to output the packet to the input port (but see Output to the Input
port, below).
The port may also be one of the following additional OpenFlow ports, unless max_len is
specified:
normal Subjects the packet to the device’s normal L2/L3 processing. This action is not
implemented by all OpenFlow switches, and each switch implements it differently.
The section The OVS Normal Pipeline below documents the OVS implementation.
flood Outputs the packet on all switch physical ports, except the port on which it was
received and any ports on which flooding is disabled. Flooding can be disabled
automatically on a port by Open vSwitch when IEEE 802.1D spanning tree (STP) or
rapid spanning tree (RSTP) is enabled, or by a controller using an OpenFlow
OFPT_MOD_PORT request to set the port’s OFPPC_NO_FLOOD flag (ovs-ofctl mod-port
provides a command-line interface to set this flag).
all Outputs the packet on all switch physical ports except the port on which it was
received.
controller
Sends the packet and its metadata to an OpenFlow controller or controllers
encapsulated in an OpenFlow packet-in message. The separate controller action,
described below, provides more options for output to a controller.
Open vSwitch rejects output to other standard OpenFlow ports, including none, unset, and
port numbers reserved for future use as standard ports, with the error
OFPBAC_BAD_OUT_PORT.
With max_len, the packet is truncated to at most nbytes bytes before being output. In
this case, the output port may not be a patch port. Truncation is just for the single
output action, so that later actions in the OpenFlow pipeline work with the complete
packet. The truncation feature is meant for use in monitoring applications, e.g. for
mirroring packets to a collector.
When an output action specifies the number of a port that does not currently exist (and is
not in the range for standard ports), the OpenFlow specification allows but does not
require OVS to reject the action. All versions of Open vSwitch treat such an action as a
no-op. If a port with the number is created later, then the action will be honored at
that point. (OpenFlow requires OVS to reject output to a port number that will never be
valid, with OFPBAC_BAD_OUT_PORT, but this situation does not arise when OVS is a software
switch, since the user can add or renumber ports at any time.)
A controller can suppress output to a port by setting its OFPPC_NO_FORWARD flag using an
OpenFlow OFPT_MOD_PORT request (ovs-ofctl mod-port provides a command-line interface to
set this flag). When output is disabled, output actions (and other actions that output to
the port) are allowed but have no effect.
Open vSwitch allows output to a port that does not exist, although OpenFlow allows
switches to reject such actions.
Conformance
All versions of OpenFlow and Open vSwitch support output to a literal port. Output
to a register is an OpenFlow extension introduced in Open vSwitch 1.3. Output with
truncation is an OpenFlow extension introduced in Open vSwitch 2.6.
Output to the Input Port
OpenFlow requires a switch to ignore attempts to send a packet out its ingress port in the
most straightforward way. For example, output:234 has no effect if the packet has ingress
port 234. The rationale is that dropping these packets makes it harder to loop the
network. Sometimes this behavior can even be convenient, e.g. it is often the desired
behavior in a flow that forwards a packet to several ports (floods the packet).
Sometimes one really needs to send a packet out its ingress port (hairpin). In this case,
use in_port to explicitly output the packet to its input port, e.g.:
$ ovs-ofctl add-flow br0 in_port=2,actions=in_port
This also works in some circumstances where the flow doesn’t match on the input port. For
example, if you know that your switch has five ports numbered 2 through 6, then the
following will send every received packet out every port, even its ingress port:
$ ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
or, equivalently:
$ ovs-ofctl add-flow br0 actions=all,in_port
Sometimes, in complicated flow tables with multiple levels of resubmit actions, a flow
needs to output to a particular port that may or may not be the ingress port. It’s
difficult to take advantage of output to in_port in this situation. To help, Open vSwitch
provides, as an OpenFlow extension, the ability to modify the in_port field. Whatever
value is currently in the in_port field is both the port to which output will be dropped
and the destination for in_port. This means that the following adds flows that reliably
output to port 2 or to ports 2 through 6, respectively:
$ ovs-ofctl add-flow br0 "in_port=2,actions=load:0->in_port,2"
$ ovs-ofctl add-flow br0 "actions=load:0->in_port,2,3,4,5,6"
If in_port is important for matching or other reasons, one may save and restore it on the
stack:
$ ovs-ofctl add-flow br0 \
actions="push:in_port,load:0->in_port,2,3,4,5,6,pop:in_port"
The OVS Normal Pipeline
This section documents how Open vSwitch implements output to the normal port. The
OpenFlow specification places no requirements on how this port works, so all of this
documentation is specific to Open vSwitch.
Open vSwitch uses the Open_vSwitch database, detailed in ovs-vswitchd.conf.db(5), to
determine the details of the normal pipeline.
The normal pipeline executes the following ingress stages for each packet. Each stage
either accepts the packet, in which case the packet goes on to the next stage, or drops
the packet, which terminates the pipeline. The result of the ingress stages is a set of
output ports, which is the empty set if some ingress stage drops the packet:
1. Input port lookup: Looks up the OpenFlow in_port field’s value to the corresponding
Port and Interface record in the database.
The in_port is normally the OpenFlow port that the packet was received on. If
set_field or another actions changes the in_port, the updated value is honored.
Accept the packet if the lookup succeeds, which it normally will. If the lookup
fails, for example because in_port was changed to an unknown value, drop the packet.
2. Drop malformed packet: If the packet is malformed enough that it contains only part of
an 802.1Q header, then drop the packet with an error.
3. Drop packets sent to a port reserved for mirroring: If the packet was received on a
port that is configured as the output port for a mirror (that is, it is the
output_port in some Mirror record), then drop the packet.
4. VLAN input processing: This stage determines what VLAN the packet is in. It also
verifies that this VLAN is valid for the port; if not, drop the packet. How the VLAN
is determined and which ones are valid vary based on the vlan-mode in the input port’s
Port record:
trunk The packet is in the VLAN specified in its 802.1Q header, or in VLAN 0 if
there is no 802.1Q header. The trunks column in the Port record lists the
valid VLANs; if it is empty, all VLANs are valid.
access The packet is in the VLAN specified in the tag column of its Port record.
The packet must not have an 802.1Q header with a nonzero VLAN ID; if it
does, drop the packet.
native-tagged / native-untagged
Same as trunk except that the VLAN of a packet without an 802.1Q header is
not necessarily zero; instead, it is taken from the tag column.
dot1q-tunnel
The packet is in the VLAN specified in the tag column of its Port record,
which is a QinQ service VLAN with the Ethertype specified by the Port’s
other_config:qinq-ethtype. If the packet has an 802.1Q header, then it
specifies the customer VLAN. The cvlans column specifies the valid customer
VLANs; if it is empty, all customer VLANs are valid.
5. Drop reserved multicast addresses: If the packet is addressed to a reserved Ethernet
multicast address and the Bridge record does not have other_config:forward-bpdu set to
true, drop the packet.
6. LACP bond admissibility: This step applies only if the input port is a member of a
bond (a Port with more than one Interface) and that bond is configured to use LACP.
Otherwise, skip to the next step.
The behavior here depends on the state of LACP negotiation:
• If LACP has been negotiated with the peer, accept the packet if the bond member
is enabled (i.e. carrier is up and it hasn’t been administratively disabled).
Otherwise, drop the packet.
• If LACP negotiation is incomplete, then drop the packet. There is one exception:
if fallback to active-backup mode is enabled, continue with the next step,
pretending that the active-backup balancing mode is in use.
7. Non-LACP bond admissibility: This step applies if the input port is a member of a bond
without LACP configured, or if a LACP bond falls back to active-backup as described in
the previous step. If neither of these applies, skip to the next step.
If the packet is an Ethernet multicast or broadcast, and not received on the bond’s
active member, drop the packet.
The remaining behavior depends on the bond’s balancing mode:
L4 (aka TCP balancing)
Drop the packet (this balancing mode is only supported with LACP).
Active-backup
Accept the packet only if it was received on the active member.
