Provided by: ovn-common_23.09.0-1ubuntu1_amd64 
NAME
ovn-northd and ovn-northd-ddlog - 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.
ovn-northd is implemented in C. ovn-northd-ddlog is a compatible implementation written in
DDlog, a language for incremental database processing. This documentation applies to both
implementations, with differences indicated where relevant.
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.
--ddlog-record=file
This option is for ovn-north-ddlog only. It causes the daemon to record the initial
database state and later changes to file in the text-based DDlog command format.
The ovn_northd_cli program can later replay these changes for debugging purposes.
This option has a performance impact. See debugging-ddlog.rst in the OVN
documentation for more details.
--dry-run
Causes ovn-northd to start paused. In the paused state, ovn-northd does not apply
any changes to the databases, although it continues to monitor them. For more
information, see the pause command, under Runtime Management Commands below.
For ovn-northd-ddlog, one could use this option with --ddlog-record to generate a
replay log without restarting a process or disturbing a running system.
n-threads N
In certain situations, it may be desirable to enable parallelization on a system to
decrease latency (at the potential cost of increasing CPU usage).
This option will cause ovn-northd to use N threads when building logical flows,
when N is within [2-256]. If N is 1, parallelization is disabled (default
behavior). If N is less than 1, then N is set to 1, parallelization is disabled and
a warning is logged. If N is more than 256, then N is set to 256, parallelization
is enabled (with 256 threads) and a warning is logged.
ovn-northd-ddlog does not support this option.
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 determined 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 ovn-northd. When it is paused, ovn-northd receives changes from the
Northbound and Southbound database changes as usual, but it does not send
any updates. A paused ovn-northd also drops database locks, which allows any
other non-paused instance of ovn-northd to take over.
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.
sb-cluster-state-reset
Reset southbound database cluster status when databases are destroyed and
rebuilt.
If all databases in a clustered southbound database are removed from disk,
then the stored index of all databases will be reset to zero. This will
cause ovn-northd to be unable to read or write to the southbound database,
because it will always detect the data as stale. In such a case, run this
command so that ovn-northd will reset its local index so that it can
interact with the southbound database again.
nb-cluster-state-reset
Reset northbound database cluster status when databases are destroyed and
rebuilt.
This performs the same task as sb-cluster-state-reset except for the
northbound database client.
set-n-threads N
Set the number of threads used for building logical flows. When N is within
[2-256], parallelization is enabled. When N is 1 parallelization is
disabled. When N is less than 1 or more than 256, an error is returned. If
ovn-northd fails to start parallelization (e.g. fails to setup semaphores,
parallelization is disabled and an error is returned.
get-n-threads
Return the number of threads used for building logical flows.
inc-engine/show-stats
Display ovn-northd engine counters. For each engine node the following
counters have been added:
• recompute
• compute
• abort
inc-engine/show-stats engine_node_name counter_name
Display the ovn-northd engine counter(s) for the specified engine_node_name.
counter_name is optional and can be one of recompute, compute or abort.
inc-engine/clear-stats
Reset ovn-northd engine counters.
Only ovn-northd-ddlog supports the following commands:
enable-cpu-profiling
disable-cpu-profiling
Enables or disables profiling of CPU time used by the DDlog engine. When CPU
profiling is enabled, the profile command (see below) will include DDlog CPU
usage statistics in its output. Enabling CPU profiling will slow
ovn-northd-ddlog. Disabling CPU profiling does not clear any previously
recorded statistics.
profile
Outputs a profile of the current and peak sizes of arrangements inside DDlog.
This profiling data can be useful for optimizing DDlog code. If CPU profiling
was previously enabled (even if it was later disabled), the output also
includes a CPU time profile. See Profiling inside the tutorial in the DDlog
repository for an introduction to profiling DDlog.
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 check
Ingress table 0 contains these logical flows:
• Priority 100 flows to drop packets with VLAN tags or multicast Ethernet
source addresses.
• For each disabled logical port, a priority 100 flow is added which matches
on all packets and applies the action REGBIT_PORT_SEC_DROP" = 1; next;" so
that the packets are dropped in the next stage.
• For each (enabled) vtep logical port, a priority 70 flow is added which
matches on all packets and applies the action next(pipeline=ingress,
table=S_SWITCH_IN_L2_LKUP) = 1; to skip most stages of ingress pipeline and
go directly to ingress L2 lookup table to determine the output port. Packets
from VTEP (RAMP) switch should not be subjected to any ACL checks. Egress
pipeline will do the ACL checks.
• For each enabled logical port configured with qdisc queue id in the
options:qdisc_queue_id column of Logical_Switch_Port, a priority 70 flow is
added which matches on all packets and applies the action set_queue(id);
REGBIT_PORT_SEC_DROP" = check_in_port_sec(); next;".
• A priority 1 flow is added which matches on all packets for all the logical
ports and applies the action REGBIT_PORT_SEC_DROP" = check_in_port_sec();
next; to evaluate the port security. The action check_in_port_sec applies
the port security rules defined in the port_security column of
Logical_Switch_Port table.
Ingress Table 1: Ingress Port Security - Apply
This table drops the packets if the port security check failed in the previous stage i.e
the register bit REGBIT_PORT_SEC_DROP is set to 1.
Ingress table 1 contains these logical flows:
• A priority-50 fallback flow that drops the packet if the register bit
REGBIT_PORT_SEC_DROP is set to 1.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 2: Lookup MAC address learning table
This table looks up the MAC learning table of the logical switch datapath to check if the
port-mac pair is present or not. MAC is learnt only for logical switch VIF ports whose
port security is disabled and ’unknown’ address set.
• For each such logical port p whose port security is disabled and ’unknown’
address set following flow is added.
• Priority 100 flow with the match inport == p and action reg0[11] =
lookup_fdb(inport, eth.src); next;
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 3: Learn MAC of ’unknown’ ports.
This table learns the MAC addresses seen on the logical ports whose port security is
disabled and ’unknown’ address set if the lookup_fdb action returned false in the previous
table.
• For each such logical port p whose port security is disabled and ’unknown’
address set following flow is added.
• Priority 100 flow with the match inport == p && reg0[11] == 0 and
action put_fdb(inport, eth.src); next; which stores the port-mac in
the mac learning table of the logical switch datapath and advances
the packet to the next table.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 4: 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.
Multicast, IPv6 Neighbor Discovery and MLD traffic also skips stateful ACLs. For "allow-
stateless" ACLs, a flow is added to bypass setting the hint for connection tracker
processing when there are stateful ACLs or LB rules; REGBIT_ACL_STATELESS is set for
traffic matching stateless ACL flows.
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 column of NB_Global table.
Ingress Table 5: 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 two priority-110 flows to move multicast, IPv6 Neighbor
Discovery and MLD traffic to the next table. It also contains two priority-110 flows to
move stateless traffic, i.e traffic for which REGBIT_ACL_STATELESS is set, 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 with
the match ip to match on IP packets and sets the action reg0[2] = 1; next; to act as a
hint for table Pre-stateful to send IP packets to the connection tracker for packet de-
fragmentation (and to possibly do DNAT for already established load balanced traffic)
before eventually advancing to ingress table Stateful. 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
Prior to OVN 20.09 we were setting the reg0[0] = 1 only if the IP destination matches the
load balancer VIP. However this had few issues cases where a logical switch doesn’t have
any ACLs with allow-related action. To understand the issue lets a take a TCP load
balancer - 10.0.0.10:80=10.0.0.3:80. If a logical port - p1 with IP - 10.0.0.5 opens a TCP
connection with the VIP - 10.0.0.10, then the packet in the ingress pipeline of ’p1’ is
sent to the p1’s conntrack zone id and the packet is load balanced to the backend -
10.0.0.3. For the reply packet from the backend lport, it is not sent to the conntrack of
backend lport’s zone id. This is fine as long as the packet is valid. Suppose the backend
lport sends an invalid TCP packet (like incorrect sequence number), the packet gets
delivered to the lport ’p1’ without unDNATing the packet to the VIP - 10.0.0.10. And this
causes the connection to be reset by the lport p1’s VIF.
