Provided by: ovn-central_20.03.2-0ubuntu0.20.04.5_amd64 
NAME
ovn-northd - Open Virtual Network central control daemon
SYNOPSIS
ovn-northd [options]
DESCRIPTION
ovn-northd is a centralized daemon responsible for translating the high-level OVN
configuration into logical configuration consumable by daemons such as ovn-controller. It
translates the logical network configuration in terms of conventional network concepts,
taken from the OVN Northbound Database (see ovn-nb(5)), into logical datapath flows in the
OVN Southbound Database (see ovn-sb(5)) below it.
OPTIONS
--ovnnb-db=database
The OVSDB database containing the OVN Northbound Database. If the OVN_NB_DB
environment variable is set, its value is used as the default. Otherwise, the
default is unix:/ovnnb_db.sock.
--ovnsb-db=database
The OVSDB database containing the OVN Southbound Database. If the OVN_SB_DB
environment variable is set, its value is used as the default. Otherwise, the
default is unix:/ovnsb_db.sock.
database in the above options must be an OVSDB active or passive connection method, as
described in ovsdb(7).
Daemon Options
--pidfile[=pidfile]
Causes a file (by default, program.pid) to be created indicating the PID of the
running process. If the pidfile argument is not specified, or if it does not begin
with /, then it is created in .
If --pidfile is not specified, no pidfile is created.
--overwrite-pidfile
By default, when --pidfile is specified and the specified pidfile already exists
and is locked by a running process, the daemon refuses to start. Specify
--overwrite-pidfile to cause it to instead overwrite the pidfile.
When --pidfile is not specified, this option has no effect.
--detach
Runs this program as a background process. The process forks, and in the child it
starts a new session, closes the standard file descriptors (which has the side
effect of disabling logging to the console), and changes its current directory to
the root (unless --no-chdir is specified). After the child completes its
initialization, the parent exits.
--monitor
Creates an additional process to monitor this program. If it dies due to a signal
that indicates a programming error (SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL,
SIGPIPE, SIGSEGV, SIGXCPU, or SIGXFSZ) then the monitor process starts a new copy
of it. If the daemon dies or exits for another reason, the monitor process exits.
This option is normally used with --detach, but it also functions without it.
--no-chdir
By default, when --detach is specified, the daemon changes its current working
directory to the root directory after it detaches. Otherwise, invoking the daemon
from a carelessly chosen directory would prevent the administrator from unmounting
the file system that holds that directory.
Specifying --no-chdir suppresses this behavior, preventing the daemon from changing
its current working directory. This may be useful for collecting core files, since
it is common behavior to write core dumps into the current working directory and
the root directory is not a good directory to use.
This option has no effect when --detach is not specified.
--no-self-confinement
By default this daemon will try to self-confine itself to work with files under
well-known directories whitelisted at build time. It is better to stick with this
default behavior and not to use this flag unless some other Access Control is used
to confine daemon. Note that in contrast to other access control implementations
that are typically enforced from kernel-space (e.g. DAC or MAC), self-confinement
is imposed from the user-space daemon itself and hence should not be considered as
a full confinement strategy, but instead should be viewed as an additional layer of
security.
--user=user:group
Causes this program to run as a different user specified in user:group, thus
dropping most of the root privileges. Short forms user and :group are also allowed,
with current user or group assumed, respectively. Only daemons started by the root
user accepts this argument.
On Linux, daemons will be granted CAP_IPC_LOCK and CAP_NET_BIND_SERVICES before
dropping root privileges. Daemons that interact with a datapath, such as
ovs-vswitchd, will be granted three additional capabilities, namely CAP_NET_ADMIN,
CAP_NET_BROADCAST and CAP_NET_RAW. The capability change will apply even if the new
user is root.
On Windows, this option is not currently supported. For security reasons,
specifying this option will cause the daemon process not to start.
Logging Options
-v[spec]
--verbose=[spec]
Sets logging levels. Without any spec, sets the log level for every module and
destination to dbg. Otherwise, spec is a list of words separated by spaces or commas
or colons, up to one from each category below:
• A valid module name, as displayed by the vlog/list command on ovs-appctl(8),
limits the log level change to the specified module.
• syslog, console, or file, to limit the log level change to only to the system
log, to the console, or to a file, respectively. (If --detach is specified,
the daemon closes its standard file descriptors, so logging to the console
will have no effect.)
On Windows platform, syslog is accepted as a word and is only useful along
with the --syslog-target option (the word has no effect otherwise).
• off, emer, err, warn, info, or dbg, to control the log level. Messages of the
given severity or higher will be logged, and messages of lower severity will
be filtered out. off filters out all messages. See ovs-appctl(8) for a
definition of each log level.
Case is not significant within spec.
Regardless of the log levels set for file, logging to a file will not take place
unless --log-file is also specified (see below).
For compatibility with older versions of OVS, any is accepted as a word but has no
effect.
-v
--verbose
Sets the maximum logging verbosity level, equivalent to --verbose=dbg.
-vPATTERN:destination:pattern
--verbose=PATTERN:destination:pattern
Sets the log pattern for destination to pattern. Refer to ovs-appctl(8) for a
description of the valid syntax for pattern.
-vFACILITY:facility
--verbose=FACILITY:facility
Sets the RFC5424 facility of the log message. facility can be one of kern, user,
mail, daemon, auth, syslog, lpr, news, uucp, clock, ftp, ntp, audit, alert, clock2,
local0, local1, local2, local3, local4, local5, local6 or local7. If this option is
not specified, daemon is used as the default for the local system syslog and local0
is used while sending a message to the target provided via the --syslog-target
option.
--log-file[=file]
Enables logging to a file. If file is specified, then it is used as the exact name
for the log file. The default log file name used if file is omitted is
/var/log/ovn/program.log.
--syslog-target=host:port
Send syslog messages to UDP port on host, in addition to the system syslog. The host
must be a numerical IP address, not a hostname.
--syslog-method=method
Specify method as how syslog messages should be sent to syslog daemon. The following
forms are supported:
• libc, to use the libc syslog() function. Downside of using this options is
that libc adds fixed prefix to every message before it is actually sent to the
syslog daemon over /dev/log UNIX domain socket.
• unix:file, to use a UNIX domain socket directly. It is possible to specify
arbitrary message format with this option. However, rsyslogd 8.9 and older
versions use hard coded parser function anyway that limits UNIX domain socket
use. If you want to use arbitrary message format with older rsyslogd versions,
then use UDP socket to localhost IP address instead.
• udp:ip:port, to use a UDP socket. With this method it is possible to use
arbitrary message format also with older rsyslogd. When sending syslog
messages over UDP socket extra precaution needs to be taken into account, for
example, syslog daemon needs to be configured to listen on the specified UDP
port, accidental iptables rules could be interfering with local syslog traffic
and there are some security considerations that apply to UDP sockets, but do
not apply to UNIX domain sockets.
• null, to discard all messages logged to syslog.
The default is taken from the OVS_SYSLOG_METHOD environment variable; if it is unset,
the default is libc.
PKI Options
PKI configuration is required in order to use SSL for the connections to the Northbound
and Southbound databases.
-p privkey.pem
--private-key=privkey.pem
Specifies a PEM file containing the private key used as identity for outgoing
SSL connections.
-c cert.pem
--certificate=cert.pem
Specifies a PEM file containing a certificate that certifies the private key
specified on -p or --private-key to be trustworthy. The certificate must be
signed by the certificate authority (CA) that the peer in SSL connections will
use to verify it.
-C cacert.pem
--ca-cert=cacert.pem
Specifies a PEM file containing the CA certificate for verifying certificates
presented to this program by SSL peers. (This may be the same certificate that
SSL peers use to verify the certificate specified on -c or --certificate, or
it may be a different one, depending on the PKI design in use.)
-C none
--ca-cert=none
Disables verification of certificates presented by SSL peers. This introduces
a security risk, because it means that certificates cannot be verified to be
those of known trusted hosts.
Other Options
--unixctl=socket
Sets the name of the control socket on which program listens for runtime management
commands (see RUNTIME MANAGEMENT COMMANDS, below). If socket does not begin with /,
it is interpreted as relative to . If --unixctl is not used at all, the default
socket is /program.pid.ctl, where pid is program’s process ID.
On Windows a local named pipe is used to listen for runtime management commands. A
file is created in the absolute path as pointed by socket or if --unixctl is not
used at all, a file is created as program in the configured OVS_RUNDIR directory.
The file exists just to mimic the behavior of a Unix domain socket.
Specifying none for socket disables the control socket feature.
-h
--help
Prints a brief help message to the console.
-V
--version
Prints version information to the console.
RUNTIME MANAGEMENT COMMANDS
ovs-appctl can send commands to a running ovn-northd process. The currently supported
commands are described below.
exit Causes ovn-northd to gracefully terminate.
pause Pauses the ovn-northd operation from processing any Northbound and
Southbound database changes. This will also instruct ovn-northd to drop any
lock on SB DB.
resume Resumes the ovn-northd operation to process Northbound and Southbound
database contents and generate logical flows. This will also instruct ovn-
northd to aspire for the lock on SB DB.
is-paused
Returns "true" if ovn-northd is currently paused, "false" otherwise.
status Prints this server’s status. Status will be "active" if ovn-northd has
acquired OVSDB lock on SB DB, "standby" if it has not or "paused" if this
instance is paused.
ACTIVE-STANDBY FOR HIGH AVAILABILITY
You may run ovn-northd more than once in an OVN deployment. When connected to a standalone
or clustered DB setup, OVN will automatically ensure that only one of them is active at a
time. If multiple instances of ovn-northd are running and the active ovn-northd fails, one
of the hot standby instances of ovn-northd will automatically take over.