SLB (Source Load Balancing)
Drop the packet if the bridge has not learned the packet’s source address
(in its VLAN) on the port that received it. Otherwise, accept the packet
unless it is a gratuitous ARP. Otherwise, accept the packet if the MAC
entry we found is ARP-locked. Otherwise, drop the packet. (See the SLB
Bonding section in the OVS bonding document for more information and a
rationale.)
8. Learn source MAC: If the source Ethernet address is not a multicast address, then
insert a mapping from packet’s source Ethernet address and VLAN to the input port in
the bridge’s MAC learning table. (This is skipped if the packet’s VLAN is listed in
the switch’s Bridge record in the flood_vlans column, since there is no use for MAC
learning when all packets are flooded.)
When learning happens on a non-bond port, if the packet is a gratuitous ARP, the entry
is marked as ARP-locked. The lock expires after 5 seconds. (See the SLB Bonding
section in the OVS bonding document for more information and a rationale.)
9. IP multicast path: If multicast snooping is enabled on the bridge, and the packet is
an Ethernet multicast but not an Ethernet broadcast, and the packet is an IP packet,
then the packet takes a special processing path. This path is not yet documented
here.
10. Output port set: Search the MAC learning table for the port corresponding to the
packet’s Ethernet destination and VLAN. If the search finds an entry, the output port
set is just the learned port. Otherwise (including the case where the packet is an
Ethernet multicast or in flood_vlans), the output port set is all of the ports in the
bridge that belong to the packet’s VLAN, except for any ports that were disabled for
flooding via OpenFlow or that are configured in a Mirror record as a mirror
destination port.
The following egress stages execute once for each element in the set of output ports.
They execute (conceptually) in parallel, so that a decision or action taken for a given
output port has no effect on those for another one:
1. Drop loopback: If the output port is the same as the input port, drop the packet.
2. VLAN output processing: This stage adjusts the packet to represent the VLAN in the
correct way for the output port. Its behavior varies based on the vlan-mode in the
output port’s Port record:
trunk / native-tagged / native-untagged
If the packet is in VLAN 0 (for native-untagged, if the packet is in the
native VLAN) drops any 802.1Q header. Otherwise, ensures that there is an
802.1Q header designating the VLAN.
access Remove any 802.1Q header that was present.
dot1q-tunnel
Ensures that the packet has an outer 802.1Q header with the QinQ Ethertype
and the specified configured tag, and an inner 802.1Q header with the
packet’s VLAN.
3. VLAN priority tag processing: If VLAN output processing discarded the 802.1Q headers,
but priority tags are enabled with other_config:priority-tags in the output port’s Port
record, then a priority-only tag is added (perhaps only if the priority would be
nonzero, depending on the configuration).
4. Bond member choice: If the output port is a bond, the code chooses a particular member.
This step is skipped for non-bonded ports.
If the bond is configured to use LACP, but LACP negotiation is incomplete, then
normally the packet is dropped. The exception is that if fallback to active-backup
mode is enabled, the egress pipeline continues choosing a bond member as if
active-backup mode was in use.
For active-backup mode, the output member is the active member. Other modes hash
appropriate header fields and use the hash value to choose one of the enabled members.
5. Output: The pipeline sends the packet to the output port.
The controller action
Syntax:
controller
controller:max_len
controller(key[=value], ...)
Sends the packet and its metadata to an OpenFlow controller or controllers encapsulated in
an OpenFlow packet-in message. The supported options are:
max_len=max_len
Limit to max_len the number of bytes of the packet to send in the packet-in. A
max_len of 0 prevents any of the packet from being sent (thus, only metadata is
included). By default, the entire packet is sent, equivalent to a max_len of
65535. This option has no effect in Open vSwith 2.7 and later: the entire
packet will always be sent.
reason=reason
Specify reason as the reason for sending the message in the packet-in. The
supported reasons are no_match, action, invalid_ttl, action_set, group, and
packet_out. The default reason is action.
id=controller_id
Specify controller_id, a 16-bit integer, as the connection ID of the OpenFlow
controller or controllers to which the packet-in message should be sent. The
default is zero. Zero is also the default connection ID for each controller
connection, and a given controller connection will only have a nonzero
connection ID if its controller uses the NXT_SET_CONTROLLER_ID Open vSwitch
extension to OpenFlow.
userdata=hh...
Supplies the bytes represented as hex digits hh as additional data to the
controller in the packet-in message. Pairs of hex digits may be separated by
periods for readability.
pause Causes the switch to freeze the packet’s trip through Open vSwitch flow tables
and serializes that state into the packet-in message as a continuation, an
additional property in the NXT_PACKET_IN2 message. The controller can later
send the continuation back to the switch in an NXT_RESUME message, which will
restart the packet’s traversal from the point where it was interrupted. This
permits an OpenFlow controller to interpose on a packet midway through
processing in Open vSwitch.
Conformance
All versions of OpenFlow and Open vSwitch support controller action and its max_len
option. The userdata and pause options require the Open vSwitch NXAST_CONTROLLER2
extension action added in Open vSwitch 2.6. In the absence of these options, the
reason (other than reason=action) and controller_id (option than controller_id=0)
options require the Open vSwitch NXAST_CONTROLLER extension action added in Open
vSwitch 1.6.
Open vSwitch 2.7 and later is configured to not buffer packets for the packet-in
event. As a result, the full packet is always sent to controllers. This means
that the max_len option has no effect on the controller action, and all values
(even 0) are equivalent to the default value of 65535.
The enqueue action
Syntax:
enqueue(port,queue)
enqueue:port:queue
Enqueues the packet on the specified queue within port port.
port must be an OpenFlow port number or name as described under Port Specifications above.
port may be in_port or local but the other standard OpenFlow ports are not allowed.
queue must be a number between 0 and 4294967294 (0xfffffffe), inclusive. The number of
actually supported queues depends on the switch. Some OpenFlow implementations do not
support queuing at all. In Open vSwitch, the supported queues vary depending on the
operating system, datapath, and hardware in use. Use the QoS and Queue tables in the Open
vSwitch database to configure queuing on individual OpenFlow ports (see
ovs-vswitchd.conf.db(5) for more information).
Conformance
Only OpenFlow 1.0 supports enqueue. OpenFlow 1.1 added the set_queue action to use
in its place along with output.
Open vSwitch translates enqueue to a sequence of three actions in OpenFlow 1.1 or
later: set_queue:queue,output:port,pop_queue. This is equivalent in behavior as
long as the flow table does not otherwise use set_queue, but it relies on the
pop_queue Open vSwitch extension action.
The bundle and bundle_load actions
Syntax:
bundle(fields,basis,algorithm,ofport,members:port...)
bundle_load(fields,basis,algorithm,ofport,dst,members:port...)
These actions choose a port (a member) from a comma-separated OpenFlow port list. After
selecting the port, bundle outputs to it, whereas bundle_load writes its port number to
dst, which must be a 16-bit or wider field or subfield in the syntax described under Field
Specifications above.
These actions hash a set of fields using basis as a universal hash parameter, then apply
the bundle link selection algorithm to choose a port.
fields must be one of the following. For the options with symmetric in the name,
reversing source and destination addresses yields the same hash:
eth_src
Ethernet source address.
nw_src IPv4 or IPv6 source address.
nw_dst IPv4 or IPv6 destination address.
symmetric_l4
Ethernet source and destination, Ethernet type, VLAN ID or IDs (if any), IPv4 or
IPv6 source and destination, IP protocol, TCP or SCTP (but not UDP) source and
destination.
symmetric_l3l4
IPv4 or IPv6 source and destination, IP protocol, TCP or SCTP (but not UDP)
source and destination.
symmetric_l3l4+udp
Like symmetric_l3l4 but include UDP ports.
algorithm must be one of the following:
active_backup
Chooses the first live port listed in members.
hrw (Highest Random Weight)
Computes the following, considering only the live ports in members:
for i in [1, n_members]:
weights[i] = hash(flow, i)
member = { i such that weights[i] >= weights[j] for all j != i }
This algorithm is specified by RFC 2992.