We can’t fix this issue by adding a logical flow to drop ct.inv packets in the egress
pipeline since it will drop all other connections not destined to the load balancers. To
fix this issue, we send all the packets to the conntrack in the ingress pipeline if a load
balancer is configured. We can now add a lflow to drop ct.inv packets.
This table also has priority-120 flows that punt all IGMP/MLD packets to ovn-controller if
the switch is an interconnect switch with multicast snooping enabled.
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 column of NB_Global table.
This table also has a priority-110 flow with the match inport == I for all logical switch
datapaths to move traffic to the next table. Where I is the peer of a logical router port.
This flow is added to skip the connection tracking of packets which enter from logical
router datapath to logical switch datapath.
Ingress Table 6: 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.
• Priority-120 flows that send the packets to connection tracker using
ct_lb_mark; as the action so that the already established traffic destined
to the load balancer VIP gets DNATted. These flows match each VIPs IP and
port. For IPv4 traffic the flows also load the original destination IP and
transport port in registers reg1 and reg2. For IPv6 traffic the flows also
load the original destination IP and transport port in registers xxreg1 and
reg2.
• A priority-110 flow sends the packets that don’t match the above flows to
connection tracker based on a hint provided by the previous tables (with a
match for reg0[2] == 1) by using the ct_lb_mark; action.
• 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 7: from-lport ACL hints
This table consists of logical flows that set hints (reg0 bits) to be used in the next
stage, in the ACL processing table, if stateful ACLs or load balancers are configured.
Multiple hints can be set for the same packet. The possible hints are:
• reg0[7]: the packet might match an allow-related ACL and might have to
commit the connection to conntrack.
• reg0[8]: the packet might match an allow-related ACL but there will be no
need to commit the connection to conntrack because it already exists.
• reg0[9]: the packet might match a drop/reject.
• reg0[10]: the packet might match a drop/reject ACL but the connection was
previously allowed so it might have to be committed again with ct_label=1/1.
The table contains the following flows:
• A priority-65535 flow to advance to the next table if the logical switch has
no ACLs configured, otherwise a priority-0 flow to advance to the next
table.
• A priority-7 flow that matches on packets that initiate a new session. This
flow sets reg0[7] and reg0[9] and then advances to the next table.
• A priority-6 flow that matches on packets that are in the request direction
of an already existing session that has been marked as blocked. This flow
sets reg0[7] and reg0[9] and then advances to the next table.
• A priority-5 flow that matches untracked packets. This flow sets reg0[8] and
reg0[9] and then advances to the next table.
• A priority-4 flow that matches on packets that are in the request direction
of an already existing session that has not been marked as blocked. This
flow sets reg0[8] and reg0[10] and then advances to the next table.
• A priority-3 flow that matches on packets that are in not part of
established sessions. This flow sets reg0[9] and then advances to the next
table.
• A priority-2 flow that matches on packets that are part of an established
session that has been marked as blocked. This flow sets reg0[9] and then
advances to the next table.
• A priority-1 flow that matches on packets that are part of an established
session that has not been marked as blocked. This flow sets reg0[10] and
then advances to the next table.
Ingress table 8: from-lport ACL evaluation before LB
Logical flows in this table closely reproduce those in the ACL table in the OVN_Northbound
database for the from-lport direction without the option apply-after-lb set or set to
false. 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.
• This table is responsible for evaluating ACLs, and setting a register bit to
indicate whether the ACL decided to allow, drop, or reject the traffic. The
allow bit is reg8[16]. The drop bit is reg8[17]. All flows in this table
will advance the packet to the next table, where the bits from before are
evaluated to determine what to do with the packet. Any flows in this table
that intend for the packet to pass will set reg8[16] to 1, even if an ACL
with an allow-type action was not matched. This lets the next table know to
allow the traffic to pass. These bits will be referred to as the "allow",
"drop", and "reject" bits in the upcoming paragraphs.
• If the tier column has been configured on the ACL, then OVN will also match
the current tier counter against the configured ACL tier. OVN keeps count of
the current tier in reg8[30..31].
• allow ACLs translate into logical flows that set the allow bit to 1 and
advance the packet to the next table. If there are any stateful ACLs on this
datapath, then allow ACLs set the allow bit to one and in addition perform
ct_commit; (which acts as a hint for future tables to commit the connection
to conntrack). In case the ACL has a label then reg3 is loaded with the
label value and reg0[13] bit is set to 1 (which acts as a hint for the next
tables to commit the label to conntrack).
• allow-related ACLs translate into logical flows that set the allow bit and
additionally have ct_commit(ct_label=0/1); next; actions for new connections
and reg0[1] = 1; next; for existing connections. In case the ACL has a label
then reg3 is loaded with the label value and reg0[13] bit is set to 1 (which
acts as a hint for the next tables to commit the label to conntrack).
• allow-stateless ACLs translate into logical flows that set the allow bit and
advance to the next table.
• reject ACLs translate into logical flows with that set the reject bit and
advance to the next table.
• pass ACLs translate into logical flows that do not set the allow, drop, or
reject bit and advance to the next table.
• Other ACLs set the drop bit and advance to the next table for new or
untracked connections. For known connections, they set the drop bit, as well
as running the ct_commit(ct_label=1/1); action. 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 contains a priority-65535 flow to set the allow bit and advance to the next
table if the logical switch has no ACLs configured, otherwise a priority-0 flow to advance
to the next table is added. This flow does not set the allow bit, so that the next table
can decide whether to allow or drop the packet based on the value of the
options:default_acl_drop column of the NB_Global table.
A priority-65532 flow is added that sets the allow bit for IPv6 Neighbor solicitation,
Neighbor discover, Router solicitation, Router advertisement and MLD packets regardless of
other ACLs defined.
If the logical datapath has a stateful ACL or a load balancer with VIP configured, the
following flows will also be added:
• If options:default_acl_drop column of NB_Global is false or not set, a
priority-1 flow that sets the hint to commit IP traffic that is not part of
established sessions 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-1 flow that sets the allow bit and 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-65532 flow that sets the allow bit for 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_mark.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_mark.blocked will get set
and packets in the reply direction will no longer be allowed, either. This
flow also clears the register bits reg0[9] and reg0[10] and sets register
bit reg0[17]. If ACL logging and logging of related packets is enabled, then
a companion priority-65533 flow will be installed that accomplishes the same
thing but also logs the traffic.
• A priority-65532 flow that sets the allow bit for 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_mark.blocked set. This flow also applies NAT
to the related traffic so that ICMP headers and the inner packet have
correct addresses. If ACL logging and logging of related packets is enabled,
then a companion priority-65533 flow will be installed that accomplishes the
same thing but also logs the traffic.
• A priority-65532 flow that sets the drop bit for all traffic marked by the
connection tracker as invalid.
• A priority-65532 flow that sets the drop bit for all traffic in the reply
direction with ct_mark.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.
If the logical datapath has any ACL or a load balancer with VIP configured, the following
flow will also be added:
• 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 that sets the allow bit, where E is the service monitor mac
defined in the options:svc_monitor_mac column of NB_Global table.
Ingress Table 9: from-lport ACL action
Logical flows in this table decide how to proceed based on the values of the allow, drop,
and reject bits that may have been set in the previous table.
• If no ACLs are configured, then a priority 0 flow is installed that matches
everything and advances to the next table.
• A priority 1000 flow is installed that will advance the packet to the next
table if the allow bit is set.
• A priority 1000 flow is installed that will run the drop; action if the drop
bit is set.
• A priority 1000 flow is installed that will run the tcp_reset { output <->
inport; next(pipeline=egress,table=5);} action for TCP
connections,icmp4/icmp6 action for UDP connections, and sctp_abort {output
<-%gt; inport; next(pipeline=egress,table=5);} action for SCTP associations.
• If any ACLs have tiers configured on them, then three priority 500 flows are
installed. If the current tier counter is 0, 1, or 2, then the current tier
counter is incremented by one and the packet is sent back to the previous
table for re-evaluation.