Active-Standby with multiple OVN DB servers
You may run multiple OVN DB servers in an OVN deployment with:
• OVN DB servers deployed in active/passive mode with one active and multiple
passive ovsdb-servers.
• ovn-northd also deployed on all these nodes, using unix ctl sockets to
connect to the local OVN DB servers.
In such deployments, the ovn-northds on the passive nodes will process the DB changes and
compute logical flows to be thrown out later, because write transactions are not allowed
by the passive ovsdb-servers. It results in unnecessary CPU usage.
With the help of runtime management command pause, you can pause ovn-northd on these
nodes. When a passive node becomes master, you can use the runtime management command
resume to resume the ovn-northd to process the DB changes.
LOGICAL FLOW TABLE STRUCTURE
One of the main purposes of ovn-northd is to populate the Logical_Flow table in the
OVN_Southbound database. This section describes how ovn-northd does this for switch and
router logical datapaths.
Logical Switch Datapaths
Ingress Table 0: Admission Control and Ingress Port Security - L2
Ingress table 0 contains these logical flows:
• Priority 100 flows to drop packets with VLAN tags or multicast Ethernet
source addresses.
• Priority 50 flows that implement ingress port security for each enabled
logical port. For logical ports on which port security is enabled, these
match the inport and the valid eth.src address(es) and advance only those
packets to the next flow table. For logical ports on which port security is
not enabled, these advance all packets that match the inport.
There are no flows for disabled logical ports because the default-drop behavior of logical
flow tables causes packets that ingress from them to be dropped.
Ingress Table 1: Ingress Port Security - IP
Ingress table 1 contains these logical flows:
• For each element in the port security set having one or more IPv4 or IPv6
addresses (or both),
• Priority 90 flow to allow IPv4 traffic if it has IPv4 addresses which
match the inport, valid eth.src and valid ip4.src address(es).
• Priority 90 flow to allow IPv4 DHCP discovery traffic if it has a
valid eth.src. This is necessary since DHCP discovery messages are
sent from the unspecified IPv4 address (0.0.0.0) since the IPv4
address has not yet been assigned.
• Priority 90 flow to allow IPv6 traffic if it has IPv6 addresses which
match the inport, valid eth.src and valid ip6.src address(es).
• Priority 90 flow to allow IPv6 DAD (Duplicate Address Detection)
traffic if it has a valid eth.src. This is is necessary since DAD
include requires joining an multicast group and sending neighbor
solicitations for the newly assigned address. Since no address is yet
assigned, these are sent from the unspecified IPv6 address (::).
• Priority 80 flow to drop IP (both IPv4 and IPv6) traffic which match
the inport and valid eth.src.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 2: Ingress Port Security - Neighbor discovery
Ingress table 2 contains these logical flows:
• For each element in the port security set,
• Priority 90 flow to allow ARP traffic which match the inport and
valid eth.src and arp.sha. If the element has one or more IPv4
addresses, then it also matches the valid arp.spa.
• Priority 90 flow to allow IPv6 Neighbor Solicitation and
Advertisement traffic which match the inport, valid eth.src and
nd.sll/nd.tll. If the element has one or more IPv6 addresses, then it
also matches the valid nd.target address(es) for Neighbor
Advertisement traffic.
• Priority 80 flow to drop ARP and IPv6 Neighbor Solicitation and
Advertisement traffic which match the inport and valid eth.src.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 3: from-lport Pre-ACLs
This table prepares flows for possible stateful ACL processing in ingress table ACLs. It
contains a priority-0 flow that simply moves traffic to the next table. If stateful ACLs
are used in the logical datapath, a priority-100 flow is added that sets a hint (with
reg0[0] = 1; next;) for table Pre-stateful to send IP packets to the connection tracker
before eventually advancing to ingress table ACLs. If special ports such as route ports or
localnet ports can’t use ct(), a priority-110 flow is added to skip over stateful ACLs.
IPv6 Neighbor Discovery and MLD traffic also skips stateful ACLs.
This table also has a priority-110 flow with the match eth.dst == E for all logical switch
datapaths to move traffic to the next table. Where E is the service monitor mac defined in
the options:svc_monitor_mac colum of NB_Global table.
Ingress Table 4: Pre-LB
This table prepares flows for possible stateful load balancing processing in ingress table
LB and Stateful. It contains a priority-0 flow that simply moves traffic to the next
table. Moreover it contains a priority-110 flow to move IPv6 Neighbor Discovery and MLD
traffic to the next table. If load balancing rules with virtual IP addresses (and ports)
are configured in OVN_Northbound database for a logical switch datapath, a priority-100
flow is added for each configured virtual IP address VIP. For IPv4 VIPs, the match is ip
&& ip4.dst == VIP. For IPv6 VIPs, the match is ip && ip6.dst == VIP. The flow sets an
action reg0[0] = 1; next; to act as a hint for table Pre-stateful to send IP packets to
the connection tracker for packet de-fragmentation before eventually advancing to ingress
table LB. If controller_event has been enabled and load balancing rules with empty
backends have been added in OVN_Northbound, a 130 flow is added to trigger ovn-controller
events whenever the chassis receives a packet for that particular VIP. If event-elb meter
has been previously created, it will be associated to the empty_lb logical flow
This table also has a priority-110 flow with the match eth.dst == E for all logical switch
datapaths to move traffic to the next table. Where E is the service monitor mac defined in
the options:svc_monitor_mac colum of NB_Global table.
Ingress Table 5: Pre-stateful
This table prepares flows for all possible stateful processing in next tables. It contains
a priority-0 flow that simply moves traffic to the next table. A priority-100 flow sends
the packets to connection tracker based on a hint provided by the previous tables (with a
match for reg0[0] == 1) by using the ct_next; action.
Ingress table 6: from-lport ACLs
Logical flows in this table closely reproduce those in the ACL table in the OVN_Northbound
database for the from-lport direction. The priority values from the ACL table have a
limited range and have 1000 added to them to leave room for OVN default flows at both
higher and lower priorities.
• allow ACLs translate into logical flows with the next; action. If there are
any stateful ACLs on this datapath, then allow ACLs translate to ct_commit;
next; (which acts as a hint for the next tables to commit the connection to
conntrack),
• allow-related ACLs translate into logical flows with the
ct_commit(ct_label=0/1); next; actions for new connections and reg0[1] = 1;
next; for existing connections.
• reject ACLs translate into logical flows with the tcp_reset { output <->
inport; next(pipeline=egress,table=5);} action for TCP connections and
icmp4/icmp6 action for UDP connections.
• Other ACLs translate to drop; for new or untracked connections and
ct_commit(ct_label=1/1); for known connections. Setting ct_label marks a
connection as one that was previously allowed, but should no longer be
allowed due to a policy change.
This table also contains a priority 0 flow with action next;, so that ACLs allow packets
by default. If the logical datapath has a statetful ACL, the following flows will also be
added:
• A priority-1 flow that sets the hint to commit IP traffic to the connection
tracker (with action reg0[1] = 1; next;). This is needed for the default
allow policy because, while the initiator’s direction may not have any
stateful rules, the server’s may and then its return traffic would not be
known and marked as invalid.
• A priority-65535 flow that allows any traffic in the reply direction for a
connection that has been committed to the connection tracker (i.e.,
established flows), as long as the committed flow does not have
ct_label.blocked set. We only handle traffic in the reply direction here
because we want all packets going in the request direction to still go
through the flows that implement the currently defined policy based on ACLs.
If a connection is no longer allowed by policy, ct_label.blocked will get
set and packets in the reply direction will no longer be allowed, either.
• A priority-65535 flow that allows any traffic that is considered related to
a committed flow in the connection tracker (e.g., an ICMP Port Unreachable
from a non-listening UDP port), as long as the committed flow does not have
ct_label.blocked set.
• A priority-65535 flow that drops all traffic marked by the connection
tracker as invalid.
• A priority-65535 flow that drops all traffic in the reply direction with
ct_label.blocked set meaning that the connection should no longer be allowed
due to a policy change. Packets in the request direction are skipped here to
let a newly created ACL re-allow this connection.
• A priority-65535 flow that allows IPv6 Neighbor solicitation, Neighbor
discover, Router solicitation, Router advertisement and MLD packets.
• A priority 34000 logical flow is added for each logical switch datapath with
the match eth.dst = E to allow the service monitor reply packet destined to
ovn-controller with the action next, where E is the service monitor mac
defined in the options:svc_monitor_mac colum of NB_Global table.
Ingress Table 7: from-lport QoS Marking
Logical flows in this table closely reproduce those in the QoS table with the action
column set in the OVN_Northbound database for the from-lport direction.
• For every qos_rules entry in a logical switch with DSCP marking enabled, a
flow will be added at the priority mentioned in the QoS table.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 8: from-lport QoS Meter
Logical flows in this table closely reproduce those in the QoS table with the bandwidth
column set in the OVN_Northbound database for the from-lport direction.
• For every qos_rules entry in a logical switch with metering enabled, a flow
will be added at the priorirty mentioned in the QoS table.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 9: LB
It contains a priority-0 flow that simply moves traffic to the next table. For established
connections a priority 100 flow matches on ct.est && !ct.rel && !ct.new && !ct.inv and
sets an action reg0[2] = 1; next; to act as a hint for table Stateful to send packets
through connection tracker to NAT the packets. (The packet will automatically get DNATed
to the same IP address as the first packet in that connection.)