The algorithms take port liveness into account when selecting members. The definition of
whether a port is live is subject to change. It currently takes into account carrier
status and link monitoring protocols such as BFD and CFM. If none of the members is live,
bundle does not output the packet and bundle_load stores OFPP_NONE (65535) in the output
field.
Example: bundle(eth_src,0,hrw,ofport,members:4,8) uses an Ethernet source hash with basis
0, to select between OpenFlow ports 4 and 8 using the Highest Random Weight algorithm.
Conformance
Open vSwitch 1.2 introduced the bundle and bundle_load OpenFlow extension actions.
The group action
Syntax:
group:group
Outputs the packet to the OpenFlow group group, which must be a number in the range 0 to
4294967040 (0xffffff00). The group must exist or Open vSwitch will refuse to add the
flow. When a group is deleted, Open vSwitch also deletes all of the flows that output to
it.
Groups contain action sets, whose semantics are described above in the section Action
Sets. The semantics of action sets can be surprising to users who expect action list
semantics, since action sets reorder and sometimes ignore actions.
A group action usually executes the action set or sets in one or more group buckets. Open
vSwitch saves the packet and metadata before it executes each bucket, and then restores it
afterward. Thus, when a group executes more than one bucket, this means that each bucket
executes on the same packet and metadata. Moreover, regardless of the number of buckets
executed, the packet and metadata are the same before and after executing the group.
Sometimes saving and restoring the packet and metadata can be undesirable. In these
situations, workarounds are possible. For example, consider a pipeline design in which a
select group bucket is to communicate to a later stage of processing a value based on
which bucket was selected. An obvious design would be for the bucket to communicate the
value via set_field on a register. This does not work because registers are part of the
metadata that group saves and restores. The following alternative bucket designs do work:
• Recursively invoke the rest of the pipeline with resubmit.
• Use resubmit into a table that uses push to put the value on the stack for the caller
to pop off. This works because group preserves only packet data and metadata, not
the stack.
(This design requires indirection through resubmit because actions sets may not
contain push or pop actions.)
An exit action within a group bucket terminates only execution of that bucket, not other
buckets or the overall pipeline.
Conformance
OpenFlow 1.1 introduced group. Open vSwitch 2.6 and later also supports group as
an extension to OpenFlow 1.0.
ENCAPSULATION AND DECAPSULATION ACTIONS
The strip_vlan and pop actions
Syntax:
strip_vlan
pop_vlan
Removes the outermost VLAN tag, if any, from the packet.
The two names for this action are synonyms with no semantic difference. The OpenFlow 1.0
specification uses the name strip_vlan and later versions use pop_vlan, but OVS accepts
either name regardless of version.
In OpenFlow 1.1 and later, consistency rules allow strip_vlan only in a flow that matches
only packets with a VLAN tag (or following an action that pushes a VLAN tag, such as
push_vlan). See Inconsistencies, above, for more information.
Conformance
All versions of OpenFlow and Open vSwitch support this action.
The push_vlan action
Syntax:
push_vlan:ethertype
Pushes a new outermost VLAN onto the packet. Uses TPID ethertype, which must be 0x8100
for an 802.1Q C-tag or 0x88a8 for a 802.1ad S-tag.
Conformance
OpenFlow 1.1 and later supports this action. Open vSwitch 2.8 added support for
multiple VLAN tags (with a limit of 2) and 802.1ad S-tags.
The push_mpls action
Syntax:
push_mpls:ethertype
Pushes a new outermost MPLS label stack entry (LSE) onto the packet and changes the
packet’s Ethertype to ethertype, which must be either B0x8847 or 0x8848. If the packet
did not already contain any MPLS labels, initializes the new LSE as:
Label 2, if the packet contains IPv6, 0 otherwise.
TC The low 3 bits of the packet’s DSCP value, or 0 if the packet is not IP.
TTL Copied from the IP TTL, or 64 if the packet is not IP.
If the packet did already contain an MPLS label, initializes the new outermost label as a
copy of the existing outermost label.
OVS currently supports at most 3 MPLS labels.
This action applies only to Ethernet packets.
Conformance
Open vSwitch 1.11 introduced support for MPLS. OpenFlow 1.1 and later support
push_mpls. Open vSwitch implements push_mpls as an extension to OpenFlow 1.0.
The pop_mpls action
Syntax:
pop_mpls:ethertype
Strips the outermost MPLS label stack entry and changes the packet’s Ethertype to
ethertype. This action applies only to Ethernet packets with at least one MPLS label. If
there is more than one MPLS label, then ethertype should be an MPLS Ethertype (B0x8847 or
0x8848).
Conformance
Open vSwitch 1.11 introduced support for MPLS. OpenFlow 1.1 and later support
pop_mpls. Open vSwitch implements pop_mpls as an extension to OpenFlow 1.0.
The encap action
Syntax:
encap(nsh([md_type=md_type], [tlv(class,type,value)]...))
encap(ethernet)
encap(mpls)
encap(mpls_mc)
The encap action encapsulates a packet with a specified header. It has variants for
different kinds of encapsulation.
The encap(nsh(...)) variant encapsulates an Ethernet frame with NSH. The md_type may be 1
or 2 for metadata type 1 or 2, defaulting to 1. For metadata type 2, TLVs may be
specified with class as a 16-bit hexadecimal integer beginning with 0x, type as an 8-bit
decimal integer, and value a sequence of pairs of hex digits beginning with 0x. For
example:
encap(nsh(md_type=1))
Encapsulates the packet with an NSH header with metadata type 1.
encap(nsh(md_type=2,tlv(0x1000,10,0x12345678)))
Encapsulates the packet with an NSH header, NSH metadata type 2, and an NSH TLV
with class 0x1000, type 10, and the 4-byte value 0x12345678.
The encap(ethernet) variant encapsulate a bare L3 packet in an Ethernet frame. The
Ethernet type is initialized to the L3 packet’s type, e.g. 0x0800 if the L3 packet is
IPv4. The Ethernet source and destination are initially zeroed.
The encap(mpls) variant adds a MPLS header at the start of the packet. When
encap(ethernet) is applied after this action, the ethertype of ethernet header will be
populated with MPLS unicast ethertype (0x8847).
The encap(mpls_mc) variant adds a MPLS header at the start of the packet. When
encap(ethernet) is applied after this action, the ethertype of ethernet header will be
populated with MPLS multicast ethertype (0x8848).
Conformance
This action is an Open vSwitch extension to OpenFlow 1.3 and later, introduced in
Open vSwitch 2.8.
The MPLS support for this action is added in Open vSwitch 2.17.
The decap action
Syntax:
decap
decap(packet_type(ns=namespace,type=type))
Removes an outermost encapsulation from the packet:
• If the packet is an Ethernet packet, removes the Ethernet header, which changes the
packet into a bare L3 packet. If the packet has VLAN tags, raises an unsupported
packet type error (see Error Handling, above).
• Otherwise, if the packet is an NSH packet, removes the NSH header, revealing the
inner packet. Open vSwitch supports Ethernet, IPv4, IPv6, and NSH inner packet
types. Other types raise unsupported packet type errors.
• Otherwise, if the packet is encapsulated inside a MPLS header, removes the MPLS
header and classifies the inner packet as mentioned in the packet type argument of
the decap. The packet_type field specifies the type of the packet in the format
specified in OpenFlow 1.5 chapter 7.2.3.11 Packet Type Match Field. The inner packet
will be incorrectly classified, if the inner packet is different from mentioned in
the packet_type field.
• Otherwise, raises an unsupported packet type error.
Conformance
This action is an Open vSwitch extension to OpenFlow 1.3 and later, introduced in
Open vSwitch 2.8.
The MPLS support for this action is added in Open vSwitch 2.17.