Ingress Table 10: 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 11: 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 priority mentioned in the QoS table.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 12: Load balancing affinity check
Load balancing affinity check table contains the following logical flows:
• For all the configured load balancing rules for a switch in OVN_Northbound
database where a positive affinity timeout is specified in options column,
that includes a L4 port PORT of protocol P and IP address VIP, a
priority-100 flow is added. For IPv4 VIPs, the flow matches ct.new && ip &&
ip4.dst == VIP && P.dst == PORT. For IPv6 VIPs, the flow matches ct.new &&
ip && ip6.dst == VIP&& P && P.dst == PORT. The flow’s action is reg9[6] =
chk_lb_aff(); next;.
• A priority 0 flow is added which matches on all packets and applies the
action next;.
Ingress Table 13: LB
• For all the configured load balancing rules for a switch in OVN_Northbound
database where a positive affinity timeout is specified in options column,
that includes a L4 port PORT of protocol P and IP address VIP, a
priority-150 flow is added. For IPv4 VIPs, the flow matches reg9[6] == 1 &&
ct.new && ip && ip4.dst == VIP && P.dst == PORT . For IPv6 VIPs, the flow
matches reg9[6] == 1 && ct.new && ip && ip6.dst == VIP && P && P.dst ==
PORT. The flow’s action is ct_lb_mark(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.
• 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.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_mark(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
IPv4 traffic the flow also loads the original destination IP and transport
port in registers reg1 and reg2. For IPv6 traffic the flow also loads the
original destination IP and transport port in registers xxreg1 and reg2. The
above flow is created even if the load balancer is attached to a logical
router connected to the current logical switch and the
install_ls_lb_from_router variable in options is set to true.
• 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_mark(args), where args contains comma separated
IP addresses of the same address family as VIP. For IPv4 traffic the flow
also loads the original destination IP and transport port in registers reg1
and reg2. For IPv6 traffic the flow also loads the original destination IP
and transport port in registers xxreg1 and reg2. The above flow is created
even if the load balancer is attached to a logical router connected to the
current logical switch and the install_ls_lb_from_router variable in options
is set to true.
• If the load balancer is created with --reject option and it has no active
backends, a TCP reset segment (for tcp) or an ICMP port unreachable packet
(for all other kind of traffic) will be sent whenever an incoming packet is
received for this load-balancer. Please note using --reject option will
disable empty_lb SB controller event for this load balancer.
Ingress Table 14: Load balancing affinity learn
Load balancing affinity learn table contains the following logical flows:
• For all the configured load balancing rules for a switch in OVN_Northbound
database where a positive affinity timeout T is specified in options column,
that includes a L4 port PORT of protocol P and IP address VIP, a
priority-100 flow is added. For IPv4 VIPs, the flow matches reg9[6] == 0 &&
ct.new && ip && ip4.dst == VIP && P.dst == PORT. For IPv6 VIPs, the flow
matches ct.new && ip && ip6.dst == VIP && P && P.dst == PORT . The flow’s
action is commit_lb_aff(vip = VIP:PORT, backend = backend ip: backend port,
proto = P, timeout = T); .
• A priority 0 flow is added which matches on all packets and applies the
action next;.
Ingress Table 15: Pre-Hairpin
• If the logical switch has load balancer(s) configured, then a priority-100
flow is added with the match ip && ct.trk to check if the packet needs to be
hairpinned (if after load balancing the destination IP matches the source
IP) or not by executing the actions reg0[6] = chk_lb_hairpin(); and reg0[12]
= chk_lb_hairpin_reply(); and advances the packet to the next table.
• A priority-0 flow that simply moves traffic to the next table.
Ingress Table 16: Nat-Hairpin
• If the logical switch has load balancer(s) configured, then a priority-100
flow is added with the match ip && ct.new && ct.trk && reg0[6] == 1 which
hairpins the traffic by NATting source IP to the load balancer VIP by
executing the action ct_snat_to_vip and advances the packet to the next
table.
• If the logical switch has load balancer(s) configured, then a priority-100
flow is added with the match ip && ct.est && ct.trk && reg0[6] == 1 which
hairpins the traffic by NATting source IP to the load balancer VIP by
executing the action ct_snat and advances the packet to the next table.
• If the logical switch has load balancer(s) configured, then a priority-90
flow is added with the match ip && reg0[12] == 1 which matches on the
replies of hairpinned traffic (i.e., destination IP is VIP, source IP is the
backend IP and source L4 port is backend port for L4 load balancers) and
executes ct_snat and advances the packet to the next table.
• A priority-0 flow that simply moves traffic to the next table.
Ingress Table 17: Hairpin
• If logical switch has attached logical switch port of vtep type, then for
each distributed gateway router port RP attached to this logical switch and
has chassis redirect port cr-RP, a priority-2000 flow is added with the
match .IP
reg0[14] == 1 && is_chassis_resident(cr-RP)
and action next;.
reg0[14] register bit is set in the ingress L2 port security check table for
traffic received from HW VTEP (ramp) ports.
• If logical switch has attached logical switch port of vtep type, then a
priority-1000 flow that matches on reg0[14] register bit for the traffic
received from HW VTEP (ramp) ports. This traffic is passed to ingress table
ls_in_l2_lkup.
• 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 18: from-lport ACL evaluation after LB
Logical flows in this table closely reproduce those in the ACL eval table in the
OVN_Northbound database for the from-lport direction with the option apply-after-lb set to
true. 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. The flows in
this table indicate the ACL verdict by setting reg8[16] for allow-type ACLs, reg8[17] for
drop ACLs, and reg8[17] for reject ACLs, and then advancing the packet to the next table.
These will be reffered to as the allow bit, drop bit, and reject bit throughout the
documentation for this table and the next one.
Like with ACLs that are evaluated before load balancers, if the ACL is configured with a
tier value, then the current tier counter, supplied in reg8[30..31] is matched against the
ACL’s configured tier in addition to the ACL’s match.
• allow apply-after-lb ACLs translate into logical flows that set the allow
bit. If there are any stateful ACLs (including both before-lb and after-lb
ACLs) on this datapath, then allow ACLs also run ct_commit; next; (which
acts as a hint for an upcoming table to commit the connection to conntrack).
In case the ACL has a label then reg3 is loaded with the label value and
reg0[13] bit is set to 1 (which acts as a hint for the next tables to commit
the label to conntrack).
• allow-related apply-after-lb ACLs translate into logical flows that set the
allow bit and run the ct_commit(ct_label=0/1); next; actions for new
connections and reg0[1] = 1; next; for existing connections. In case the ACL
has a label then reg3 is loaded with the label value and reg0[13] bit is set
to 1 (which acts as a hint for the next tables to commit the label to
conntrack).
• allow-stateless apply-after-lb ACLs translate into logical flows that set
the allow bit and advance to the next table.
• reject apply-after-lb ACLs translate into logical flows that set the reject
bit and advance to the next table.
• pass apply-after-lb ACLs translate into logical flows that do not set the
allow, drop, or reject bit and advance to the next table.
• Other apply-after-lb ACLs set the drop bit 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.
• One priority-65532 flow matching packets with reg0[17] set (either replies
to existing sessions or traffic related to existing sessions) and allows
these by setting the allow bit and advancing to the next table.
• One priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 19: from-lport ACL action after LB
Logical flows in this table decide how to proceed based on the values of the allow, drop,
and reject bits that may have been set in the previous table.
• If no ACLs are configured, then a priority 0 flow is installed that matches
everything and advances to the next table.
• A priority 1000 flow is installed that will advance the packet to the next
table if the allow bit is set.
• A priority 1000 flow is installed that will run the drop; action if the drop
bit is set.
• A priority 1000 flow is installed that will run the tcp_reset { output <->
inport; next(pipeline=egress,table=5);} action for TCP
connections,icmp4/icmp6 action for UDP connections, and sctp_abort {output
<-%gt; inport; next(pipeline=egress,table=5);} action for SCTP associations.
• If any ACLs have tiers configured on them, then three priority 500 flows are
installed. If the current tier counter is 0, 1, or 2, then the current tier
counter is incremented by one and the packet is sent back to the previous
table for re-evaluation.
Ingress Table 20: Stateful
• A priority 100 flow is added which commits the packet to the conntrack and
sets the most significant 32-bits of ct_label with the reg3 value based on
the hint provided by previous tables (with a match for reg0[1] == 1 &&
reg0[13] == 1). This is used by the ACLs with label to commit the label
value to conntrack.