Ingress Table 10: Stateful
• For all the configured load balancing rules for a switch in OVN_Northbound
database that includes a L4 port PORT of protocol P and IP address VIP, a
priority-120 flow is added. For IPv4 VIPs , the flow matches ct.new && ip &&
ip4.dst == VIP && P && P.dst == PORT. For IPv6 VIPs, the flow matches ct.new
&& ip && ip6.dst == VIP && P && P.dst == PORT. The flow’s action is
ct_lb(args) , where args contains comma separated IP addresses (and optional
port numbers) to load balance to. The address family of the IP addresses of
args is the same as the address family of VIP. If health check is enabled,
then args will only contain those endpoints whose service monitor status
entry in OVN_Southbound db is either online or empty.
• For all the configured load balancing rules for a switch in OVN_Northbound
database that includes just an IP address VIP to match on, OVN adds a
priority-110 flow. For IPv4 VIPs, the flow matches ct.new && ip && ip4.dst
== VIP. For IPv6 VIPs, the flow matches ct.new && ip && ip6.dst == VIP. The
action on this flow is ct_lb(args), where args contains comma separated IP
addresses of the same address family as VIP.
• A priority-100 flow commits packets to connection tracker using ct_commit;
next; action based on a hint provided by the previous tables (with a match
for reg0[1] == 1).
• A priority-100 flow sends the packets to connection tracker using ct_lb; as
the action based on a hint provided by the previous tables (with a match for
reg0[2] == 1).
• A priority-0 flow that simply moves traffic to the next table.
Ingress Table 11: Pre-Hairpin
• For all configured load balancer VIPs a priority-2 flow that matches on
traffic that needs to be hairpinned, i.e., after load balancing the
destination IP matches the source IP, which sets reg0[6] = 1 and executes
ct_snat(VIP) to force replies to these packets to come back through OVN.
• For all configured load balancer VIPs a priority-1 flow that matches on
replies to hairpinned traffic, i.e., destination IP is VIP, source IP is the
backend IP and source L4 port is backend port, which sets reg0[6] = 1 and
executes ct_snat;.
• A priority-0 flow that simply moves traffic to the next table.
Ingress Table 12: Hairpin
• A priority-1 flow that hairpins traffic matched by non-default flows in the
Pre-Hairpin table. Hairpinning is done at L2, Ethernet addresses are swapped
and the packets are looped back on the input port.
• A priority-0 flow that simply moves traffic to the next table.
Ingress Table 13: ARP/ND responder
This table implements ARP/ND responder in a logical switch for known IPs. The advantage of
the ARP responder flow is to limit ARP broadcasts by locally responding to ARP requests
without the need to send to other hypervisors. One common case is when the inport is a
logical port associated with a VIF and the broadcast is responded to on the local
hypervisor rather than broadcast across the whole network and responded to by the
destination VM. This behavior is proxy ARP.
ARP requests arrive from VMs from a logical switch inport of type default. For this case,
the logical switch proxy ARP rules can be for other VMs or logical router ports. Logical
switch proxy ARP rules may be programmed both for mac binding of IP addresses on other
logical switch VIF ports (which are of the default logical switch port type, representing
connectivity to VMs or containers), and for mac binding of IP addresses on logical switch
router type ports, representing their logical router port peers. In order to support proxy
ARP for logical router ports, an IP address must be configured on the logical switch
router type port, with the same value as the peer logical router port. The configured MAC
addresses must match as well. When a VM sends an ARP request for a distributed logical
router port and if the peer router type port of the attached logical switch does not have
an IP address configured, the ARP request will be broadcast on the logical switch. One of
the copies of the ARP request will go through the logical switch router type port to the
logical router datapath, where the logical router ARP responder will generate a reply. The
MAC binding of a distributed logical router, once learned by an associated VM, is used for
all that VM’s communication needing routing. Hence, the action of a VM re-arping for the
mac binding of the logical router port should be rare.
Logical switch ARP responder proxy ARP rules can also be hit when receiving ARP requests
externally on a L2 gateway port. In this case, the hypervisor acting as an L2 gateway,
responds to the ARP request on behalf of a destination VM.
Note that ARP requests received from localnet or vtep logical inports can either go
directly to VMs, in which case the VM responds or can hit an ARP responder for a logical
router port if the packet is used to resolve a logical router port next hop address. In
either case, logical switch ARP responder rules will not be hit. It contains these logical
flows:
• Priority-100 flows to skip the ARP responder if inport is of type localnet
or vtep and advances directly to the next table. ARP requests sent to
localnet or vtep ports can be received by multiple hypervisors. Now, because
the same mac binding rules are downloaded to all hypervisors, each of the
multiple hypervisors will respond. This will confuse L2 learning on the
source of the ARP requests. ARP requests received on an inport of type
router are not expected to hit any logical switch ARP responder flows.
However, no skip flows are installed for these packets, as there would be
some additional flow cost for this and the value appears limited.
• If inport V is of type virtual adds a priority-100 logical flow for each P
configured in the options:virtual-parents column with the match
inport == P && && ((arp.op == 1 && arp.spa == VIP && arp.tpa == VIP) || (arp.op == 2 && arp.spa == VIP))
and applies the action
bind_vport(V, inport);
and advances the packet to the next table.
Where VIP is the virtual ip configured in the column options:virtual-ip.
• Priority-50 flows that match ARP requests to each known IP address A of
every logical switch port, and respond with ARP replies directly with
corresponding Ethernet address E:
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
These flows are omitted for logical ports (other than router ports or
localport ports) that are down, for logical ports of type virtual and for
logical ports with ’unknown’ address set.
• Priority-50 flows that match IPv6 ND neighbor solicitations to each known IP
address A (and A’s solicited node address) of every logical switch port
except of type router, and respond with neighbor advertisements directly
with corresponding Ethernet address E:
nd_na {
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
Priority-50 flows that match IPv6 ND neighbor solicitations to each known IP
address A (and A’s solicited node address) of logical switch port of type
router, and respond with neighbor advertisements directly with corresponding
Ethernet address E:
nd_na_router {
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
These flows are omitted for logical ports (other than router ports or
localport ports) that are down and for logical ports of type virtual.
• Priority-100 flows with match criteria like the ARP and ND flows above,
except that they only match packets from the inport that owns the IP
addresses in question, with action next;. These flows prevent OVN from
replying to, for example, an ARP request emitted by a VM for its own IP
address. A VM only makes this kind of request to attempt to detect a
duplicate IP address assignment, so sending a reply will prevent the VM from
accepting the IP address that it owns.
In place of next;, it would be reasonable to use drop; for the flows’
actions. If everything is working as it is configured, then this would
produce equivalent results, since no host should reply to the request. But
ARPing for one’s own IP address is intended to detect situations where the
network is not working as configured, so dropping the request would
frustrate that intent.
• For each SVC_MON_SRC_IP defined in the value of the
ip_port_mappings:ENDPOINT_IP column of Load_Balancer table, priority-110
logical flow is added with the match arp.tpa == SVC_MON_SRC_IP && && arp.op
== 1 and applies the action
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
where E is the service monitor source mac defined in the
options:svc_monitor_mac column in the NB_Global table. This mac is used as
the source mac in the service monitor packets for the load balancer endpoint
IP health checks.
SVC_MON_SRC_IP is used as the source ip in the service monitor IPv4 packets
for the load balancer endpoint IP health checks.
These flows are required if an ARP request is sent for the IP
SVC_MON_SRC_IP.
• For each VIP configured in the table Forwarding_Group a priority-50 logical
flow is added with the match arp.tpa == vip && && arp.op == 1
and applies the action
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
where E is the forwarding group’s mac defined in the vmac.
A is used as either the destination ip for load balancing traffic to child
ports or as nexthop to hosts behind the child ports.
These flows are required to respond to an ARP request if an ARP request is
sent for the IP vip.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 14: DHCP option processing
This table adds the DHCPv4 options to a DHCPv4 packet from the logical ports configured
with IPv4 address(es) and DHCPv4 options, and similarly for DHCPv6 options. This table
also adds flows for the logical ports of type external.
• A priority-100 logical flow is added for these logical ports which matches
the IPv4 packet with udp.src = 68 and udp.dst = 67 and applies the action
put_dhcp_opts and advances the packet to the next table.
reg0[3] = put_dhcp_opts(offer_ip = ip, options...);
next;
For DHCPDISCOVER and DHCPREQUEST, this transforms the packet into a DHCP
reply, adds the DHCP offer IP ip and options to the packet, and stores 1
into reg0[3]. For other kinds of packets, it just stores 0 into reg0[3].
Either way, it continues to the next table.
• A priority-100 logical flow is added for these logical ports which matches
the IPv6 packet with udp.src = 546 and udp.dst = 547 and applies the action
put_dhcpv6_opts and advances the packet to the next table.
reg0[3] = put_dhcpv6_opts(ia_addr = ip, options...);
next;
For DHCPv6 Solicit/Request/Confirm packets, this transforms the packet into
a DHCPv6 Advertise/Reply, adds the DHCPv6 offer IP ip and options to the
packet, and stores 1 into reg0[3]. For other kinds of packets, it just
stores 0 into reg0[3]. Either way, it continues to the next table.
• A priority-0 flow that matches all packets to advances to table 15.
Ingress Table 15: DHCP responses
This table implements DHCP responder for the DHCP replies generated by the previous table.
• A priority 100 logical flow is added for the logical ports configured with
DHCPv4 options which matches IPv4 packets with udp.src == 68 && udp.dst ==
67 && reg0[3] == 1 and responds back to the inport after applying these
actions. If reg0[3] is set to 1, it means that the action put_dhcp_opts was
successful.
eth.dst = eth.src;
eth.src = E;
ip4.src = S;
udp.src = 67;
udp.dst = 68;
outport = P;
flags.loopback = 1;
output;
where E is the server MAC address and S is the server IPv4 address defined
in the DHCPv4 options. Note that ip4.dst field is handled by put_dhcp_opts.