FIELD MODIFICATION ACTIONS
These actions modify packet data and metadata fields.
The set_field and load actions
Syntax:
set_field:value[/mask]->dst
load:value->dst
These actions loads a literal value into a field or part of a field. The set_field action
takes value in the customary syntax for field dst, e.g. 00:11:22:33:44:55 for an Ethernet
address, and dst as the field’s name. The optional mask allows part of a field to be set.
The load action takes value as an integer value (in decimal or prefixed by 0x for
hexadecimal) and dst as a field or subfield in the syntax described under Field
Specifications above.
The following all set the Ethernet source address to 00:11:22:33:44:55:
• set_field:00:11:22:33:44:55->eth_src
• load:0x001122334455->eth_src
• load:0x001122334455->OXM_OF_ETH_SRC[]
The following all set the multicast bit in the Ethernet destination address:
• set_field:01:00:00:00:00:00/01:00:00:00:00:00->eth_dst
• load:1->eth_dst[40]
Open vSwitch prohibits a set_field or load action whose dst is not guaranteed to be part
of the packet; for example, set_field of nw_dst is only allowed in a flow that matches on
Ethernet type 0x800. In some cases, such as in an action set, Open vSwitch can’t
statically check that dst is part of the packet, and in that case if it is not then Open
vSwitch treats the action as a no-op.
Conformance
Open vSwitch 1.1 introduced NXAST_REG_LOAD as a extension to OpenFlow 1.0 and used
load to express it. Later, OpenFlow 1.2 introduced a standard OFPAT_SET_FIELD
action that was restricted to loading entire fields, so Open vSwitch added the form
set_field with this restriction. OpenFlow 1.5 extended OFPAT_SET_FIELD to the
point that it became a superset of NXAST_REG_LOAD. Open vSwitch translates either
syntax as necessary for the OpenFlow version in use: in OpenFlow 1.0 and 1.1,
NXAST_REG_LOAD; in OpenFlow 1.2, 1.3, and 1.4, NXAST_REG_LOAD for load or for
loading a subfield, OFPAT_SET_FIELD otherwise; and OpenFlow 1.5 and later,
OFPAT_SET_FIELD.
The move action
Syntax:
move:src->dst
Copies the named bits from field or subfield src to field or subfield dst. src and dst
should fields or subfields in the syntax described under Field Specifications above. The
two fields or subfields must have the same width.
Examples:
• move:reg0[0..5]->reg1[26..31] copies the six bits numbered 0 through 5 in register 0
into bits 26 through 31 of register 1.
• move:reg0[0..15]->vlan_tci copies the least significant 16 bits of register 0 into
the VLAN TCI field.
Conformance
In OpenFlow 1.0 through 1.4, move ordinarily uses an Open vSwitch extension to
OpenFlow. In OpenFlow 1.5, move uses the OpenFlow 1.5 standard OFPAT_COPY_FIELD
action. The ONF has also made OFPAT_COPY_FIELD available as an extension to
OpenFlow 1.3. Open vSwitch 2.4 and later understands this extension and uses it if
a controller uses it, but for backward compatibility with older versions of Open
vSwitch, ovs-ofctl does not use it.
The mod_dl_src and mod_dl_dst actions
Syntax:
mod_dl_src:mac
mod_dl_dst:mac
Sets the Ethernet source or destination address, respectively, to mac, which should be
expressed in the form xx:xx:xx:xx:xx:xx.
For L3-only packets, that is, those that lack an Ethernet header, this action has no
effect.
Conformance
OpenFlow 1.0 and 1.1 have specialized actions for these purposes. OpenFlow 1.2 and
later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD
actions for those versions,
The mod_nw_src and mod_nw_dst actions
Syntax:
mod_nw_src:ip
mod_nw_dst:ip
Sets the IPv4 source or destination address, respectively, to ip, which should be
expressed in the form w.x.y.z.
In OpenFlow 1.1 and later, consistency rules allow these actions only in a flow that
matches only packets that contain an IPv4 header (or following an action that adds an IPv4
header, e.g. pop_mpls:0x0800). See Inconsistencies, above, for more information.
Conformance
OpenFlow 1.0 and 1.1 have specialized actions for these purposes. OpenFlow 1.2 and
later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD
actions for those versions,
The mod_nw_tos and mod_nw_ecn actions
Syntax:
mod_nw_tos:tos
mod_nw_ecn:ecn
The mod_nw_tos action sets the DSCP bits in the IPv4 ToS/DSCP or IPv6 traffic class field
to tos, which must be a multiple of 4 between 0 and 255. This action does not modify the
two least significant bits of the ToS field (the ECN bits).
The mod_nw_ecn action sets the ECN bits in the IPv4 ToS or IPv6 traffic class field to
ecn, which must be a value between 0 and 3, inclusive. This action does not modify the
six most significant bits of the field (the DSCP bits).
In OpenFlow 1.1 and later, consistency rules allow these actions only in a flow that
matches only packets that contain an IPv4 or IPv6 header (or following an action that adds
such a header). See Inconsistencies, above, for more information.
Conformance
OpenFlow 1.0 has a mod_nw_tos action but not mod_nw_ecn. Open vSwitch implements
the latter in OpenFlow 1.0 as an extension using NXAST_REG_LOAD. OpenFlow 1.1 has
specialized actions for these purposes. OpenFlow 1.2 and later do not, so Open
vSwitch translates them to appropriate OFPAT_SET_FIELD actions for those versions.
The mod_tp_src and mod_tp_dst actions
Syntax:
mod_tp_src:port
mod_tp_dst:port
Sets the TCP or UDP or SCTP source or destination port, respectively, to port. Both IPv4
and IPv6 are supported.
In OpenFlow 1.1 and later, consistency rules allow these actions only in a flow that
matches only packets that contain a TCP or UDP or SCTP header. See Inconsistencies,
above, for more information.
Conformance
OpenFlow 1.0 and 1.1 have specialized actions for these purposes. OpenFlow 1.2 and
later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD
actions for those versions,
The dec_ttl action
Syntax:
dec_ttl
dec_ttl(id1[,id2[, ...]])
Decrement TTL of IPv4 packet or hop limit of IPv6 packet. If the TTL or hop limit is
initially 0 or 1, no decrement occurs, as packets reaching TTL zero must be rejected.
Instead, Open vSwitch sends a packet-in message with reason code OFPR_INVALID_TTL to each
connected controller that has enabled receiving such messages, and stops processing the
current set of actions. (However, if the current set of actions was reached through
resubmit, the remaining actions in outer levels resume processing.)
As an Open vSwitch extension to OpenFlow, this action supports the ability to specify a
list of controller IDs. Open vSwitch will only send the message to controllers with the
given ID or IDs. Specifying no list is equivalent to specifying a single controller ID of
zero.
In OpenFlow 1.1 and later, consistency rules allow these actions only in a flow that
matches only packets that contain an IPv4 or IPv6 header. See Inconsistencies, above, for
more information.
Conformance
All versions of OpenFlow and Open vSwitch support this action.
The set_mpls_label, set_mpls_tc, and set_mpls_ttl actions
Syntax:
set_mpls_label:label
set_mpls_tc:tc
set_mpls_ttl:ttl
The set_mpls_label action sets the label of the packet’s outer MPLS label stack entry.
label should be a 20-bit value that is decimal by default; use a 0x prefix to specify the
value in hexadecimal.
The set_mpls_tc action sets the traffic class of the packet’s outer MPLS label stack
entry. tc should be in the range 0 to 7, inclusive.
The set_mpls_ttl action sets the TTL of the packet’s outer MPLS label stack entry. ttl
should be in the range 0 to 255 inclusive. In OpenFlow 1.1 and later, consistency rules
allow these actions only in a flow that matches only packets that contain an MPLS label
(or following an action that adds an MPLS label, e.g. push_mpls:0x8847). See
Inconsistencies, above, for more information.