• For ACLs without label, a second 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 && reg0[13] == 0).
• A priority-0 flow that simply moves traffic to the next table.
Ingress Table 21: 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 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:
• If packet was received from HW VTEP (ramp switch), and this packet is ARP or
Neighbor Solicitation, such packet is passed to next table with max
proirity. ARP/ND requests from HW VTEP must be handled in logical router
ingress pipeline.
• If the logical switch has no router ports with options:arp_proxy configured
add a priority-100 flows to skip the ARP responder if inport is of type
localnet advances directly to the next table. ARP requests sent to localnet
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 flows 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))
inport == P && && ((nd_ns && ip6.dst == {VIP, NS_MULTICAST_ADDR} && nd.target == VIP) || (nd_na && nd.target == 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 and
NS_MULTICAST_ADDR is solicited-node multicast address corresponding to the
VIP.
• 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 (unless ignore_lsp_down is configured as true
in options column of NB_Global table of the Northbound database), for
logical ports of type virtual, for logical ports with ’unknown’ address set
and for logical ports of a logical switch configured with
other_config:vlan-passthru=true.
The above ARP responder flows are added for the list of IPv4 addresses if
defined in options:arp_proxy column of Logical_Switch_Port table for logical
switch ports of type router.
• 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 (unless ignore_lsp_down is configured as true
in options column of NB_Global table of the Northbound database), for
logical ports of type virtual and for logical ports with ’unknown’ address
set.
The above NDP responder flows are added for the list of IPv6 addresses if
defined in options:arp_proxy column of Logical_Switch_Port table for logical
switch ports of type router.
• 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 IPv6 the similar flow is added with the following action
nd_na {
eth.dst = eth.src;
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
• 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 22: 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 16.
Ingress Table 23: 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 17.
Ingress Table 24 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 25 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 26 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-100 flow is added for each external logical port which doesn’t
reside on a chassis to drop any packet destined to the router mac - with the
match inport == external && eth.src == E && eth.dst == R &&
!is_chassis_resident("external") where E is the external port mac and R is
the router port mac.
• A priority-0 flow that matches all packets to advances to table 20.
Ingress Table 27 Destination Lookup
This table implements switching behavior. It contains these logical flows:
• A priority-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 column 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.
• 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_L2 multicast group, which ovn-northd populates
with all non-router 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 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 to the MC_FLOOD_L2 multicast group which
contains all non-router logical ports.
• Priority-75 flows for each port connected to a logical router matching self
originated ARP request/RARP request/ND packets. These packets are flooded to
the MC_FLOOD_L2 which contains all non-router logical ports.
• A priority-72 flow that outputs all ARP requests and ND packets with an
Ethernet broadcast or multicast eth.dst to the MC_FLOOD_L2 multicast group
if other_config:broadcast-arps-to-all-routers=true.
• 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. Action of this flow outputs the packet to the single associated
output port if it is enabled. drop; action is applied if LSP is disabled.
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 has a gateway chassis:
• The flow for the connected logical router port’s Ethernet address is
only programmed on the gateway 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
distributed gateway LRP:
• The flow for the connected logical router port’s Ethernet address is
only programmed on the gateway 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 with the action
outport = get_fdb(eth.dst); next;. The action get_fdb gets the port for the
eth.dst in the MAC learning table of the logical switch datapath. If there
is no entry for eth.dst in the MAC learning table, then it stores none in
the outport.
Ingress Table 28 Destination unknown
This table handles the packets whose destination was not found or and looked up in the MAC
learning table of the logical switch datapath. It contains the following flows.
• Priority 50 flow with the match outport == P is added for each disabled
Logical Switch Port P. This flow has action drop;.
• If the logical switch has logical ports with ’unknown’ addresses set, then
the below logical flow is added
• Priority 50 flow with the match outport == "none" then 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.
If the logical switch has no logical ports with ’unknown’ address set, then
the below logical flow is added
• Priority 50 flow with the match outport == none and drops the
packets.
• One priority-0 fallback flow that outputs the packet to the egress stage
with the outport learnt from get_fdb action.
Egress Table 0: 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 column of NB_Global table.
This table also has a priority-110 flow with the match outport == I for all logical switch
datapaths to move traffic to the next table. Where I is the peer of a logical router port.
This flow is added to skip the connection tracking of packets which will be entering
logical router datapath from logical switch datapath for routing.
Egress Table 1: 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 two priority-110 flows to move
multicast, IPv6 Neighbor Discovery and MLD 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[2] = 1; next; to act as a hint for table Pre-stateful to send IP
packets to the connection tracker for packet de-fragmentation and possibly DNAT the
destination VIP to one of the selected backend for already committed load balanced
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 column of NB_Global table.
This table also has a priority-110 flow with the match outport == I for all logical switch
datapaths to move traffic to the next table, and, if there are no stateful_acl, clear the
ct_state. Where I is the peer of a logical router port. This flow is added to skip the
connection tracking of packets which will be entering logical router datapath from logical
switch datapath for routing.
Egress Table 2: Pre-stateful
This is similar to ingress table Pre-stateful. This table adds the below 3 logical flows.
• A Priority-120 flow that send the packets to connection tracker using
ct_lb_mark; as the action so that the already established traffic gets
unDNATted from the backend IP to the load balancer VIP based on a hint
provided by the previous tables with a match for reg0[2] == 1. If the packet
was not DNATted earlier, then ct_lb_mark functions like ct_next.
• 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.
• A priority-0 flow that matches all packets to advance to the next table.
Egress Table 3: from-lport ACL hints
This is similar to ingress table ACL hints.
Egress Table 4: to-lport ACL evaluation
This is similar to ingress table ACL eval except for to-lport ACLs. As a reminder, these
flows use the following register bits to indicate their verdicts. Allow-type ACLs set
reg8[16], drop ACLs set reg8[17], and reject ACLs set reg8[18].
Also like with ingress ACLs, egress ACLs can have a configured tier. If a tier is
configured, then the current tier counter is evaluated against the ACL’s configured tier
in addition to the ACL’s match. The current tier counter is stored in reg8[30..31].
Similar to ingress table, a priority-65532 flow is added to allow IPv6 Neighbor
solicitation, Neighbor discover, Router solicitation, Router advertisement and MLD packets
regardless of other ACLs defined.
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 18:
DHCP responses. This is indicated by setting the allow bit.
• 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 20: DNS responses. This is indicated by
setting the allow bit.
• 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 column of NB_Global table. This is
indicated by setting the allow bit.
Egress Table 5: to-lport ACL action
This is similar to ingress table ACL action.
Egress Table 6: to-lport QoS Marking
This is similar to ingress table QoS marking except they apply to to-lport QoS rules.
Egress Table 7: to-lport QoS Meter
This is similar to ingress table QoS meter except they apply to to-lport QoS rules.
Egress Table 8: Stateful
This is similar to ingress table Stateful except that there are no rules added for load
balancing new connections.
Egress Table 9: Egress Port Security - check
This is similar to the port security logic in table Ingress Port Security check except
that action check_out_port_sec is used to check the port security rules. This table adds
the below logical flows.
• A priority 100 flow which matches on the multicast traffic and applies the
action REGBIT_PORT_SEC_DROP" = 0; next;" to skip the out port security
checks.
• A priority 0 logical flow is added which matches on all the packets and
applies the action REGBIT_PORT_SEC_DROP" = check_out_port_sec(); next;". The
action check_out_port_sec applies the port security rules based on the
addresses defined in the port_security column of Logical_Switch_Port table
before delivering the packet to the outport.
Egress Table 10: Egress Port Security - Apply
This is similar to the ingress port security logic in ingress table A Ingress Port
Security - Apply. This table drops the packets if the port security check failed in the
previous stage i.e the register bit REGBIT_PORT_SEC_DROP is set to 1.
The following flows are added.
• For each port configured with egress qos in the options:qdisc_queue_id
column of Logical_Switch_Port, running a localnet port on the same logical
switch, a priority 110 flow is added which matches on the localnet outport
and on the port inport and applies the action set_queue(id); output;".