(This terminates ingress packet processing; the packet does not go to the
next ingress table.)
• A priority 100 logical flow is added for the logical ports configured with
DHCPv6 options which matches IPv6 packets with udp.src == 546 && udp.dst ==
547 && reg0[3] == 1 and responds back to the inport after applying these
actions. If reg0[3] is set to 1, it means that the action put_dhcpv6_opts
was successful.
eth.dst = eth.src;
eth.src = E;
ip6.dst = A;
ip6.src = S;
udp.src = 547;
udp.dst = 546;
outport = P;
flags.loopback = 1;
output;
where E is the server MAC address and S is the server IPv6 LLA address
generated from the server_id defined in the DHCPv6 options and A is the IPv6
address defined in the logical port’s addresses column.
(This terminates packet processing; the packet does not go on the next
ingress table.)
• A priority-0 flow that matches all packets to advances to table 16.
Ingress Table 16 DNS Lookup
This table looks up and resolves the DNS names to the corresponding configured IP
address(es).
• A priority-100 logical flow for each logical switch datapath if it is
configured with DNS records, which matches the IPv4 and IPv6 packets with
udp.dst = 53 and applies the action dns_lookup and advances the packet to
the next table.
reg0[4] = dns_lookup(); next;
For valid DNS packets, this transforms the packet into a DNS reply if the
DNS name can be resolved, and stores 1 into reg0[4]. For failed DNS
resolution or other kinds of packets, it just stores 0 into reg0[4]. Either
way, it continues to the next table.
Ingress Table 17 DNS Responses
This table implements DNS responder for the DNS replies generated by the previous table.
• A priority-100 logical flow for each logical switch datapath if it is
configured with DNS records, which matches the IPv4 and IPv6 packets with
udp.dst = 53 && reg0[4] == 1 and responds back to the inport after applying
these actions. If reg0[4] is set to 1, it means that the action dns_lookup
was successful.
eth.dst <-> eth.src;
ip4.src <-> ip4.dst;
udp.dst = udp.src;
udp.src = 53;
outport = P;
flags.loopback = 1;
output;
(This terminates ingress packet processing; the packet does not go to the
next ingress table.)
Ingress table 18 External ports
Traffic from the external logical ports enter the ingress datapath pipeline via the
localnet port. This table adds the below logical flows to handle the traffic from these
ports.
• A priority-100 flow is added for each external logical port which doesn’t
reside on a chassis to drop the ARP/IPv6 NS request to the router IP(s) (of
the logical switch) which matches on the inport of the external logical port
and the valid eth.src address(es) of the external logical port.
This flow guarantees that the ARP/NS request to the router IP address from
the external ports is responded by only the chassis which has claimed these
external ports. All the other chassis, drops these packets.
• A priority-0 flow that matches all packets to advances to table 19.
Ingress Table 19 Destination Lookup
This table implements switching behavior. It contains these logical flows:
• A priorirty-110 flow with the match eth.src == E for all logical switch
datapaths and applies the action handle_svc_check(inport). Where E is the
service monitor mac defined in the options:svc_monitor_mac colum of
NB_Global table.
• A priority-100 flow that punts all IGMP/MLD packets to ovn-controller if
multicast snooping is enabled on the logical switch. The flow also forwards
the IGMP/MLD packets to the MC_MROUTER_STATIC multicast group, which
ovn-northd populates with all the logical ports that have options
:mcast_flood_reports=’true’.
• Priority-90 flows that forward registered IP multicast traffic to their
corresponding multicast group, which ovn-northd creates based on learnt
IGMP_Group entries. The flows also forward packets to the MC_MROUTER_FLOOD
multicast group, which ovn-nortdh populates with all the logical ports that
are connected to logical routers with options:mcast_relay=’true’.
• A priority-85 flow that forwards all IP multicast traffic destined to
224.0.0.X to the MC_FLOOD multicast group, which ovn-northd populates with
all enabled logical ports.
• A priority-85 flow that forwards all IP multicast traffic destined to
reserved multicast IPv6 addresses (RFC 4291, 2.7.1, e.g., Solicited-Node
multicast) to the MC_FLOOD multicast group, which ovn-northd populates with
all enabled logical ports.
• A priority-80 flow that forwards all unregistered IP multicast traffic to
the MC_STATIC multicast group, which ovn-northd populates with all the
logical ports that have options :mcast_flood=’true’. The flow also forwards
unregistered IP multicast traffic to the MC_MROUTER_FLOOD multicast group,
which ovn-northd populates with all the logical ports connected to logical
routers that have options :mcast_relay=’true’.
• A priority-80 flow that drops all unregistered IP multicast traffic if
other_config :mcast_snoop=’true’ and other_config
:mcast_flood_unregistered=’false’ and the switch is not connected to a
logical router that has options :mcast_relay=’true’ and the switch doesn’t
have any logical port with options :mcast_flood=’true’.
• Priority-80 flows for each port connected to a logical router matching self
originated GARP/ARP request/ND packets. These packets are flooded to the
MC_FLOOD which contains all logical ports.
• Priority-75 flows for each IP address/VIP/NAT address owned by a router port
connected to the switch. These flows match ARP requests and ND packets for
the specific IP addresses. Matched packets are forwarded only to the router
that owns the IP address and, if present, to the localnet port of the
logical switch.
• A priority-70 flow that outputs all packets with an Ethernet broadcast or
multicast eth.dst to the MC_FLOOD multicast group.
• One priority-50 flow that matches each known Ethernet address against
eth.dst and outputs the packet to the single associated output port.
For the Ethernet address on a logical switch port of type router, when that
logical switch port’s addresses column is set to router and the connected
logical router port specifies a redirect-chassis:
• The flow for the connected logical router port’s Ethernet address is
only programmed on the redirect-chassis.
• If the logical router has rules specified in nat with external_mac,
then those addresses are also used to populate the switch’s
destination lookup on the chassis where logical_port is resident.
For the Ethernet address on a logical switch port of type router, when that
logical switch port’s addresses column is set to router and the connected
logical router port specifies a reside-on-redirect-chassis and the logical
router to which the connected logical router port belongs to has a
redirect-chassis distributed gateway logical router port:
• The flow for the connected logical router port’s Ethernet address is
only programmed on the redirect-chassis.
For each forwarding group configured on the logical switch datapath, a
priority-50 flow that matches on eth.dst == VIP
with an action of fwd_group(childports=args ), where args contains comma
separated logical switch child ports to load balance to. If liveness is
enabled, then action also includes liveness=true.
• One priority-0 fallback flow that matches all packets and outputs them to
the MC_UNKNOWN multicast group, which ovn-northd populates with all enabled
logical ports that accept unknown destination packets. As a small
optimization, if no logical ports accept unknown destination packets,
ovn-northd omits this multicast group and logical flow.
Egress Table 0: Pre-LB
This table is similar to ingress table Pre-LB. It contains a priority-0 flow that simply
moves traffic to the next table. Moreover it contains a priority-110 flow to move IPv6
Neighbor Discovery traffic to the next table. If any load balancing rules exist for the
datapath, a priority-100 flow is added with a match of ip and action of reg0[0] = 1; next;
to act as a hint for table Pre-stateful to send IP packets to the connection tracker for
packet de-fragmentation.
This table also has a priority-110 flow with the match eth.src == E for all logical switch
datapaths to move traffic to the next table. Where E is the service monitor mac defined in
the options:svc_monitor_mac colum of NB_Global table.
Egress Table 1: to-lport Pre-ACLs
This is similar to ingress table Pre-ACLs except for to-lport traffic.
This table also has a priority-110 flow with the match eth.src == E for all logical switch
datapaths to move traffic to the next table. Where E is the service monitor mac defined in
the options:svc_monitor_mac colum of NB_Global table.
Egress Table 2: Pre-stateful
This is similar to ingress table Pre-stateful.
Egress Table 3: LB
This is similar to ingress table LB.
Egress Table 4: to-lport ACLs
This is similar to ingress table ACLs except for to-lport ACLs.
In addition, the following flows are added.
• A priority 34000 logical flow is added for each logical port which has
DHCPv4 options defined to allow the DHCPv4 reply packet and which has DHCPv6
options defined to allow the DHCPv6 reply packet from the Ingress Table 15:
DHCP responses.
• A priority 34000 logical flow is added for each logical switch datapath
configured with DNS records with the match udp.dst = 53 to allow the DNS
reply packet from the Ingress Table 17: DNS responses.
• A priority 34000 logical flow is added for each logical switch datapath with
the match eth.src = E to allow the service monitor request packet generated
by ovn-controller with the action next, where E is the service monitor mac
defined in the options:svc_monitor_mac colum of NB_Global table.
Egress Table 5: to-lport QoS Marking
This is similar to ingress table QoS marking except they apply to to-lport QoS rules.
Egress Table 6: to-lport QoS Meter
This is similar to ingress table QoS meter except they apply to to-lport QoS rules.
Egress Table 7: Stateful
This is similar to ingress table Stateful except that there are no rules added for load
balancing new connections.