Conformance
OpenFlow 1.0 does not support MPLS, but Open vSwitch implements these actions as
extensions. OpenFlow 1.1 has specialized actions for these purposes. OpenFlow 1.2
and later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD
actions for those versions,
The dec_mpls_ttl and dec_nsh_ttl actions
Syntax:
dec_mpls_ttl
dec_nsh_ttl
These actions decrement the TTL of the packet’s outer MPLS label stack entry or its NSH
header, respectively. If the TTL is initially 0 or 1, no decrement occurs. Instead, Open
vSwitch sends a packet-in message with reason code BOFPR_INVALID_TTL to OpenFlow
controllers with ID 0, if it has enabled receiving them. Processing the current set of
actions then stops. (However, if the current set of actions was reached through resubmit,
remaining actions in outer levels resume processing.)
In OpenFlow 1.1 and later, consistency rules allow this actions only in a flow that
matches only packets that contain an MPLS label or an NSH header, respectively. See
Inconsistencies, above, for more information.
Conformance
Open vSwitch 1.11 introduced support for MPLS. OpenFlow 1.1 and later support
dec_mpls_ttl. Open vSwitch implements dec_mpls_ttl as an extension to OpenFlow
1.0.
Open vSwitch 2.8 introduced support for NSH, although the NSH draft changed after
release so that only Open vSwitch 2.9 and later conform to the final protocol
specification. The dec_nsh_ttl action and NSH support in general is an Open
vSwitch extension not supported by any version of OpenFlow.
The check_pkt_larger action
Syntax:
check_pkt_larger(pkt_len)->dst
Checks if the packet is larger than the specified length in pkt_len. If so, stores 1 in
dst, which should be a 1-bit field; if not, stores 0.
The packet length to check against the argument pkt_len includes the L2 header and L2
payload of the packet, but not the VLAN tag (if present).
Examples:
• check_pkt_larger(1500)->reg0[0]
• check_pkt_larger(8000)->reg9[10]
This action was added in Open vSwitch 2.12.
The delete_field action
Syntax:
delete_field:field
The delete_field action deletes a field in the syntax described under Field Specifications
above. Currently, only the tun_metadata fields are supported.
This action was added in Open vSwitch 2.14.
METADATA ACTIONS
The set_tunnel action
Syntax:
set_tunnel:id
set_tunnel64:id
Many kinds of tunnels support a tunnel ID, e.g. VXLAN and Geneve have a 24-bit VNI, and
GRE has an optional 32-bit key. This action sets the value used for tunnel ID in such
tunneled packets, although whether it is used for a particular tunnel depends on the
tunnel’s configuration. See the tunnel ID documentation in ovs-fields(7) for more
information.
Conformance
These actions are OpenFlow extensions. set_tunnel was introduced in Open vSwitch
1.0. set_tunnel64, which is needed if id is wider than 32 bits, was added in Open
vSwitch 1.1. Both actions always set the entire tunnel ID field. Open vSwitch
supports these actions in all versions of OpenFlow, but in OpenFlow 1.2 and later
it translates them to an appropriate standardized OFPAT_SET_FIELD action.
The set_queue and pop_queue actions
Syntax:
set_queue:queue
pop_queue
The set_queue action sets the queue ID to be used for subsequent output actions to queue,
which must be a 32-bit integer. The range of meaningful values of queue, 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. For more information, see the documentation for the output queue field in
ovs-fields(7).
The pop_queue restores the output queue to the default that was set when the packet
entered the switch (generally 0).
Four billion queues ought to be enough for anyone: ‐
https://mailman.stanford.edu/pipermail/openflow-spec/2009-August/000394.html
Conformance
OpenFlow 1.1 introduced the set_queue action. Open vSwitch also supports it as an
extension in OpenFlow 1.0.
The pop_queue action is an Open vSwitch extension.
FIREWALLING ACTIONS
Open vSwitch is often used to implement a firewall. The preferred way to implement a
firewall is connection tracking, that is, to keep track of the connection state of
individual TCP sessions. The ct action described in this section, added in Open vSwitch
2.5, implements connection tracking. For new deployments, it is the recommended way to
implement firewalling with Open vSwitch.
Before ct was added, Open vSwitch did not have built-in support for connection tracking.
Instead, Open vSwitch supported the learn action, which allows a received packet to add a
flow to an OpenFlow flow table. This could be used to implement a primitive form of
connection tracking: packets passing through the firewall in one direction could create
flows that allowed response packets back through the firewall in the other direction. The
additional fin_timeout action allowed the learned flows to expire quickly after TCP
session termination.
The ct action
Syntax:
ct([argument]...)
ct(commit[,argument]...)
The action has two modes of operation, distinguished by whether commit is present. The
following arguments may be present in either mode:
zone=value
A zone is a 16-bit id that isolates connections into separate domains, allowing
overlapping network addresses in different zones. If a zone is not provided,
then the default is 0. The value may be specified either as a 16-bit integer
literal or a field or subfield in the syntax described under Field
Specifications above.
Without commit, this action sends the packet through the connection tracker. The
connection tracker keeps track of the state of TCP connections for packets passed through
it. For each packet through a connection, it checks that it satisfies TCP invariants and
signals the connection state to later actions using the ct_state metadata field, which is
documented in ovs-fields(7).
In this form, ct forks the OpenFlow pipeline:
• In one fork, ct passes the packet to the connection tracker. Afterward, it reinjects
the packet into the OpenFlow pipeline with the connection tracking fields
initialized. The ct_state field is initialized with connection state and ct_zone to
the connection tracking zone specified on the zone argument. If the connection is
one that is already tracked, ct_mark and ct_label to its existing mark and label,
respectively; otherwise they are zeroed. In addition, ct_nw_proto, ct_nw_src,
ct_nw_dst, ct_ipv6_src, ct_ipv6_dst, ct_tp_src, and ct_tp_dst are initialized
appropriately for the original direction connection. See the resubmit action for a
way to search the flow table with the connection tracking original direction fields
swapped with the packet 5-tuple fields. See ovs-fields(7) for details on the
connection tracking fields.
• In the other fork, the original instance of the packet continues independent
processing following the ct action. The ct_state field and other connection tracking
metadata are cleared.
Without commit, the ct action accepts the following arguments:
table=table
Sets the OpenFlow table where the packet is reinjected. The table must be a
number between 0 and 254 inclusive, or a table’s name. If table is not
specified, then the packet is not reinjected.
nat
nat(type=addrs[:ports][,flag]...)
Specify address and port translation for the connection being tracked. The
type must be src, for source address/port translation (SNAT), or dst, for
destination address/port translation (DNAT). Setting up address translation for
a new connection takes effect only if the connection is later committed with
ct(commit ...).
The src and dst options take the following arguments:
addrs The IP address addr or range addr1-addr2 from which the translated
address should be selected. If only one address is given, then that
address will always be selected, otherwise the address selection can
be informed by the optional persistent flag as described below.
Either IPv4 or IPv6 addresses can be provided, but both addresses
must be of the same type, and the datapath behavior is undefined in
case of providing IPv4 address range for an IPv6 packet, or IPv6
address range for an IPv4 packet. IPv6 addresses must be bracketed
with [ and ] if a port range is also given.
ports The L4 port or range port1-port2 from which the translated port
should be selected. When a port range is specified, fallback to
ephemeral ports does not happen, else, it will. The port number
selection can be informed by the optional random and hash flags
described below.
The optional flags are:
random The selection of the port from the given range should be done using a
fresh random number. This flag is mutually exclusive with hash.
hash The selection of the port from the given range should be done using a
datapath specific hash of the packet’s IP addresses and the other,
non-mapped port number. This flag is mutually exclusive with random.
persistent
The selection of the IP address from the given range should be done
so that the same mapping can be provided after the system restarts.
If alg is specified for the committing ct action that also includes nat with a
src or dst attribute, then the datapath tries to set up the helper to be
NAT-aware. This functionality is datapath specific and may not be supported by
all datapaths.