• For each localnet port configured with egress qos in the
options:qdisc_queue_id column of Logical_Switch_Port, a priority 100 flow is
added which matches on the localnet outport and applies the action
set_queue(id); output;".
Please remember to mark the corresponding physical interface with
ovn-egress-iface set to true in external_ids.
• A priority-50 flow that drops the packet if the register bit
REGBIT_PORT_SEC_DROP is set to 1.
• A priority-0 flow that outputs the packet to the outport.
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), stores the router
port ethernet address and advances to next table, with action
xreg0[0..47]=E; next;.
For the gateway port on a distributed logical router (where one of the
logical router ports specifies a gateway chassis), the above flow matching
eth.dst == E is only programmed on the gateway port instance on the gateway
chassis. If LRP’s logical switch has attached LSP of vtep type, the
is_chassis_resident() part is not added to lflow to allow traffic originated
from logical switch to reach LR services (LBs, NAT).
For a distributed logical router or for gateway router where the port is
configured with options:gateway_mtu the action of the above flow is modified
adding check_pkt_larger in order to mark the packet setting
REGBIT_PKT_LARGER if the size is greater than the MTU. If the port is also
configured with options:gateway_mtu_bypass then another flow is added, with
priority-55, to bypass the check_pkt_larger flow. This is useful for traffic
that normally doesn’t need to be fragmented and for which check_pkt_larger,
which might not be offloadable, is not really needed. One such example is
TCP traffic.
• 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 distributed gateway port
corresponding to the NAT rule (specified or inferred), with action
xreg0[0..47]=E; next;.
This flow is only programmed on the gateway port instance on the chassis
where the logical_port specified in the NAT rule resides.
• A priority-0 logical flow that matches all packets not already handled
(match 1) and drops them (action drop;).
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, if the option always_learn_from_arp_request is true
for this router, a priority-100 flow is added which matches inport == P &&
arp.spa == S/L && arp.op == 1 (ARP request) with the following actions:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
next;
If the option always_learn_from_arp_request is false, the following two
flows are added.
A priority-110 flow is added which matches inport == P && arp.spa == S/L &&
arp.tpa == A && arp.op == 1 (ARP request) with the following actions:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
reg9[3] = 1;
next;
A priority-100 flow is added which matches inport == P && arp.spa == S/L &&
arp.op == 1 (ARP request) with the following actions:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
reg9[3] = lookup_arp_ip(inport, arp.spa);
next;
If the logical router port P is a distributed gateway router port,
additional match is_chassis_resident(cr-P) is added for all these flows.
• A priority-100 flow which matches on ARP reply packets and applies the
actions if the option always_learn_from_arp_request is true:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
next;
If the option always_learn_from_arp_request is false, the above actions will
be:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
reg9[3] = 1;
next;
• A priority-100 flow which matches on IPv6 Neighbor Discovery advertisement
packet and applies the actions if the option always_learn_from_arp_request
is true:
reg9[2] = lookup_nd(inport, nd.target, nd.tll);
next;
If the option always_learn_from_arp_request is false, the above actions will
be:
reg9[2] = lookup_nd(inport, nd.target, nd.tll);
reg9[3] = 1;
next;
• A priority-100 flow which matches on IPv6 Neighbor Discovery solicitation
packet and applies the actions if the option always_learn_from_arp_request
is true:
reg9[2] = lookup_nd(inport, ip6.src, nd.sll);
next;
If the option always_learn_from_arp_request is false, the above actions will
be:
reg9[2] = lookup_nd(inport, ip6.src, nd.sll);
reg9[3] = lookup_nd_ip(inport, ip6.src);
next;
• A priority-0 fallback flow that matches all packets and applies the action
reg9[2] = 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 it is needed according to the lookup results from
the previous stage.
reg9[2] will be 1 if the lookup_arp/lookup_nd in the previous table was successful or
skipped, meaning no need to learn mac binding from the packet.
reg9[3] will be 1 if the lookup_arp_ip/lookup_nd_ip in the previous table was successful
or skipped, meaning it is ok to learn mac binding from the packet (if reg9[2] is 0).
• A priority-100 flow with the match reg9[2] == 1 || reg9[3] == 0 and advances
the packet to the next table as there is no need to learn the neighbor.
• A priority-95 flow with the match nd_ns && (ip6.src == 0 || nd.sll == 0) and
applies the action next;
• A priority-90 flow with the match arp and applies the action put_arp(inport,
arp.spa, arp.sha); next;
• A priority-95 flow with the match nd_na && nd.tll == 0 and applies the
action put_nd(inport, nd.target, eth.src); 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;
• A priority-0 logical flow that matches all packets not already handled
(match 1) and drops them (action drop;).
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 dnat_and_snat NAT rule on a distributed logical routers or gateway
routers with gateway port configured with options:gateway_mtu to a valid
integer value M, a priority-160 flow with the match inport == LRP &&
REGBIT_PKT_LARGER && REGBIT_EGRESS_LOOPBACK == 0, where LRP is the logical
router port and applies the following action for ipv4 and ipv6 respectively:
icmp4_error {
icmp4.type = 3; /* Destination Unreachable. */
icmp4.code = 4; /* Frag Needed and DF was Set. */
icmp4.frag_mtu = M;
eth.dst = eth.src;
eth.src = E;
ip4.dst = ip4.src;
ip4.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
outport = LRP;
flags.loopback = 1;
output;
};
icmp6_error {
icmp6.type = 2;
icmp6.code = 0;
icmp6.frag_mtu = M;
eth.dst = eth.src;
eth.src = E;
ip6.dst = ip6.src;
ip6.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
outport = LRP;
flags.loopback = 1;
output;
};
where E and I are the NAT rule external mac and IP respectively.
• For distributed logical routers or gateway routers with gateway port
configured with options:gateway_mtu to a valid integer value, a priority-150
flow with the match inport == LRP && REGBIT_PKT_LARGER &&
REGBIT_EGRESS_LOOPBACK == 0, where LRP is the logical router port and
applies the following action for ipv4 and ipv6 respectively:
icmp4_error {
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;
REGBIT_PKT_LARGER 0;
next(pipeline=ingress, table=0);
};
icmp6_error {
icmp6.type = 2;
icmp6.code = 0;
icmp6.frag_mtu = M;
eth.dst = E;
ip6.dst = ip6.src;
ip6.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
next(pipeline=ingress, table=0);
};
• For each NAT entry of a distributed logical router (with distributed gateway
router port(s)) of type snat, a priority-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 corresponding to the NAT entry (specified or
inferred) 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.
• For each BFD port the two following priority-110 flows are added to manage
BFD traffic:
• if ip4.src or ip6.src is any IP address owned by the router port and
udp.dst == 3784 , the packet is advanced to the next pipeline stage.
• if ip4.dst or ip6.dst is any IP address owned by the router port and
udp.dst == 3784 , the handle_bfd_msg action is executed.
• L3 admission control: Priority-120 flows allows IGMP and MLD packets if the
router has logical ports that have options :mcast_flood=’true’.
• 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.
• A priority-100 flow parses DHCPv6 replies from IPv6 prefix delegation
routers (udp.src == 547 && udp.dst == 546). The handle_dhcpv6_reply is used
to send IPv6 prefix delegation messages to the delegation 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 = xreg0[0..47];
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = xreg0[0..47];
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
For the gateway port on a distributed logical router (where one of the
logical router ports specifies a gateway chassis), the above flows are only
programmed on the gateway port instance on the gateway chassis. This
behavior avoids generation of multiple ARP responses from different chassis,
and allows upstream MAC learning to point to the gateway 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 gateway 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 gateway 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 = xreg0[0..47];
ip6.src = A;
nd.target = A;
nd.tll = xreg0[0..47];
outport = inport;
flags.loopback = 1;
output;
};
For the gateway port on a distributed logical router (where one of the
logical router ports specifies a gateway chassis), the above flows replying
to IPv6 Neighbor Solicitations are only programmed on the gateway port
instance on the gateway chassis. This behavior avoids generation of multiple
replies from different chassis, and allows upstream MAC learning to point to
the gateway chassis.