Egress Table 8: Egress Port Security - IP
This is similar to the port security logic in table Ingress Port Security - IP except that
outport, eth.dst, ip4.dst and ip6.dst are checked instead of inport, eth.src, ip4.src and
ip6.src
Egress Table 9: Egress Port Security - L2
This is similar to the ingress port security logic in ingress table Admission Control and
Ingress Port Security - L2, but with important differences. Most obviously, outport and
eth.dst are checked instead of inport and eth.src. Second, packets directed to broadcast
or multicast eth.dst are always accepted instead of being subject to the port security
rules; this is implemented through a priority-100 flow that matches on eth.mcast with
action output;. Moreover, to ensure that even broadcast and multicast packets are not
delivered to disabled logical ports, a priority-150 flow for each disabled logical outport
overrides the priority-100 flow with a drop; action. Finally if egress qos has been
enabled on a localnet port, the outgoing queue id is set through set_queue action. Please
remember to mark the corresponding physical interface with ovn-egress-iface set to true in
external_ids
Logical Router Datapaths
Logical router datapaths will only exist for Logical_Router rows in the OVN_Northbound
database that do not have enabled set to false
Ingress Table 0: L2 Admission Control
This table drops packets that the router shouldn’t see at all based on their Ethernet
headers. It contains the following flows:
• Priority-100 flows to drop packets with VLAN tags or multicast Ethernet
source addresses.
• For each enabled router port P with Ethernet address E, a priority-50 flow
that matches inport == P && (eth.mcast || eth.dst == E), with action next;.
For the gateway port on a distributed logical router (where one of the
logical router ports specifies a redirect-chassis), the above flow matching
eth.dst == E is only programmed on the gateway port instance on the
redirect-chassis.
• For each dnat_and_snat NAT rule on a distributed router that specifies an
external Ethernet address E, a priority-50 flow that matches inport == GW &&
eth.dst == E, where GW is the logical router gateway port, with action
next;.
This flow is only programmed on the gateway port instance on the chassis
where the logical_port specified in the NAT rule resides.
Other packets are implicitly dropped.
Ingress Table 1: Neighbor lookup
For ARP and IPv6 Neighbor Discovery packets, this table looks into the MAC_Binding records
to determine if OVN needs to learn the mac bindings. Following flows are added:
• For each router port P that owns IP address A, which belongs to subnet S
with prefix length L, a priority-100 flow is added which matches inport == P
&& arp.spa == S/L && arp.op == 1 (ARP request) with the following actions:
reg9[4] = lookup_arp(inport, arp.spa, arp.sha);
next;
If the logical router port P is a distributed gateway router port,
additional match is_chassis_resident(cr-P) is added so that the resident
gateway chassis handles the neighbor lookup.
• A priority-100 flow which matches on ARP reply packets and applies the
actions:
reg9[4] = lookup_arp(inport, arp.spa, arp.sha);
next;
• A priority-100 flow which matches on IPv6 Neighbor Discovery advertisement
packet and applies the actions:
reg9[4] = lookup_nd(inport, nd.target, nd.tll);
next;
• A priority-100 flow which matches on IPv6 Neighbor Discovery solicitation
packet and applies the actions:
reg9[4] = lookup_nd(inport, ip6.src, nd.sll);
next;
• A priority-0 fallback flow that matches all packets and applies the action
reg9[5] = 1; next; advancing the packet to the next table.
Ingress Table 2: Neighbor learning
This table adds flows to learn the mac bindings from the ARP and IPv6 Neighbor
Solicitation/Advertisement packets if ARP/ND lookup failed in the previous table.
reg9[4] will be 1 if the lookup_arp/lookup_nd in the previous table was successful.
reg9[5] will be 1 if there was no need to do the lookup.
• A priority-100 flow with the match reg9[4] == 1 || reg9[5] == 1 and advances
the packet to the next table as there is no need to learn the neighbor.
• A priority-90 flow with the match arp and applies the action put_arp(inport,
arp.spa, arp.sha); next;
• A priority-90 flow with the match nd_na and applies the action
put_nd(inport, nd.target, nd.tll); next;
• A priority-90 flow with the match nd_ns and applies the action
put_nd(inport, ip6.src, nd.sll); next;
Ingress Table 3: IP Input
This table is the core of the logical router datapath functionality. It contains the
following flows to implement very basic IP host functionality.
• For each NAT entry of a distributed logical router (with distributed gateway
router port) of type snat, a priorirty-120 flow with the match inport == P
&& ip4.src == A advances the packet to the next pipeline, where P is the
distributed logical router port and A is the external_ip set in the NAT
entry. If A is an IPv6 address, then ip6.src is used for the match.
The above flow is required to handle the routing of the East/west NAT
traffic.
• L3 admission control: A priority-100 flow drops packets that match any of
the following:
• ip4.src[28..31] == 0xe (multicast source)
• ip4.src == 255.255.255.255 (broadcast source)
• ip4.src == 127.0.0.0/8 || ip4.dst == 127.0.0.0/8 (localhost source or
destination)
• ip4.src == 0.0.0.0/8 || ip4.dst == 0.0.0.0/8 (zero network source or
destination)
• ip4.src or ip6.src is any IP address owned by the router, unless the
packet was recirculated due to egress loopback as indicated by
REGBIT_EGRESS_LOOPBACK.
• ip4.src is the broadcast address of any IP network known to the
router.
• ICMP echo reply. These flows reply to ICMP echo requests received for the
router’s IP address. Let A be an IP address owned by a router port. Then,
for each A that is an IPv4 address, a priority-90 flow matches on ip4.dst ==
A and icmp4.type == 8 && icmp4.code == 0 (ICMP echo request). For each A
that is an IPv6 address, a priority-90 flow matches on ip6.dst == A and
icmp6.type == 128 && icmp6.code == 0 (ICMPv6 echo request). The port of the
router that receives the echo request does not matter. Also, the ip.ttl of
the echo request packet is not checked, so it complies with RFC 1812,
section 4.2.2.9. Flows for ICMPv4 echo requests use the following actions:
ip4.dst <-> ip4.src;
ip.ttl = 255;
icmp4.type = 0;
flags.loopback = 1;
next;
Flows for ICMPv6 echo requests use the following actions:
ip6.dst <-> ip6.src;
ip.ttl = 255;
icmp6.type = 129;
flags.loopback = 1;
next;
• Reply to ARP requests.
These flows reply to ARP requests for the router’s own IP address. The ARP
requests are handled only if the requestor’s IP belongs to the same subnets
of the logical router port. For each router port P that owns IP address A,
which belongs to subnet S with prefix length L, and Ethernet address E, a
priority-90 flow matches inport == P && arp.spa == S/L && arp.op == 1 &&
arp.tpa == A (ARP request) with the following actions:
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = P;
flags.loopback = 1;
output;
For the gateway port on a distributed logical router (where one of the
logical router ports specifies a redirect-chassis), the above flows are only
programmed on the gateway port instance on the redirect-chassis. This
behavior avoids generation of multiple ARP responses from different chassis,
and allows upstream MAC learning to point to the redirect-chassis.
For the logical router port with the option reside-on-redirect-chassis set
(which is centralized), the above flows are only programmed on the gateway
port instance on the redirect-chassis (if the logical router has a
distributed gateway port). This behavior avoids generation of multiple ARP
responses from different chassis, and allows upstream MAC learning to point
to the redirect-chassis.
• Reply to IPv6 Neighbor Solicitations. These flows reply to Neighbor
Solicitation requests for the router’s own IPv6 address and populate the
logical router’s mac binding table.
For each router port P that owns IPv6 address A, solicited node address S,
and Ethernet address E, a priority-90 flow matches inport == P && nd_ns &&
ip6.dst == {A, E} && nd.target == A with the following actions:
nd_na_router {
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
For the gateway port on a distributed logical router (where one of the
logical router ports specifies a redirect-chassis), the above flows replying
to IPv6 Neighbor Solicitations are only programmed on the gateway port
instance on the redirect-chassis. This behavior avoids generation of
multiple replies from different chassis, and allows upstream MAC learning to
point to the redirect-chassis.
• These flows reply to ARP requests or IPv6 neighbor solicitation for the
virtual IP addresses configured in the router for DNAT or load balancing.
IPv4: For a configured DNAT IP address or a load balancer IPv4 VIP A, for
each router port P with Ethernet address E, a priority-90 flow matches
inport == P && arp.op == 1 && arp.tpa == A (ARP request) with the following
actions:
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = P;
flags.loopback = 1;
output;
If the router port P is a distributed gateway router port, then the
is_chassis_resident(P) is also added in the match condition for the load
balancer IPv4 VIP A.
IPv6: For a configured DNAT IP address or a load balancer IPv6 VIP A,
solicited node address S, for each router port P with Ethernet address E, a
priority-90 flow matches inport == P && nd_ns && ip6.dst == {A, S} &&
nd.target == A with the following actions:
eth.dst = eth.src;
nd_na {
eth.src = E;
nd.tll = E;
ip6.src = A;
nd.target = A;
outport = P;
flags.loopback = 1;
output;
}
If the router port P is a distributed gateway router port, then the
is_chassis_resident(P) is also added in the match condition for the load
balancer IPv6 VIP A.
For the gateway port on a distributed logical router with NAT (where one of
the logical router ports specifies a redirect-chassis):
• If the corresponding NAT rule cannot be handled in a distributed
manner, then this flow is only programmed on the gateway port
instance on the redirect-chassis. This behavior avoids generation of
multiple ARP responses from different chassis, and allows upstream
MAC learning to point to the redirect-chassis.
• If the corresponding NAT rule can be handled in a distributed manner,
then this flow is only programmed on the gateway port instance where
the logical_port specified in the NAT rule resides.
Some of the actions are different for this case, using the
external_mac specified in the NAT rule rather than the gateway port’s
Ethernet address E:
eth.src = external_mac;
arp.sha = external_mac;
or in the case of IPv6 neighbor solicition:
eth.src = external_mac;
nd.tll = external_mac;
This behavior avoids generation of multiple ARP responses from
different chassis, and allows upstream MAC learning to point to the
correct chassis.