A bare nat argument with no options will only translate the packet being
processed in the way the connection has been set up with an earlier, committed
ct action. A nat action with src or dst, when applied to a packet belonging to
an established (rather than new) connection, will behave the same as a bare nat.
For SNAT, there is a special case when the src IP address is configured as all
0’s, i.e., nat(src=0.0.0.0). In this case, when a source port collision is
detected during the commit, the source port will be translated to an ephemeral
port. If there is no collision, no SNAT is performed.
Open vSwitch 2.6 introduced nat. Linux 4.6 was the earliest upstream kernel
that implemented ct support for nat.
With commit, the connection tracker commits the connection to the connection tracking
module. The commit flag should only be used from the pipeline within the first fork of ct
without commit. Information about the connection is stored beyond the lifetime of the
packet in the pipeline. Some ct_state flags are only available for committed connections.
The following options are available only with commit:
force A committed connection always has the directionality of the packet that caused
the connection to be committed in the first place. This is the original
direction of the connection, and the opposite direction is the reply direction.
If a connection is already committed, but it is in the wrong direction, force
effectively terminates the existing connection and starts a new one in the
current direction. This flag has no effect if the original direction of the
connection is already the same as that of the current packet.
exec(action...)
Perform each action within the context of connection tracking. Only actions
which modify the ct_mark or ct_label fields are accepted within exec action, and
these fields may only be modified with this option. For example:
set_field:value[/mask]->ct_mark
Store a 32-bit metadata value with the connection. Subsequent lookups
for packets in this connection will populate ct_mark when the packet is
sent to the connection tracker with the table specified.
set_field:value[/mask]->ct_label
Store a 128-bit metadata value with the connection. Subsequent lookups
for packets in this connection will populate ct_label when the packet is
sent to the connection tracker with the table specified.
alg=alg
Specify application layer gateway alg to track specific connection types. If
subsequent related connections are sent through the ct action, then the rel flag
in the ct_state field will be set. Supported types include:
ftp Look for negotiation of FTP data connections. Specify this option for
FTP control connections to detect related data connections and populate
the rel flag for the data connections.
tftp Look for negotiation of TFTP data connections. Specify this option for
TFTP control connections to detect related data connections and populate
the rel flag for the data connections.
Related connections inherit ct_mark from that stored with the original
connection (i.e. the connection created by ct(alg=...).
With the Linux datapath, global sysctl options affect ct behavior. In particular, if
net.netfilter.nf_conntrack_helper is enabled, which it is by default until Linux 4.7, then
application layer gateway helpers may be executed even if alg is not specified. For
security reasons, the netfilter team recommends users disable this option. For further
details, please see http://www.netfilter.org/news.html#2012-04-03 .
The ct action may be used as a primitive to construct stateful firewalls by selectively
committing some traffic, then matching ct_state to allow established connections while
denying new connections. The following flows provide an example of how to implement a
simple firewall that allows new connections from port 1 to port 2, and only allows
established connections to send traffic from port 2 to port 1:
table=0,priority=1,action=drop
table=0,priority=10,arp,action=normal
table=0,priority=100,ip,ct_state=-trk,action=ct(table=1)
table=1,in_port=1,ip,ct_state=+trk+new,action=ct(commit),2
table=1,in_port=1,ip,ct_state=+trk+est,action=2
table=1,in_port=2,ip,ct_state=+trk+new,action=drop
table=1,in_port=2,ip,ct_state=+trk+est,action=1
If ct is executed on IPv4 (or IPv6) fragments, then the message is implicitly reassembled
before sending to the connection tracker and refragmented upon output, to the original
maximum received fragment size. Reassembly occurs within the context of the zone, meaning
that IP fragments in different zones are not assembled together. Pipeline processing for
the initial fragments is halted. When the final fragment is received, the message is
assembled and pipeline processing continues for that flow. Packet ordering is not
guaranteed by IP protocols, so it is not possible to determine which IP fragment will
cause message reassembly (and therefore continue pipeline processing). As such, it is
strongly recommended that multiple flows should not execute ct to reassemble fragments
from the same IP message.
Conformance
The ct action was introduced in Open vSwitch 2.5. Some of its features were
introduced later, noted individually above.
The ct_clear action
Syntax:
ct_clear
Clears connection tracking state from the flow, zeroing ct_state, ct_zone, ct_mark, and
ct_label.
This action was introduced in Open vSwitch 2.7.
The learn action
Syntax:
learn(argument...)
The learn action adds or modifies a flow in an OpenFlow table, similar to ovs-ofctl
--strict mod-flows. The arguments specify the match fields, actions, and other properties
of the flow to be added or modified.
Match fields for the new flow are specified as follows. At least one match field should
ordinarily be specified:
field=value
Specifies that field, in the new flow, must match the literal value, e.g.
dl_type=0x800. Shorthand match syntax, such as ip in place of dl_type=0x800, is
not supported.
field=src
Specifies that field in the new flow must match src taken from the packet
currently being processed. For example, udp_dst=udp_src, applied to a UDP
packet with source port 53, creates a flow which matches udp_dst=53. field and
src must have the same width.
field Shorthand for the previous form when field and src are the same. For example,
udp_dst, applied to a UDP packet with destination port 53, creates a flow which
matches udp_dst=53.
The field and src arguments above should be fields or subfields in the syntax described
under Field Specifications above.
Match field specifications must honor prerequisites for both the flow with the learn and
the new flow that it creates. Consider the following complete flow, in the syntax
accepted by ovs-ofctl. If the flow’s match on udp were omitted, then the flow would not
satisfy the prerequisites for the learn action’s use of udp_src. If dl_type=0x800 or
nw_proto were omitted from learn, then the new flow would not satisfy the prerequisite for
its match on udp_dst. For more information on prerequisites, please refer to
ovs-fields(7):
udp, actions=learn(dl_type=0x800, nw_proto=17, udp_dst=udp_src)
Actions for the new flow are specified as follows. At least one action should ordinarily
be specified:
load:value->dst
Adds a load action to the new flow that loads the literal value into dst. The
syntax is the same as the load action explained in the Field Modification
Actions section.
load:src->dst
Adds a load action to the new flow that loads src, a field or subfield from the
packet being processed, into dst.
output:field
Adds an output action to the new flow’s actions that outputs to the OpenFlow
port taken from field, which must be a field as described above.
fin_idle_timeout=seconds / fin_hard_timeout=seconds
Adds a fin_timeout action with the specified arguments to the new flow. This
feature was added in Open vSwitch 1.6.
The following additional arguments are optional:
idle_timeout=seconds
hard_timeout=seconds
priority=value
cookie=value
send_flow_rem
These arguments have the same meaning as in the usual flow syntax documented in
ovs-ofctl(8).
table=table
The table in which the new flow should be inserted. Specify a decimal number
between 0 and 254 inclusive or the name of a table. The default, if table is
unspecified, is table 1 (not 0).
delete_learned
When this flag is specified, deleting the flow that contains the learn action
will also delete the flows created by learn. Specifically, when the last learn
action with this flag and particular table and cookie values is removed, the
switch deletes all of the flows in the specified table with the specified
cookie.
This flag was added in Open vSwitch 2.4.
limit=number
If the number of flows in the new flow’s table with the same cookie exceeds
number, the action will not add a new flow. By default, or with limit=0, there
is no limit.
This flag was added in Open vSwitch 2.8.
result_dst=field[bit]
If learn fails (because the number of flows exceeds limit), the action sets
field[bit] to 0, otherwise it will be set to 1. field[bit] must be a single
bit.
This flag was added in Open vSwitch 2.8.
By itself, the learn action can only put two kinds of actions into the flows that it
creates: load and output actions. If learn is used in isolation, these are severe limits.
However, learn is not meant to be used in isolation. It is a primitive meant to be used
together with other Open vSwitch features to accomplish a task. Its existing features are
enough to accomplish most tasks.