• These flows reply to ARP requests or IPv6 neighbor solicitation for the
virtual IP addresses configured in the router for NAT (both DNAT and SNAT)
or load balancing.
IPv4: For a configured NAT (both DNAT and SNAT) IP address or a load
balancer IPv4 VIP A, for each router port P with Ethernet address E, a
priority-90 flow matches arp.op == 1 && arp.tpa == A (ARP request) with the
following actions:
eth.dst = eth.src;
eth.src = xreg0[0..47];
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = xreg0[0..47];
arp.tpa <-> arp.spa;
outport = inport;
flags.loopback = 1;
output;
IPv4: For a configured load balancer IPv4 VIP, a similar flow is added with
the additional match inport == P if the VIP is reachable from any logical
router port of the logical router.
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 NAT (both DNAT and SNAT) IP address or a load
balancer IPv6 VIP A (if the VIP is reachable from any logical router port of
the logical router), 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 = xreg0[0..47];
nd.tll = xreg0[0..47];
ip6.src = A;
nd.target = A;
outport = inport;
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 gateway chassis):
• If the corresponding NAT rule cannot be handled in a distributed
manner, then a priority-92 flow is programmed on the gateway port
instance on the gateway chassis. A priority-91 drop flow is
programmed on the other chassis when ARP requests/NS packets are
received on the gateway port. This behavior avoids generation of
multiple ARP responses from different chassis, and allows upstream
MAC learning to point to the gateway 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 or if it
is used as a load balancer VIP.
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.
• Avoid ICMP time exceeded for multicast. A priority-32 flow with match ip.ttl
== {0, 1} && !ip.later_frag && (ip4.mcast || ip6.mcast) and actions drop;
drops multicast packets whose TTL has expired without sending ICMP time
exceeded.
• ICMP time exceeded. For each router port P, whose IP address is A, a
priority-31 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 = 254;
next;
};
icmp6 {
icmp6.type = 3; /* Time exceeded. */
icmp6.code = 0; /* TTL exceeded in transit. */
ip6.dst = ip6.src;
ip6.src = A;
ip.ttl = 254;
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: 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 4: 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 4: 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 is configured with lb_force_snat_ip=router_ip then for
every logical router port P attached to the Gateway router with the router
ip B, a priority-110 flow is added with the match inport == P && ip4.dst ==
B or inport == P && 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 next;.
A priority-0 logical flow with match 1 has actions next;.
Ingress Table 4: 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, two priority-100 flows are
added.
If the NAT rule cannot be handled in a distributed manner, then the below
priority-100 flows are only programmed on the gateway chassis.
• The first flow matches ip && ip4.dst == B && inport == GW
or ip && ip6.dst == B && inport == GW where GW is the distributed
gateway port corresponding to the NAT rule (specified or inferred),
with an action ct_snat; to unSNAT in the common zone. If the NAT rule
is of type dnat_and_snat and has stateless=true in the options, then
the action would be next;.
If the NAT entry is of type snat, then there is an additional match
is_chassis_resident(cr-GW)
where cr-GW is the chassis resident port of GW.
A priority-0 logical flow with match 1 has actions next;.
Ingress Table 5: 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.
For all load balancing rules that 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 applies the action ct_dnat; to send IP packets to the connection tracker
for packet de-fragmentation and to dnat the destination IP for the committed connection
before sending it to the next table.
If ECMP routes with symmetric reply are configured in the OVN_Northbound database for a
gateway router, a priority-100 flow is added for each router port on which symmetric
replies are configured. The matching logic for these ports essentially reverses the
configured logic of the ECMP route. So for instance, a route with a destination routing
policy will instead match if the source IP address matches the static route’s prefix. The
flow uses the actions chk_ecmp_nh_mac(); ct_next or chk_ecmp_nh(); ct_next to send IP
packets to table 76 or to table 77 in order to check if source info are already stored by
OVN and then to the connection tracker for packet de-fragmentation and tracking before
sending it to the next table.
If load balancing rules are configured in OVN_Northbound database for a Gateway router, a
priority 50 flow that matches icmp || icmp6 with an action of ct_dnat;, this allows
potentially related ICMP traffic to pass through CT.
Ingress Table 6: Load balancing affinity check
Load balancing affinity check table contains the following logical flows:
• For all the configured load balancing rules for a logical router where a
positive affinity timeout is specified in options column, that includes a L4
port PORT of protocol P and IPv4 or IPv6 address VIP, a priority-100 flow
that matches on ct.new && ip && ip.dst == VIP && P && P.dst == PORT (xxreg0
== VIP
in the IPv6 case) with an action of reg0 = ip.dst; reg9[16..31] = P.dst;
reg9[6] = chk_lb_aff(); next; (xxreg0 == ip6.dst in the IPv6 case)
• A priority 0 flow is added which matches on all packets and applies the
action next;.
Ingress Table 7: 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 7: 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 gateway chassis. These flows do not get
programmed for load balancers with IPv6 VIPs.
• For all the configured load balancing rules for a logical router where a
positive affinity timeout is specified in options column, that includes a L4
port PORT of protocol P and IPv4 or IPv6 address VIP, a priority-150 flow
that matches on reg9[6] == 1 && ct.new && ip && ip.dst == VIP && P && P.dst
== PORT with an action of ct_lb_mark(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 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 && !ct.rel && ip && ip.dst == VIP && P && P.dst ==
PORT with an action of ct_lb_mark(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_mark(args; force_snat);. If the load balancing rule is configured with
skip_snat set to true, the above action will be replaced by
flags.skip_snat_for_lb = 1; ct_lb_mark(args; skip_snat);. 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 just an IP address VIP to match on, a priority-110
flow that matches on ct.new && !ct.rel && ip4 && ip.dst == VIP with an
action of ct_lb_mark(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_mark(args; force_snat);. If the load balancing rule is configured with
skip_snat set to true, the above action will be replaced by
flags.skip_snat_for_lb = 1; ct_lb_mark(args; skip_snat);.
The previous table lr_in_defrag sets the register reg0 (or xxreg0 for IPv6)
and does ct_dnat. Hence for established traffic, this table just advances
the packet to the next stage.
• If the load balancer is created with --reject option and it has no active
backends, a TCP reset segment (for tcp) or an ICMP port unreachable packet
(for all other kind of traffic) will be sent whenever an incoming packet is
received for this load-balancer. Please note using --reject option will
disable empty_lb SB controller event for this load balancer.
• For the related traffic, a priority 50 flow that matches ct.rel && !ct.est
&& !ct.new with an action of ct_commit_nat;, if the router has load
balancer assigned to it. Along with two priority 70 flows that match
skip_snat and force_snat flags, setting the flags.force_snat_for_lb = 1 or
flags.skip_snat_for_lb = 1 accordingly.
• For the established traffic, a priority 50 flow that matches ct.est &&
!ct.rel && !ct.new && ct_mark.natted with an action of next;, if the router
has load balancer assigned to it. Along with two priority 70 flows that
match skip_snat and force_snat flags, setting the flags.force_snat_for_lb =
1 or flags.skip_snat_for_lb = 1 accordingly.
Ingress Table 7: 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).
If the NAT rule has allowed_ext_ips configured, then there is an additional
match ip4.src == allowed_ext_ips . Similarly, for IPV6, match would be
ip6.src == allowed_ext_ips.
If the NAT rule has exempted_ext_ips set, then there is an additional flow
configured at priority 101. The flow matches if source ip is an
exempted_ext_ip and the action is next; . This flow is used to bypass the
ct_dnat action for a packet originating from exempted_ext_ips.
• A priority-0 logical flow with match 1 has actions next;.
Ingress Table 7: 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 corresponding to the NAT rule (specified or inferred), 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 gateway chassis.
If the NAT rule has allowed_ext_ips configured, then there is an additional
match ip4.src == allowed_ext_ips . Similarly, for IPV6, match would be
ip6.src == allowed_ext_ips.
If the NAT rule has exempted_ext_ips set, then there is an additional flow
configured at priority 101. The flow matches if source ip is an
exempted_ext_ip and the action is next; . This flow is used to bypass the
ct_dnat action for a packet originating from exempted_ext_ips.