• Priority-85 flows which drops the ARP and IPv6 Neighbor Discovery packets.
• A priority-84 flow explicitly allows IPv6 multicast traffic that is supposed
to reach the router pipeline (i.e., router solicitation and router
advertisement packets).
• A priority-83 flow explicitly drops IPv6 multicast traffic that is destined
to reserved multicast groups.
• A priority-82 flow allows IP multicast traffic if
options:mcast_relay=’true’, otherwise drops it.
• UDP port unreachable. Priority-80 flows generate ICMP port unreachable
messages in reply to UDP datagrams directed to the router’s IP address,
except in the special case of gateways, which accept traffic directed to a
router IP for load balancing and NAT purposes.
These flows should not match IP fragments with nonzero offset.
• TCP reset. Priority-80 flows generate TCP reset messages in reply to TCP
datagrams directed to the router’s IP address, except in the special case of
gateways, which accept traffic directed to a router IP for load balancing
and NAT purposes.
These flows should not match IP fragments with nonzero offset.
• Protocol or address unreachable. Priority-70 flows generate ICMP protocol or
address unreachable messages for IPv4 and IPv6 respectively in reply to
packets directed to the router’s IP address on IP protocols other than UDP,
TCP, and ICMP, except in the special case of gateways, which accept traffic
directed to a router IP for load balancing purposes.
These flows should not match IP fragments with nonzero offset.
• Drop other IP traffic to this router. These flows drop any other traffic
destined to an IP address of this router that is not already handled by one
of the flows above, which amounts to ICMP (other than echo requests) and
fragments with nonzero offsets. For each IP address A owned by the router, a
priority-60 flow matches ip4.dst == A or ip6.dst == A and drops the traffic.
An exception is made and the above flow is not added if the router port’s
own IP address is used to SNAT packets passing through that router.
The flows above handle all of the traffic that might be directed to the router itself. The
following flows (with lower priorities) handle the remaining traffic, potentially for
forwarding:
• Drop Ethernet local broadcast. A priority-50 flow with match eth.bcast drops
traffic destined to the local Ethernet broadcast address. By definition this
traffic should not be forwarded.
• ICMP time exceeded. For each router port P, whose IP address is A, a
priority-40 flow with match inport == P && ip.ttl == {0, 1} &&
!ip.later_frag matches packets whose TTL has expired, with the following
actions to send an ICMP time exceeded reply for IPv4 and IPv6 respectively:
icmp4 {
icmp4.type = 11; /* Time exceeded. */
icmp4.code = 0; /* TTL exceeded in transit. */
ip4.dst = ip4.src;
ip4.src = A;
ip.ttl = 255;
next;
};
icmp6 {
icmp6.type = 3; /* Time exceeded. */
icmp6.code = 0; /* TTL exceeded in transit. */
ip6.dst = ip6.src;
ip6.src = A;
ip.ttl = 255;
next;
};
• TTL discard. A priority-30 flow with match ip.ttl == {0, 1} and actions
drop; drops other packets whose TTL has expired, that should not receive a
ICMP error reply (i.e. fragments with nonzero offset).
• Next table. A priority-0 flows match all packets that aren’t already handled
and uses actions next; to feed them to the next table.
Ingress Table 4: DEFRAG
This is to send packets to connection tracker for tracking and defragmentation. It
contains a priority-0 flow that simply moves traffic to the next table. If load balancing
rules with virtual IP addresses (and ports) are configured in OVN_Northbound database for
a Gateway router, a priority-100 flow is added for each configured virtual IP address VIP.
For IPv4 VIPs the flow matches ip && ip4.dst == VIP. For IPv6 VIPs, the flow matches ip &&
ip6.dst == VIP. The flow uses the action ct_next; to send IP packets to the connection
tracker for packet de-fragmentation and tracking before sending it to the next table.
Ingress Table 5: UNSNAT
This is for already established connections’ reverse traffic. i.e., SNAT has already been
done in egress pipeline and now the packet has entered the ingress pipeline as part of a
reply. It is unSNATted here.
Ingress Table 5: UNSNAT on Gateway and Distributed Routers
• If the Router (Gateway or Distributed) is configured with load balancers,
then below lflows are added:
For each IPv4 address A defined as load balancer VIP with the protocol P
(and the protocol port T if defined) is also present as an external_ip in
the NAT table, a priority-120 logical flow is added with the match ip4 &&
ip4.dst == A && P with the action next; to advance the packet to the next
table. If the load balancer has protocol port B defined, then the match also
has P.dst == B.
The above flows are also added for IPv6 load balancers.
Ingress Table 5: UNSNAT on Gateway Routers
• If the Gateway router has been configured to force SNAT any previously
DNATted packets to B, a priority-110 flow matches ip && ip4.dst == B or ip
&& ip6.dst == B with an action ct_snat; .
If the Gateway router has been configured to force SNAT any previously load-
balanced packets to B, a priority-100 flow matches ip && ip4.dst == B or ip
&& ip6.dst == B with an action ct_snat; .
For each NAT configuration in the OVN Northbound database, that asks to
change the source IP address of a packet from A to B, a priority-90 flow
matches ip && ip4.dst == B or ip && ip6.dst == B with an action ct_snat; .
If the NAT rule is of type dnat_and_snat and has stateless=true in the
options, then the action would be ip4/6.dst= (B).
A priority-0 logical flow with match 1 has actions next;.
Ingress Table 5: UNSNAT on Distributed Routers
• For each configuration in the OVN Northbound database, that asks to change
the source IP address of a packet from A to B, a priority-100 flow matches
ip && ip4.dst == B && inport == GW or ip && ip6.dst == B && inport == GW
where GW is the logical router gateway port, with an action ct_snat;. If the
NAT rule is of type dnat_and_snat and has stateless=true in the options,
then the action would be ip4/6.dst= (B).
If the NAT rule cannot be handled in a distributed manner, then the
priority-100 flow above is only programmed on the redirect-chassis.
A priority-0 logical flow with match 1 has actions next;.
Ingress Table 6: DNAT
Packets enter the pipeline with destination IP address that needs to be DNATted from a
virtual IP address to a real IP address. Packets in the reverse direction needs to be
unDNATed.
Ingress Table 6: Load balancing DNAT rules
Following load balancing DNAT flows are added for Gateway router or Router with gateway
port. These flows are programmed only on the redirect-chassis. These flows do not get
programmed for load balancers with IPv6 VIPs.
• If controller_event has been enabled for all the configured load balancing
rules for a Gateway router or Router with gateway port in OVN_Northbound
database that does not have configured backends, a priority-130 flow is
added to trigger ovn-controller events whenever the chassis receives a
packet for that particular VIP. If event-elb meter has been previously
created, it will be associated to the empty_lb logical flow
• For all the configured load balancing rules for a Gateway router or Router
with gateway port in OVN_Northbound database that includes a L4 port PORT of
protocol P and IPv4 or IPv6 address VIP, a priority-120 flow that matches on
ct.new && ip && ip4.dst == VIP && P && P.dst == PORT
(ip6.dst == VIP in the IPv6 case) with an action of ct_lb(args), where args
contains comma separated IPv4 or IPv6 addresses (and optional port numbers)
to load balance to. If the router is configured to force SNAT any load-
balanced packets, the above action will be replaced by
flags.force_snat_for_lb = 1; ct_lb(args);. If health check is enabled, then
args will only contain those endpoints whose service monitor status entry in
OVN_Southbound db is either online or empty.
• For all the configured load balancing rules for a router in OVN_Northbound
database that includes a L4 port PORT of protocol P and IPv4 or IPv6 address
VIP, a priority-120 flow that matches on ct.est && ip && ip4.dst == VIP && P
&& P.dst == PORT
(ip6.dst == VIP in the IPv6 case) with an action of ct_dnat;. If the router
is configured to force SNAT any load-balanced packets, the above action will
be replaced by flags.force_snat_for_lb = 1; ct_dnat;.
• For all the configured load balancing rules for a router in OVN_Northbound
database that includes just an IP address VIP to match on, a priority-110
flow that matches on ct.new && ip && ip4.dst == VIP (ip6.dst == VIP in the
IPv6 case) with an action of ct_lb(args), where args contains comma
separated IPv4 or IPv6 addresses. If the router is configured to force SNAT
any load-balanced packets, the above action will be replaced by
flags.force_snat_for_lb = 1; ct_lb(args);.
• For all the configured load balancing rules for a router in OVN_Northbound
database that includes just an IP address VIP to match on, a priority-110
flow that matches on ct.est && ip && ip4.dst == VIP (or ip6.dst == VIP) with
an action of ct_dnat;. If the router is configured to force SNAT any load-
balanced packets, the above action will be replaced by
flags.force_snat_for_lb = 1; ct_dnat;.
Ingress Table 6: DNAT on Gateway Routers
• For each configuration in the OVN Northbound database, that asks to change
the destination IP address of a packet from A to B, a priority-100 flow
matches ip && ip4.dst == A or ip && ip6.dst == A with an action
flags.loopback = 1; ct_dnat(B);. If the Gateway router is configured to
force SNAT any DNATed packet, the above action will be replaced by
flags.force_snat_for_dnat = 1; flags.loopback = 1; ct_dnat(B);. If the NAT
rule is of type dnat_and_snat and has stateless=true in the options, then
the action would be ip4/6.dst= (B).
• For all IP packets of a Gateway router, a priority-50 flow with an action
flags.loopback = 1; ct_dnat;.
• A priority-0 logical flow with match 1 has actions next;.
Ingress Table 6: DNAT on Distributed Routers
On distributed routers, the DNAT table only handles packets with destination IP address
that needs to be DNATted from a virtual IP address to a real IP address. The unDNAT
processing in the reverse direction is handled in a separate table in the egress pipeline.