Here is an outline of a typical pipeline structure that allows for versatile behavior
using learn:
• Flows in table A contain a learn action, that populates flows in table L, that use a
load action to populate register R with information about what was learned.
• Flows in table B contain two sequential resubmit actions: one to table L and another
one to table B + 1.
• Flows in table B + 1 match on register R and act differently depending on what the
flows in table L loaded into it.
This approach can be used to implement many learn-based features. For example:
• Resubmit to a table selected based on learned information, e.g. see ‐
https://mail.openvswitch.org/pipermail/ovs-discuss/2016-June/021694.html .
• MAC learning in the middle of a pipeline, as described in the Open vSwitch Advanced
Features Tutorial in the OVS documentation.
• TCP state based firewalling, by learning outgoing connections based on SYN packets
and matching them up with incoming packets. (This is usually better implemented
using the ct action.)
• At least some of the features described in T. A. Hoff, Extending Open vSwitch to
Facilitate Creation of Stateful SDN Applications.
Conformance
The learn action is an Open vSwitch extension to OpenFlow added in Open vSwitch
1.3. Some features of learn were added in later versions, as noted individually
above.
The fin_timeout action
Syntax:
fin_timeout(key=value...)
This action changes the idle timeout or hard timeout, or both, of the OpenFlow flow that
contains it, when the flow matches a TCP packet with the FIN or RST flag. When such a
packet is observed, the action reduces the rule’s timeouts to those specified on the
action. If the rule’s existing timeout is already shorter than the one that the action
specifies, then that timeout is unaffected.
The timeouts are specified as key-value pairs:
idle_timeout=seconds
Causes the flow to expire after the given number of seconds of inactivity.
hard_timeout=seconds
Causes the flow to expire after the given number of seconds, regardless of
activity. (seconds specifies time since the flow’s creation, not since the
receipt of the FIN or RST.)
This action is normally added to a learned flow by the learn action. It is unlikely to be
useful otherwise.
Conformance
This Open vSwitch extension action was added in Open vSwitch 1.6.
PROGRAMMING AND CONTROL FLOW ACTIONS
The resubmit action
Syntax:
resubmit:port
resubmit([port],[table][,ct])``
Searches an OpenFlow flow table for a matching flow and executes the actions found, if
any, before continuing to the following action in the current flow entry. Arguments can
customize the search:
• If port is given as an OpenFlow port number or name, then it specifies a value to use
for the input port metadata field as part of the search, in place of the input port
currently in the flow. Specifying in_port as port is equivalent to omitting it.
• If table is given as an integer between 0 and 254 or a table name, it specifies the
OpenFlow table to search. If it is not specified, the table from the current flow is
used.
• If ct is specified, then the search is done with packet 5-tuple fields swapped with
the corresponding conntrack original direction tuple fields. See the documentation
for ct above, for more information about connection tracking, or ovs-fields(7) for
details about the connection tracking fields.
This flag requires a valid connection tracking state as a match prerequisite in the
flow where this action is placed. Examples of valid connection tracking state
matches include ct_state=+new, ct_state=+est, ct_state=+rel, and ct_state=+trk-inv.
The changes, if any, to the input port and connection tracking fields are just for
searching the flow table. The changes are not visible to actions or to later flow table
lookups.
The most common use of resubmit is to visit another flow table without port or ct, like
this: resubmit(,table).
Recursive resubmit actions are permitted.
Conformance
The resubmit action is an Open vSwitch extension. However, the goto_table
instruction in OpenFlow 1.1 and later can be viewed as a kind of restricted
resubmit.
Open vSwitch 1.3 added table. Open vSwitch 2.7 added ct.
Open vSwitch imposes a limit on resubmit recursion that varies among version:
• Open vSwitch 1.0.1 and earlier did not support recursion.
• Open vSwitch 1.0.2 and 1.0.3 limited recursion to 8 levels.
• Open vSwitch 1.1 and 1.2 limited recursion to 16 levels.
• Open vSwitch 1.2 through 1.8 limited recursion to 32 levels.
• Open vSwitch 1.9 through 2.0 limited recursion to 64 levels.
• Open vSwitch 2.1 through 2.5 limited recursion to 64 levels and impose a total
limit of 4,096 resubmits per flow translation (earlier versions did not impose
any total limit).
• Open vSwitch 2.6 and later imposes the same limits as 2.5, with one exception:
resubmit from table x to any table y > x does not count against the recursion
depth limit.
The clone action
Syntax:
clone(action...)
Executes each nested action, saving much of the packet and pipeline state beforehand and
then restoring it afterward. The state that is saved and restored includes all flow data
and metadata (including, for example, in_port and ct_state), the stack accessed by push
and pop actions, and the OpenFlow action set.
This action was added in Open vSwitch 2.7.
The push and pop actions
Syntax:
push:src
pop:dst
The push action pushes src on a general-purpose stack. The pop action pops an entry off
the stack into dst. src and dst should be fields or subfields in the syntax described
under Field Specifications above.
Controllers can use the stack for saving and restoring data or metadata around resubmit
actions, for swapping or rearranging data and metadata, or for other purposes. Any data
or metadata field, or part of one, may be pushed, and any modifiable field or subfield may
be popped.
The number of bits pushed in a stack entry do not have to match the number of bits later
popped from that entry. If more bits are popped from an entry than were pushed, then the
entry is conceptually left-padded with 0-bits as needed. If fewer bits are popped than
pushed, then bits are conceptually trimmed from the left side of the entry.
The stack’s size is limited. The limit is intended to be high enough that normal use will
not pose problems. Stack overflow or underflow is an error that stops action execution
(see Stack too deep under Error Handling, above).
Examples:
• push:reg2[0..5] or push:NXM_NX_REG2[0..5] pushes on the stack the 6 bits in register
2 bits 0 through 5.
• pop:reg2[0..5] or pop:NXM_NX_REG2[0..5] pops the value from top of the stack and copy
bits 0 through 5 of that value into bits 0 through 5 of register 2.
Conformance
Open vSwitch 1.2 introduced push and pop as OpenFlow extension actions.
The exit action
Syntax:
exit
This action causes Open vSwitch to immediately halt execution of further actions. Actions
which have already been executed are unaffected. Any further actions, including those
which may be in other tables, or different levels of the resubmit call stack, are ignored.
However, an exit action within a group bucket terminates only execution of that bucket,
not other buckets or the overall pipeline. Actions in the action set are still executed
(specify clear_actions before exit to discard them).
The multipath action
Syntax:
multipath(fields,basis,algorithm,n_links,arg,dst)
Hashes fields using basis as a universal hash parameter, then the applies multipath link
selection algorithm (with parameter arg) to choose one of n_links output links numbered 0
through n_links minus 1, and stores the link into dst, which must be a field or subfield
in the syntax described under Field Specifications above.
The bundle or bundle_load actions are usually easier to use than multipath.
fields must be one of the following:
eth_src
Hashes Ethernet source address only.
symmetric_l4
Hashes Ethernet source, destination, and type, VLAN ID, IPv4/IPv6 source,
destination, and protocol, and TCP or SCTP (but not UDP) ports. The hash is
computed so that pairs of corresponding flows in each direction hash to the same
value, in environments where L2 paths are the same in each direction. UDP ports
are not included in the hash to support protocols such as VXLAN that use
asymmetric ports in each direction.
symmetric_l3l4
Hashes IPv4/IPv6 source, destination, and protocol, and TCP or SCTP (but not
UDP) ports. Like symmetric_l4, this is a symmetric hash, but by excluding L2
headers it is more effective in environments with asymmetric L2 paths (e.g.
paths involving VRRP IP addresses on a router). Not an effective hash function
for protocols other than IPv4 and IPv6, which hash to a constant zero.
symmetric_l3l4+udp
Like symmetric_l3l4+udp, but UDP ports are included in the hash. This is a more
effective hash when asymmetric UDP protocols such as VXLAN are not a
consideration.
symmetric_l3
Hashes network source address and network destination address.
nw_src Hashes network source address only.
nw_dst Hashes network destination address only.