A priority-0 logical flow with match 1 has actions next;.
Ingress Table 8: Load balancing affinity learn
Load balancing affinity learn table contains the following logical flows:
• For all the configured load balancing rules for a logical router where a
positive affinity timeout T is specified in options
column, that includes a L4 port PORT of protocol P and IPv4 or IPv6 address
VIP, a priority-100 flow that matches on reg9[6] == 0 && ct.new && ip &&
reg0 == VIP && P && reg9[16..31] == PORT (xxreg0 == VIP in the IPv6 case)
with an action of commit_lb_aff(vip = VIP:PORT, backend = backend ip:
backend port, proto = P, timeout = T);.
• A priority 0 flow is added which matches on all packets and applies the
action next;.
Ingress Table 9: ECMP symmetric reply processing
• If ECMP routes with symmetric reply are configured in the OVN_Northbound
database for a gateway router, a priority-100 flow is added for each router
port on which symmetric replies are configured. The matching logic for these
ports essentially reverses the configured logic of the ECMP route. So for
instance, a route with a destination routing policy will instead match if
the source IP address matches the static route’s prefix. The flow uses the
action ct_commit { ct_label.ecmp_reply_eth = eth.src;" "
ct_mark.ecmp_reply_port = K;}; commit_ecmp_nh(); next;
to commit the connection and storing eth.src and the ECMP reply port
binding tunnel key K in the ct_label and the traffic pattern to table 76 or
77.
Ingress Table 10: 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 11: 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 12: IP Routing Pre
If a packet arrived at this table from Logical Router Port P which has options:route_table
value set, a logical flow with match inport == "P" with priority 100 and action setting
unique-generated per-datapath 32-bit value (non-zero) in OVS register 7. This register’s
value is checked in next table. If packet didn’t match any configured inport (<main> route
table), register 7 value is set to 0.
This table contains the following logical flows:
• Priority-100 flow with match inport == "LRP_NAME" value and action, which
set route table identifier in reg7.
A priority-0 logical flow with match 1 has actions reg7 = 0; next;.
Ingress Table 13: 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
step is skipped with a priority-10300 rule if the traffic going out the ECMP route is
reply traffic, and the ECMP route was configured to use symmetric replies. Instead, the
stored values in conntrack is used to choose the destination. The ct_label.ecmp_reply_eth
tells the destination MAC address to which the packet should be sent. The
ct_mark.ecmp_reply_port tells the logical router port on which the packet should be sent.
These values saved to the conntrack fields when the initial ingress traffic is received
over the ECMP route and committed to conntrack. If REGBIT_KNOWN_ECMP_NH is set, the
priority-10300 flows in this stage set the outport, while the eth.dst is set by flows at
the ARP/ND Resolution stage.
This table contains the following logical flows:
• Priority-10550 flow that drops IPv6 Router Solicitation/Advertisement
packets that were not processed in previous tables.
• Priority-10550 flows that drop IGMP and MLD packets with source MAC address
owned by the router. These are used to prevent looping statically forwarded
IGMP and MLD packets for which TTL is not decremented (it is always 1).
• Priority-10500 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-10460 flows that match IGMP and MLD control packets, set 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.
• Priority-10450 flow that matches unregistered IP multicast traffic
decrements TTL 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 = inport;
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 each static route the reg7 == id && is prefixed in logical flow match
portion. For routes with route_table value set a unique non-zero id is used.
For routes within <main> route table (no route table set), this id value is
0.
For each connected route (route to the LRP’s subnet CIDR) the logical flow
match portion has no reg7 == id && prefix to have route to LRP’s subnets in
all routing tables.
• 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, ...);
• A priority-0 logical flow that matches all packets not already handled
(match 1) and drops them (action drop;).
Ingress Table 14: 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 processing is skipped for reply traffic being sent out of an ECMP route if the route
was configured to use symmetric replies.
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;
• A priority-0 logical flow that matches all packets not already handled
(match 1) and drops them (action drop;).
Ingress Table 15: Router policies
This table adds flows for the logical router policies configured on the logical router.
Please see the OVN_Northbound database Logical_Router_Policy table documentation in ovn-nb
for supported actions.
• For each router policy configured on the logical router, a logical flow is
added with specified priority, match and actions.
• If the policy action is reroute with 2 or more nexthops defined, then the
logical flow is added with the following actions:
reg8[0..15] = GID;
reg8[16..31] = select(1,..n);
where GID is the ECMP group id generated by ovn-northd for this policy and n
is the number of nexthops. select action selects one of the nexthop member
id, stores it in the register reg8[16..31] and advances the packet to the
next stage.
• If the policy action is reroute with just one nexhop, then the logical flow
is added with the following actions:
[xx]reg0 = H;
eth.src = E;
outport = P;
reg8[0..15] = 0;
flags.loopback = 1;
next;
where H is the nexthop defined in the router policy, E is the ethernet
address of the logical router port from which the nexthop is reachable and P
is the logical router port from which the nexthop is reachable.
• If a router policy has the option pkt_mark=m set and if the action is not
drop, then the action also includes pkt.mark = m to mark the packet with the
marker m.
Ingress Table 16: ECMP handling for router policies
This table handles the ECMP for the router policies configured with multiple nexthops.
• A priority-150 flow is added to advance the packet to the next stage if the
ECMP group id register reg8[0..15] is 0.
• For each ECMP reroute router policy with multiple nexthops, a priority-100
flow is added for each nexthop H with the match reg8[0..15] == GID &&
reg8[16..31] == M where GID is the router policy group id generated by
ovn-northd and M is the member id of the nexthop H generated by ovn-northd.
The following actions are added to the flow:
[xx]reg0 = H;
eth.src = E;
outport = P
"flags.loopback = 1; "
"next;"
where H is the nexthop defined in the router policy, E is the ethernet
address of the logical router port from which the nexthop is reachable and P
is the logical router port from which the nexthop is reachable.
• A priority-0 logical flow that matches all packets not already handled
(match 1) and drops them (action drop;).
Ingress Table 17: 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.
• Priority-200 flows that match ECMP reply traffic for the routes configured
to use symmetric replies, with actions push(xxreg1); xxreg1 = ct_label;
eth.dst = xxreg1[32..79]; pop(xxreg1); next;. xxreg1 is used here to avoid
masked access to ct_label, to make the flow HW-offloading friendly.
• 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. (Note: the flow is not installed for IPs of
logical switch ports of type virtual, and dynamic MAC binding is used for
those IPs instead, so that virtual parent failover does not depend on
ovn-northd, to achieve better failover performance.) 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. (Note:
the flow is NOT installed for the IP addresses that belong to a neighbor
logical router port if the current router has the
options:dynamic_neigh_routers set to true)
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 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, below two flows are programmed:
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. Note that if the external_ip is not within a subnet on the
owning logical router, then OVN will only create ARP resolution flows if the
options:add_route is set to true. Otherwise, no ARP resolution flows will be
added.
Corresponding to the above flow, a priority-150 flow with the match inport
== P && outport == P && ip4.dst == A has actions drop; to exclude packets
that have gone through DNAT/unSNAT stage but failed to convert the
destination, to avoid loop.
For IPv6 NAT entries, same flows are added, but using the register xxreg0
and field ip6 for the match.
• If the router datapath runs a port with redirect-type set to bridged, for
each distributed NAT rule with IP A in the logical_ip column and logical
port P in the logical_port column of NAT table, a priority-90 flow with the
match outport == Q && ip.src === A && is_chassis_resident(P), where Q is the
distributed logical router port and action get_arp(outport, reg0); next; for
IPv4 and get_nd(outport, xxreg0); next; for IPv6.
• Traffic with IP destination an address owned by the router should be
dropped. Such traffic is normally dropped in ingress table IP Input except
for IPs that are also shared with SNAT rules. However, if there was no
unSNAT operation that happened successfully until this point in the pipeline
and the destination IP of the packet is still a router owned IP, the packets
can be safely dropped.
A priority-2 logical flow with match ip4.dst = {..} matches on traffic
destined to router owned IPv4 addresses which are also SNAT IPs. This flow
has action drop;.