• For each configuration in the OVN Northbound database, that asks to change
the destination IP address of a packet from A to B, a priority-100 flow
matches ip && ip4.dst == B && inport == GW, where GW is the logical router
gateway port, with an action ct_dnat(B);. The match will include ip6.dst ==
B in the IPv6 case. If the NAT rule is of type dnat_and_snat and has
stateless=true in the options, then the action would be ip4/6.dst=(B).
If the NAT rule cannot be handled in a distributed manner, then the
priority-100 flow above is only programmed on the redirect-chassis.
A priority-0 logical flow with match 1 has actions next;.
Ingress Table 7: IPv6 ND RA option processing
• A priority-50 logical flow is added for each logical router port configured
with IPv6 ND RA options which matches IPv6 ND Router Solicitation packet and
applies the action put_nd_ra_opts and advances the packet to the next table.
reg0[5] = put_nd_ra_opts(options);next;
For a valid IPv6 ND RS packet, this transforms the packet into an IPv6 ND RA
reply and sets the RA options to the packet and stores 1 into reg0[5]. For
other kinds of packets, it just stores 0 into reg0[5]. Either way, it
continues to the next table.
• A priority-0 logical flow with match 1 has actions next;.
Ingress Table 8: IPv6 ND RA responder
This table implements IPv6 ND RA responder for the IPv6 ND RA replies generated by the
previous table.
• A priority-50 logical flow is added for each logical router port configured
with IPv6 ND RA options which matches IPv6 ND RA packets and reg0[5] == 1
and responds back to the inport after applying these actions. If reg0[5] is
set to 1, it means that the action put_nd_ra_opts was successful.
eth.dst = eth.src;
eth.src = E;
ip6.dst = ip6.src;
ip6.src = I;
outport = P;
flags.loopback = 1;
output;
where E is the MAC address and I is the IPv6 link local address of the
logical router port.
(This terminates packet processing in ingress pipeline; the packet does not
go to the next ingress table.)
• A priority-0 logical flow with match 1 has actions next;.
Ingress Table 9: IP Routing
A packet that arrives at this table is an IP packet that should be routed to the address
in ip4.dst or ip6.dst. This table implements IP routing, setting reg0 (or xxreg0 for IPv6)
to the next-hop IP address (leaving ip4.dst or ip6.dst, the packet’s final destination,
unchanged) and advances to the next table for ARP resolution. It also sets reg1 (or
xxreg1) to the IP address owned by the selected router port (ingress table ARP Request
will generate an ARP request, if needed, with reg0 as the target protocol address and reg1
as the source protocol address).
For ECMP routes, i.e. multiple static routes with same policy and prefix but different
nexthops, the above actions are deferred to next table. This table, instead, is
responsible for determine the ECMP group id and select a member id within the group based
on 5-tuple hashing. It stores group id in reg8[0..15] and member id in reg8[16..31].
This table contains the following logical flows:
• Priority-550 flow that drops IPv6 Router Solicitation/Advertisement packets
that were not processed in previous tables.
• Priority-500 flows that match IP multicast traffic destined to groups
registered on any of the attached switches and sets outport to the
associated multicast group that will eventually flood the traffic to all
interested attached logical switches. The flows also decrement TTL.
• Priority-450 flow that matches unregistered IP multicast traffic and sets
outport to the MC_STATIC multicast group, which ovn-northd populates with
the logical ports that have options :mcast_flood=’true’. If no router ports
are configured to flood multicast traffic the packets are dropped.
• IPv4 routing table. For each route to IPv4 network N with netmask M, on
router port P with IP address A and Ethernet address E, a logical flow with
match ip4.dst == N/M, whose priority is the number of 1-bits in M, has the
following actions:
ip.ttl--;
reg8[0..15] = 0;
reg0 = G;
reg1 = A;
eth.src = E;
outport = P;
flags.loopback = 1;
next;
(Ingress table 1 already verified that ip.ttl--; will not yield a TTL
exceeded error.)
If the route has a gateway, G is the gateway IP address. Instead, if the
route is from a configured static route, G is the next hop IP address. Else
it is ip4.dst.
• IPv6 routing table. For each route to IPv6 network N with netmask M, on
router port P with IP address A and Ethernet address E, a logical flow with
match in CIDR notation ip6.dst == N/M, whose priority is the integer value
of M, has the following actions:
ip.ttl--;
reg8[0..15] = 0;
xxreg0 = G;
xxreg1 = A;
eth.src = E;
outport = P;
flags.loopback = 1;
next;
(Ingress table 1 already verified that ip.ttl--; will not yield a TTL
exceeded error.)
If the route has a gateway, G is the gateway IP address. Instead, if the
route is from a configured static route, G is the next hop IP address. Else
it is ip6.dst.
If the address A is in the link-local scope, the route will be limited to
sending on the ingress port.
• For ECMP routes, they are grouped by policy and prefix. An unique id (non-
zero) is assigned to each group, and each member is also assigned an unique
id (non-zero) within each group.
For each IPv4/IPv6 ECMP group with group id GID and member ids MID1, MID2,
..., a logical flow with match in CIDR notation ip4.dst == N/M, or ip6.dst
== N/M, whose priority is the integer value of M, has the following actions:
ip.ttl--;
flags.loopback = 1;
reg8[0..15] = GID;
select(reg8[16..31], MID1, MID2, ...);
Ingress Table 10: IP_ROUTING_ECMP
This table implements the second part of IP routing for ECMP routes following the previous
table. If a packet matched a ECMP group in the previous table, this table matches the
group id and member id stored from the previous table, setting reg0 (or xxreg0 for IPv6)
to the next-hop IP address (leaving ip4.dst or ip6.dst, the packet’s final destination,
unchanged) and advances to the next table for ARP resolution. It also sets reg1 (or
xxreg1) to the IP address owned by the selected router port (ingress table ARP Request
will generate an ARP request, if needed, with reg0 as the target protocol address and reg1
as the source protocol address).
This table contains the following logical flows:
• A priority-150 flow that matches reg8[0..15] == 0 with action next; directly
bypasses packets of non-ECMP routes.
• For each member with ID MID in each ECMP group with ID GID, a priority-100
flow with match reg8[0..15] == GID && reg8[16..31] == MID has following
actions:
[xx]reg0 = G;
[xx]reg1 = A;
eth.src = E;
outport = P;
Ingress Table 12: ARP/ND Resolution
Any packet that reaches this table is an IP packet whose next-hop IPv4 address is in reg0
or IPv6 address is in xxreg0. (ip4.dst or ip6.dst contains the final destination.) This
table resolves the IP address in reg0 (or xxreg0) into an output port in outport and an
Ethernet address in eth.dst, using the following flows:
• A priority-500 flow that matches IP multicast traffic that was allowed in
the routing pipeline. For this kind of traffic the outport was already set
so the flow just advances to the next table.
• Static MAC bindings. MAC bindings can be known statically based on data in
the OVN_Northbound database. For router ports connected to logical switches,
MAC bindings can be known statically from the addresses column in the
Logical_Switch_Port table. For router ports connected to other logical
routers, MAC bindings can be known statically from the mac and networks
column in the Logical_Router_Port table.
For each IPv4 address A whose host is known to have Ethernet address E on
router port P, a priority-100 flow with match outport === P && reg0 == A has
actions eth.dst = E; next;.
For each virtual ip A configured on a logical port of type virtual and its
virtual parent set in its corresponding Port_Binding record and the virtual
parent with the Ethernet address E and the virtual ip is reachable via the
router port P, a priority-100 flow with match outport === P && reg0 == A has
actions eth.dst = E; next;.
For each virtual ip A configured on a logical port of type virtual and its
virtual parent not set in its corresponding Port_Binding record and the
virtual ip A is reachable via the router port P, a priority-100 flow with
match outport === P && reg0 == A has actions eth.dst = 00:00:00:00:00:00;
next;. This flow is added so that the ARP is always resolved for the virtual
ip A by generating ARP request and not consulting the MAC_Binding table as
it can have incorrect value for the virtual ip A.
For each IPv6 address A whose host is known to have Ethernet address E on
router port P, a priority-100 flow with match outport === P && xxreg0 == A
has actions eth.dst = E; next;.
For each logical router port with an IPv4 address A and a mac address of E
that is reachable via a different logical router port P, a priority-100 flow
with match outport === P && reg0 == A has actions eth.dst = E; next;.
For each logical router port with an IPv6 address A and a mac address of E
that is reachable via a different logical router port P, a priority-100 flow
with match outport === P && xxreg0 == A has actions eth.dst = E; next;.
• Static MAC bindings from NAT entries. MAC bindings can also be known for the
entries in the NAT table. Below flows are programmed for distributed logical
routers i.e with a distributed router port.
For each row in the NAT table with IPv4 address A in the external_ip column
of NAT table, a priority-100 flow with the match outport === P && reg0 == A
has actions eth.dst = E; next;, where P is the distributed logical router
port, E is the Ethernet address if set in the external_mac column of NAT
table for of type dnat_and_snat, otherwise the Ethernet address of the
distributed logical router port.
For IPv6 NAT entries, same flows are added, but using the register xxreg0
for the match.
• Dynamic MAC bindings. These flows resolve MAC-to-IP bindings that have
become known dynamically through ARP or neighbor discovery. (The ingress
table ARP Request will issue an ARP or neighbor solicitation request for
cases where the binding is not yet known.)
A priority-0 logical flow with match ip4 has actions get_arp(outport, reg0);
next;.
A priority-0 logical flow with match ip6 has actions get_nd(outport,
xxreg0); next;.