The algorithm used to compute the final result link must be one of the following:
modulo_n
Computes link = hash(flow) % n_links.
This algorithm redistributes all traffic when n_links changes. It has O(1)
performance.
Use 65535 for max_link to get a raw hash value.
This algorithm is specified by RFC 2992.
hash_threshold
Computes link = hash(flow) / (MAX_HASH / n_links).
Redistributes between one-quarter and one-half of traffic when n_links changes.
It has O(1) performance.
This algorithm is specified by RFC 2992.
hrw (Highest Random Weight)
Computes the following:
for i in [0, n_links]:
weights[i] = hash(flow, i)
link = { i such that weights[i] >= weights[j] for all j != i }
Redistributes 1 / n_links of traffic when n_links changes. It has O(n_links)
performance. If n_links is greater than a threshold (currently 64, but subject
to change), Open vSwitch will substitute another algorithm automatically.
This algorithm is specified by RFC 2992.
iter_hash (Iterative Hash)
Computes the following:
i = 0
repeat:
i = i + 1
link = hash(flow, i) % arg
while link > max_link
Redistributes 1 / n_links of traffic when n_links changes. O(1) performance
when arg / max_link is bounded by a constant.
Redistributes all traffic when arg changes.
arg must be greater than max_link and for best performance should be no more
than approximately max_link * 2. If arg is outside the acceptable range, Open
vSwitch will automatically substitute the least power of 2 greater than
max_link.
This algorithm is specific to Open vSwitch.
Only the iter_hash algorithm uses arg.
It is an error if max_link is greater than or equal to 2**n_bits.
Conformance
This is an OpenFlow extension added in Open vSwitch 1.1.
OTHER ACTIONS
The conjunction action
Syntax:
conjunction(id, k/n)
This action allows for sophisticated conjunctive match flows. Refer to Conjunctive Match
Fields in ovs-fields(7) for details.
A flow that has one or more conjunction actions may not have any other actions except for
note actions.
Conformance
Open vSwitch 2.4 introduced the conjunction action and conj_id field. They are
Open vSwitch extensions to OpenFlow.
The note action
Syntax:
note:[hh]...
This action does nothing at all. OpenFlow controllers may use it to annotate flows with
more data than can fit in a flow cookie.
The action may include any number of bytes represented as hex digits hh. Periods may
separate pairs of hex digits, for readability. The note action’s format doesn’t include
an exact length for its payload, so the provided bytes will be padded on the right by
enough bytes with value 0 to make the total number 6 more than a multiple of 8.
Conformance
This action is an extension to OpenFlow introduced in Open vSwitch 1.1.
The sample action
Syntax:
sample(argument...)
Samples packets and sends one sample for every sampled packet.
The following argument forms are accepted:
probability=packets
The number of sampled packets out of 65535. Must be greater or equal to 1.
collector_set_id=id
The unsigned 32-bit integer identifier of the set of sample collectors to send
sampled packets to. Defaults to 0.
obs_domain_id=value
When sending samples to IPFIX collectors, the unsigned 32-bit integer
Observation Domain ID sent in every IPFIX flow record. The value may be
specified as a 32-bit integer or a field or subfield in the syntax described
under Field Specifications above. Defaults to 0.
obs_point_id=value
When sending samples to IPFIX collectors, the unsigned 32-bit integer
Observation Point ID sent in every IPFIX flow record. The value may be specified
as a 32-bit integer or a field or subfield in the syntax described under Field
Specifications above. Defaults to 0.
sampling_port=port
Sample packets on port, which should be the ingress or egress port. This
option, which was added in Open vSwitch 2.6, allows the IPFIX implementation to
export egress tunnel information.
ingress
egress Specifies explicitly that the packet is being sampled on ingress to or egress
from the switch. IPFIX reports sent by Open vSwitch before version 2.6 did not
include a direction. From 2.6 until 2.7, IPFIX reports inferred a direction
from sampling_port: if it was the packet’s output port, then the direction was
reported as egress, otherwise as ingress. Open vSwitch 2.7 introduced these
options, which allow the inferred direction to be overridden. This is
particularly useful when the ingress (or egress) port is not a tunnel.
Refer to ovs-vswitchd.conf.db(5) for more details on configuring sample collector sets.
Conformance
This action is an OpenFlow extension added in Open vSwitch 2.4.
Support for subfields in obs_domain_id and obs_point_id was added in Open vSwitch
3.4.
INSTRUCTIONS
Every version of OpenFlow includes actions. OpenFlow 1.1 introduced the higher-level,
related concept of instructions. In OpenFlow 1.1 and later, actions within a flow are
always encapsulated within an instruction. Each flow has at most one instruction of each
kind, which are executed in the following fixed order defined in the OpenFlow
specification:
1. Meter
2. Apply-Actions
3. Clear-Actions
4. Write-Actions
5. Write-Metadata
6. Stat-Trigger (not supported by Open vSwitch)
7. Goto-Table
The most important instruction is Apply-Actions. This instruction encapsulates any number
of actions, which the instruction executes. Open vSwitch does not explicitly represent
Apply-Actions. Instead, any action by itself is implicitly part of an Apply-Actions
instructions.
Open vSwitch syntax requires other instructions, if present, to be in the order listed
above. Otherwise it will flag an error.
The meter action and instruction
Syntax:
meter:meter_id
Apply meter meter_id. If a meter band rate is exceeded, the packet may be dropped, or
modified, depending on the meter band type.
Conformance
OpenFlow 1.3 introduced the meter instruction. OpenFlow 1.5 changes meter from an
instruction to an action.
OpenFlow 1.5 allows implementations to restrict meter to be the first action in an
action list and to exclude meter from action sets, for better compatibility with
OpenFlow 1.3 and 1.4. Open vSwitch restricts the meter action both ways.
Open vSwitch 2.0 introduced OpenFlow protocol support for meters, but it did not
include a datapath implementation. Open vSwitch 2.7 added meter support to the
userspace datapath. Open vSwitch 2.10 added meter support to the kernel datapath.
Open vSwitch 2.12 added support for meter as an action in OpenFlow 1.5.
The clear_actions instruction
Syntax:
clear_actions
Clears the action set. See Action Sets, above, for more information.
Conformance
OpenFlow 1.1 introduced clear_actions. Open vSwitch 2.1 added support for
clear_actions.
The write_actions instruction
Syntax:
write_actions(action...)
Adds each action to the action set. The action set is carried between flow tables and
then executed at the end of the pipeline. Only certain actions may be written to the
action set. See Action Sets, above, for more information.
Conformance
OpenFlow 1.1 introduced write_actions. Open vSwitch 2.1 added support for
write_actions.
The write_metadata instruction
Syntax:
write_metadata:value[/mask]
Updates the flow’s metadata field. If mask is omitted, metadata is set exactly to value;
if mask is specified, then a 1-bit in mask indicates that the corresponding bit in
metadata will be replaced with the corresponding bit from value. Both value and mask are
64-bit values that are decimal by default; use a 0x prefix to specify them in hexadecimal.
The metadata field can also be matched in the flow table and updated with actions such as
set_field and move.
Conformance
OpenFlow 1.1 introduced write_metadata. Open vSwitch 2.1 added support for
write_metadata.
The goto_table instruction
Syntax:
goto_table:table
Jumps to table as the next table in the process pipeline. The table may be a number
between 0 and 254 or a table name.
It is an error if table is less than or equal to the table of the flow that contains it;
that is, goto_table must move forward in the OpenFlow pipeline. Since goto_table must be
the last instruction in a flow, it never leads to recursion. The resubmit extension
action is more flexible.
Conformance
OpenFlow 1.1 introduced goto_table. Open vSwitch 2.1 added support for goto_table.
AUTHOR
The Open vSwitch Development Community
COPYRIGHT
2016-2024, The Open vSwitch Development Community