A priority-2 logical flow with match ip6.dst = {..} matches on traffic
destined to router owned IPv6 addresses which are also SNAT IPs. This flow
has action drop;.
A priority-0 logical that flow matches all packets not already handled
(match 1) and drops them (action drop;).
• 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 a distributed gateway LRP with redirect-type set to 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 18: Check packet length
For distributed logical routers or gateway routers with gateway port configured with
options:gateway_mtu to a valid integer value, this table adds a priority-50 logical flow
with the match outport == GW_PORT where GW_PORT is the 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.
If the port is also configured with options:gateway_mtu_bypass then another flow is added,
with priority-55, to bypass the check_pkt_larger flow.
This table adds one priority-0 fallback flow that matches all packets and advances to the
next table.
Ingress Table 19: Handle larger packets
For distributed logical routers or gateway routers with gateway port configured with
options:gateway_mtu to a valid integer value, this table adds the following priority-150
logical flow for each logical router port with the match inport == LRP && outport ==
GW_PORT && REGBIT_PKT_LARGER && !REGBIT_EGRESS_LOOPBACK, where LRP is the logical router
port and GW_PORT is the gateway port and applies the following action for ipv4 and ipv6
respectively:
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;
REGBIT_PKT_LARGER = 0;
next(pipeline=ingress, table=0);
};
icmp6 {
icmp6.type = 2;
icmp6.code = 0;
icmp6.frag_mtu = M;
eth.dst = E;
ip6.dst = ip6.src;
ip6.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER = 0;
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/IPv6 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 20: Gateway Redirect
For distributed logical routers where one or more of the logical router ports specifies a
gateway chassis, this table redirects certain packets to the distributed gateway port
instances on the gateway chassises. This table has the following flows:
• For all the configured load balancing rules that include an IPv4 address
VIP, and a list of IPv4 backend addresses B0, B1 .. Bn defined for the VIP a
priority-200 flow is added that matches ip4 && (ip4.src == B0 || ip4.src ==
B1 || ... || ip4.src == Bn) with an action outport = CR; next; where CR is
the chassisredirect port representing the instance of the logical router
distributed gateway port on the gateway chassis. If the backend IPv4 address
Bx is also configured with L4 port PORT of protocol P, then the match also
includes P.src == PORT. Similar flows are added for IPv6.
• 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 && is_chassis_resident(P), where GW is the distributed gateway
port specified in the NAT rule and P is the NAT logical port. IP traffic
matching the above rule will be managed locally setting reg1 to C and
eth.src to D, where C is NAT external ip and D is NAT external mac.
• For each dnat_and_snat NAT rule with stateless=true and allowed_ext_ips
configured, a priority-75 flow is programmed with match ip4.dst == B and
action outport = CR; next; where B is the NAT rule external IP and CR is the
chassisredirect port representing the instance of the logical router
distributed gateway port on the gateway chassis. Moreover a priority-70 flow
is programmed with same match and action drop;. For each dnat_and_snat NAT
rule with stateless=true and exempted_ext_ips configured, a priority-75 flow
is programmed with match ip4.dst == B and action drop; where B is the NAT
rule external IP. A similar flow is added for IPv6 traffic.
• For each NAT rule in the OVN Northbound database that can be handled in a
distributed manner, a priority-80 logical flow with drop action if the NAT
logical port is a virtual port not claimed by any chassis yet.
• 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 gateway chassis.
• A priority-0 logical flow with match 1 has actions next;.
Ingress Table 21: 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: Check DNAT local
This table checks if the packet needs to be DNATed in the router ingress table lr_in_dnat
after it is SNATed and looped back to the ingress pipeline. This check is done only for
routers configured with distributed gateway ports and NAT entries. This check is done so
that SNAT and DNAT is done in different zones instead of a common zone.
• A priority-0 logical flow with match 1 has actions REGBIT_DST_NAT_IP_LOCAL =
0; next;.
Egress Table 1: 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. This traffic is unDNATed here.
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 1: UNDNAT on Gateway Routers
• For IPv6 Neighbor Discovery or Router Solicitation/Advertisement traffic, a
priority-100 flow with action next;.
• For all IP packets, a priority-50 flow with an action flags.loopback = 1;
ct_dnat;.
Egress Table 1: UNDNAT on Distributed Routers
• 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 gateway 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 next;.
If the NAT rule cannot be handled in a distributed manner, then the
priority-100 flow above is only programmed on the gateway chassis with the
action ct_dnat.
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.
Egress Table 2: Post UNDNAT
• A priority-50 logical flow is added that commits any untracked flows from
the previous table lr_out_undnat for Gateway routers. This flow matches on
ct.new && ip with action ct_commit { } ; next; .
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 3: 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 through conntrack.
Egress Table 3: 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 a load balancer configured to skip snat has been applied to the Gateway
router pipeline, a priority-120 flow matches flags.skip_snat_for_lb == 1 &&
ip with an action next;.
• If the Gateway router in the OVN Northbound database has been configured to
force SNAT a packet (that has been previously load-balanced) using router IP
(i.e options:lb_force_snat_ip=router_ip), then for each logical router port
P attached to the Gateway router, a priority-110 flow matches
flags.force_snat_for_lb == 1 && outport == P
with an action ct_snat(R); where R is the IP configured on the router port.
If R is an IPv4 address then the match will also include ip4 and if it is an
IPv6 address, then the match will also include ip6.
If the logical router port P is configured with multiple IPv4 and multiple
IPv6 addresses, only the first IPv4 and first IPv6 address is considered.
• 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 && (!ct.trk || !ct.rpl) 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 has allowed_ext_ips configured, then there is an additional
match ip4.dst == allowed_ext_ips . Similarly, for IPV6, match would be
ip6.dst == allowed_ext_ips.
• If the NAT rule has exempted_ext_ips set, then there is an additional flow
configured at the priority + 1 of corresponding NAT rule. The flow matches
if destination ip is an exempted_ext_ip and the action is next; . This flow
is used to bypass the ct_snat action for a packet which is destinted to
exempted_ext_ips.
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 3: 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, two flows are
added. The priority P of these flows are calculated based on the mask of A,
with matches having larger masks getting higher priorities.
If the NAT rule cannot be handled in a distributed manner, then the below
flows are only programmed on the gateway chassis increasing flow priority by
128 in order to be run first.
• The first flow is added with the calculated priority P and match ip
&& ip4.src == A && outport == GW, where GW is the logical router
gateway port, with an action ct_snat(B); to SNATed in the common
zone. 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 can be handled in a distributed manner, then there is an
additional action (for both the flows) 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.
If the NAT rule has allowed_ext_ips configured, then there is an additional
match ip4.dst == allowed_ext_ips . Similarly, for IPV6, match would be
ip6.dst == allowed_ext_ips.
If the NAT rule has exempted_ext_ips set, then there is an additional flow
configured at the priority P + 2 of corresponding NAT rule. The flow
matches if destination ip is an exempted_ext_ip and the action is next; .
This flow is used to bypass the ct_snat action for a flow which is destinted
to exempted_ext_ips.
• A priority-0 logical flow with match 1 has actions next;.
Egress Table 4: Post SNAT
Packets reaching this table are processed according to the flows below:
• A priority-0 logical flow that matches all packets not already handled
(match 1) and action next;.
Egress Table 5: Egress Loopback
For distributed logical routers where one of the logical router ports specifies a gateway
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 distributed gateway port corresponding to the NAT rule
(specified or inferred). 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 6: 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;.
• A priority-0 logical flow that matches all packets not already handled
(match 1) and drops them (action drop;).
DROP SAMPLING
As described in the previous section, there are several places where ovn-northd might
decided to drop a packet by explicitly creating a Logical_Flow with the drop; action.
When debug drop-sampling has been cofigured in the OVN Northbound database, the ovn-northd
will replace all the drop; actions with a sample(priority=65535, collector_set=id,
obs_domain=obs_id, obs_point=@cookie) action, where:
• id is the value the debug_drop_collector_set option configured in the OVN
Northbound.
• obs_id has it’s 8 most significant bits equal to the value of the
debug_drop_domain_id option in the OVN Northbound and it’s 24 least
significant bits equal to the datapath’s tunnel key.