• For logical router port with redirect-chassis and redirect-type being set as
bridged, a priority-50 flow will match outport == "ROUTER_PORT" and
!is_chassis_resident ("cr-ROUTER_PORT") has actions eth.dst = E; next;,
where E is the ethernet address of the logical router port.
Ingress Table 13: Check packet length
For distributed logical routers with distributed gateway port configured with
options:gateway_mtu to a valid integer value, this table adds a priority-50 logical flow
with the match ip4 && outport == GW_PORT where GW_PORT is the distributed gateway router
port and applies the action check_pkt_larger and advances the packet to the next table.
REGBIT_PKT_LARGER = check_pkt_larger(L); next;
where L is the packet length to check for. If the packet is larger than L, it stores 1 in
the register bit REGBIT_PKT_LARGER. The value of L is taken from options:gateway_mtu
column of Logical_Router_Port row.
This table adds one priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 14: Handle larger packets
For distributed logical routers with distributed gateway port configured with
options:gateway_mtu to a valid integer value, this table adds the following priority-50
logical flow for each logical router port with the match ip4 && inport == LRP && outport
== GW_PORT && REGBIT_PKT_LARGER, where LRP is the logical router port and GW_PORT is the
distributed gateway router port and applies the following action
icmp4 {
icmp4.type = 3; /* Destination Unreachable. */
icmp4.code = 4; /* Frag Needed and DF was Set. */
icmp4.frag_mtu = M;
eth.dst = E;
ip4.dst = ip4.src;
ip4.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
next(pipeline=ingress, table=0);
};
• Where M is the (fragment MTU - 58) whose value is taken from
options:gateway_mtu column of Logical_Router_Port row.
• E is the Ethernet address of the logical router port.
• I is the IPv4 address of the logical router port.
This table adds one priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 15: Gateway Redirect
For distributed logical routers where one of the logical router ports specifies a
redirect-chassis, this table redirects certain packets to the distributed gateway port
instance on the redirect-chassis. This table has the following flows:
• A priority-150 logical flow with match outport == GW && eth.dst ==
00:00:00:00:00:00 has actions outport = CR; next;, where GW is the logical
router distributed gateway port and CR is the chassisredirect port
representing the instance of the logical router distributed gateway port on
the redirect-chassis.
• For each NAT rule in the OVN Northbound database that can be handled in a
distributed manner, a priority-100 logical flow with match ip4.src == B &&
outport == GW, where GW is the logical router distributed gateway port, with
actions next;.
• A priority-50 logical flow with match outport == GW has actions outport =
CR; next;, where GW is the logical router distributed gateway port and CR is
the chassisredirect port representing the instance of the logical router
distributed gateway port on the redirect-chassis.
• A priority-0 logical flow with match 1 has actions next;.
Ingress Table 16: ARP Request
In the common case where the Ethernet destination has been resolved, this table outputs
the packet. Otherwise, it composes and sends an ARP or IPv6 Neighbor Solicitation request.
It holds the following flows:
• Unknown MAC address. A priority-100 flow for IPv4 packets with match eth.dst
== 00:00:00:00:00:00 has the following actions:
arp {
eth.dst = ff:ff:ff:ff:ff:ff;
arp.spa = reg1;
arp.tpa = reg0;
arp.op = 1; /* ARP request. */
output;
};
Unknown MAC address. For each IPv6 static route associated with the router
with the nexthop IP: G, a priority-200 flow for IPv6 packets with match
eth.dst == 00:00:00:00:00:00 && xxreg0 == G with the following actions is
added:
nd_ns {
eth.dst = E;
ip6.dst = I
nd.target = G;
output;
};
Where E is the multicast mac derived from the Gateway IP, I is the
solicited-node multicast address corresponding to the target address G.
Unknown MAC address. A priority-100 flow for IPv6 packets with match eth.dst
== 00:00:00:00:00:00 has the following actions:
nd_ns {
nd.target = xxreg0;
output;
};
(Ingress table IP Routing initialized reg1 with the IP address owned by
outport and (xx)reg0 with the next-hop IP address)
The IP packet that triggers the ARP/IPv6 NS request is dropped.
• Known MAC address. A priority-0 flow with match 1 has actions output;.
Egress Table 0: UNDNAT
This is for already established connections’ reverse traffic. i.e., DNAT has already been
done in ingress pipeline and now the packet has entered the egress pipeline as part of a
reply. For NAT on a distributed router, it is unDNATted here. For Gateway routers, the
unDNAT processing is carried out in the ingress DNAT table.
• For all the configured load balancing rules for a router with gateway port
in OVN_Northbound database that includes an IPv4 address VIP, for every
backend IPv4 address B defined for the VIP a priority-120 flow is programmed
on redirect-chassis that matches ip && ip4.src == B && outport == GW, where
GW is the logical router gateway port with an action ct_dnat;. If the
backend IPv4 address B is also configured with L4 port PORT of protocol P,
then the match also includes P.src == PORT. These flows are not added for
load balancers with IPv6 VIPs.
If the router is configured to force SNAT any load-balanced packets, above
action will be replaced by flags.force_snat_for_lb = 1; ct_dnat;.
• For each configuration in the OVN Northbound database that asks to change
the destination IP address of a packet from an IP address of A to B, a
priority-100 flow matches ip && ip4.src == B && outport == GW, where GW is
the logical router gateway port, with an action ct_dnat;. If the NAT rule is
of type dnat_and_snat and has stateless=true in the options, then the action
would be ip4/6.src= (B).
If the NAT rule cannot be handled in a distributed manner, then the
priority-100 flow above is only programmed on the redirect-chassis.
If the NAT rule can be handled in a distributed manner, then there is an
additional action eth.src = EA;, where EA is the ethernet address associated
with the IP address A in the NAT rule. This allows upstream MAC learning to
point to the correct chassis.
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 1: SNAT
Packets that are configured to be SNATed get their source IP address changed based on the
configuration in the OVN Northbound database.
• A priority-120 flow to advance the IPv6 Neighbor solicitation packet to next
table to skip SNAT. In the case where ovn-controller injects an IPv6
Neighbor Solicitation packet (for nd_ns action) we don’t want the packet to
go throught conntrack.
Egress Table 1: SNAT on Gateway Routers
• If the Gateway router in the OVN Northbound database has been configured to
force SNAT a packet (that has been previously DNATted) to B, a priority-100
flow matches flags.force_snat_for_dnat == 1 && ip with an action
ct_snat(B);.
If the Gateway router in the OVN Northbound database has been configured to
force SNAT a packet (that has been previously load-balanced) to B, a
priority-100 flow matches flags.force_snat_for_lb == 1 && ip with an action
ct_snat(B);.
For each configuration in the OVN Northbound database, that asks to change
the source IP address of a packet from an IP address of A or to change the
source IP address of a packet that belongs to network A to B, a flow matches
ip && ip4.src == A with an action ct_snat(B);. The priority of the flow is
calculated based on the mask of A, with matches having larger masks getting
higher priorities. If the NAT rule is of type dnat_and_snat and has
stateless=true in the options, then the action would be ip4/6.src= (B).
A priority-0 logical flow with match 1 has actions next;.
Egress Table 1: SNAT on Distributed Routers
• For each configuration in the OVN Northbound database, that asks to change
the source IP address of a packet from an IP address of A or to change the
source IP address of a packet that belongs to network A to B, a flow matches
ip && ip4.src == A && outport == GW, where GW is the logical router gateway
port, with an action ct_snat(B);. The priority of the flow is calculated
based on the mask of A, with matches having larger masks getting higher
priorities. If the NAT rule is of type dnat_and_snat and has stateless=true
in the options, then the action would be ip4/6.src= (B).
If the NAT rule cannot be handled in a distributed manner, then the flow
above is only programmed on the redirect-chassis increasing flow priority by
128 in order to be run first
If the NAT rule can be handled in a distributed manner, then there is an
additional action eth.src = EA;, where EA is the ethernet address associated
with the IP address A in the NAT rule. This allows upstream MAC learning to
point to the correct chassis.
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 2: Egress Loopback
For distributed logical routers where one of the logical router ports specifies a
redirect-chassis.
While UNDNAT and SNAT processing have already occurred by this point, this traffic needs
to be forced through egress loopback on this distributed gateway port instance, in order
for UNSNAT and DNAT processing to be applied, and also for IP routing and ARP resolution
after all of the NAT processing, so that the packet can be forwarded to the destination.
This table has the following flows:
• For each NAT rule in the OVN Northbound database on a distributed router, a
priority-100 logical flow with match ip4.dst == E && outport == GW &&
is_chassis_resident(P), where E is the external IP address specified in the
NAT rule, GW is the logical router distributed gateway port. For
dnat_and_snat NAT rule, P is the logical port specified in the NAT rule. If
logical_port column of NAT table is NOT set, then P is the chassisredirect
port of GW with the following actions:
clone {
ct_clear;
inport = outport;
outport = "";
flags = 0;
flags.loopback = 1;
reg0 = 0;
reg1 = 0;
...
reg9 = 0;
REGBIT_EGRESS_LOOPBACK = 1;
next(pipeline=ingress, table=0);
};
flags.loopback is set since in_port is unchanged and the packet may return
back to that port after NAT processing. REGBIT_EGRESS_LOOPBACK is set to
indicate that egress loopback has occurred, in order to skip the source IP
address check against the router address.
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 3: Delivery
Packets that reach this table are ready for delivery. It contains:
• Priority-110 logical flows that match IP multicast packets on each enabled
logical router port and modify the Ethernet source address of the packets to
the Ethernet address of the port and then execute action output;.
• Priority-100 logical flows that match packets on each enabled logical router
port, with action output;.