1 <?xml version="1.0" encoding="utf-8"?>
2 <manpage program="ovn-northd" section="8" title="ovn-northd">
4 <p>ovn-northd -- Open Virtual Network central control daemon</p>
7 <p><code>ovn-northd</code> [<var>options</var>]</p>
11 <code>ovn-northd</code> is a centralized daemon responsible for
12 translating the high-level OVN configuration into logical
13 configuration consumable by daemons such as
14 <code>ovn-controller</code>. It translates the logical network
15 configuration in terms of conventional network concepts, taken
16 from the OVN Northbound Database (see <code>ovn-nb</code>(5)),
17 into logical datapath flows in the OVN Southbound Database (see
18 <code>ovn-sb</code>(5)) below it.
21 <h1>Configuration</h1>
23 <code>ovn-northd</code> requires a connection to the Northbound
24 and Southbound databases. The defaults are <code>ovnnb_db.sock</code>
25 and <code>ovnsb_db.sock</code> respectively
26 in the local Open vSwitch's "run" directory. This may be
27 overridden with the following commands:
32 <code>--ovnnb-db=<var>database</var></code>
35 The database containing the OVN Northbound Database.
40 <code>--ovnsb-db=<var>database</var></code>
43 The database containing the OVN Southbound Database.
48 The <var>database</var> argument must take one of the following forms:
53 <code>ssl:<var>ip</var>:<var>port</var></code>
56 The specified SSL <var>port</var> on the host at the given
57 <var>ip</var>, which must be expressed as an IP address (not a DNS
58 name) in IPv4 or IPv6 address format. If <var>ip</var> is an IPv6
59 address, then wrap <var>ip</var> with square brackets, e.g.:
60 <code>ssl:[::1]:6640</code>. The <code>--private-key</code>,
61 <code>--certificate</code>, and <code>--ca-cert</code> options are
62 mandatory when this form is used.
67 <code>tcp:<var>ip</var>:<var>port</var></code>
70 Connect to the given TCP <var>port</var> on <var>ip</var>, where
71 <var>ip</var> can be IPv4 or IPv6 address. If <var>ip</var> is an
72 IPv6 address, then wrap <var>ip</var> with square brackets, e.g.:
73 <code>tcp:[::1]:6640</code>.
78 <code>unix:<var>file</var></code>
81 On POSIX, connect to the Unix domain server socket named
85 On Windows, connect to a localhost TCP port whose value is written
91 <h1>Runtime Management Commands</h1>
93 <code>ovs-appctl</code> can send commands to a running
94 <code>ovn-northd</code> process. The currently supported commands
97 <dt><code>exit</code></dt>
99 Causes <code>ovn-northd</code> to gracefully terminate.
104 <h1>Logical Flow Table Structure</h1>
107 One of the main purposes of <code>ovn-northd</code> is to populate the
108 <code>Logical_Flow</code> table in the <code>OVN_Southbound</code>
109 database. This section describes how <code>ovn-northd</code> does this
110 for switch and router logical datapaths.
113 <h2>Logical Switch Datapaths</h2>
115 <h3>Ingress Table 0: Admission Control and Ingress Port Security - L2</h3>
118 Ingress table 0 contains these logical flows:
123 Priority 100 flows to drop packets with VLAN tags or multicast Ethernet
128 Priority 50 flows that implement ingress port security for each enabled
129 logical port. For logical ports on which port security is enabled,
130 these match the <code>inport</code> and the valid <code>eth.src</code>
131 address(es) and advance only those packets to the next flow table. For
132 logical ports on which port security is not enabled, these advance all
133 packets that match the <code>inport</code>.
138 There are no flows for disabled logical ports because the default-drop
139 behavior of logical flow tables causes packets that ingress from them to
143 <h3>Ingress Table 1: Ingress Port Security - IP</h3>
146 Ingress table 1 contains these logical flows:
152 For each element in the port security set having one or more IPv4 or
153 IPv6 addresses (or both),
158 Priority 90 flow to allow IPv4 traffic if it has IPv4 addresses
159 which match the <code>inport</code>, valid <code>eth.src</code>
160 and valid <code>ip4.src</code> address(es).
164 Priority 90 flow to allow IPv4 DHCP discovery traffic if it has a
165 valid <code>eth.src</code>. This is necessary since DHCP discovery
166 messages are sent from the unspecified IPv4 address (0.0.0.0) since
167 the IPv4 address has not yet been assigned.
171 Priority 90 flow to allow IPv6 traffic if it has IPv6 addresses
172 which match the <code>inport</code>, valid <code>eth.src</code> and
173 valid <code>ip6.src</code> address(es).
177 Priority 90 flow to allow IPv6 DAD (Duplicate Address Detection)
178 traffic if it has a valid <code>eth.src</code>. This is is
179 necessary since DAD include requires joining an multicast group and
180 sending neighbor solicitations for the newly assigned address. Since
181 no address is yet assigned, these are sent from the unspecified
186 Priority 80 flow to drop IP (both IPv4 and IPv6) traffic which
187 match the <code>inport</code> and valid <code>eth.src</code>.
193 One priority-0 fallback flow that matches all packets and advances to
198 <h3>Ingress Table 2: Ingress Port Security - Neighbor discovery</h3>
201 Ingress table 2 contains these logical flows:
207 For each element in the port security set,
212 Priority 90 flow to allow ARP traffic which match the
213 <code>inport</code> and valid <code>eth.src</code> and
214 <code>arp.sha</code>. If the element has one or more
215 IPv4 addresses, then it also matches the valid
216 <code>arp.spa</code>.
220 Priority 90 flow to allow IPv6 Neighbor Solicitation and
221 Advertisement traffic which match the <code>inport</code>,
222 valid <code>eth.src</code> and
223 <code>nd.sll</code>/<code>nd.tll</code>.
224 If the element has one or more IPv6 addresses, then it also
225 matches the valid <code>nd.target</code> address(es) for Neighbor
226 Advertisement traffic.
230 Priority 80 flow to drop ARP and IPv6 Neighbor Solicitation and
231 Advertisement traffic which match the <code>inport</code> and
232 valid <code>eth.src</code>.
238 One priority-0 fallback flow that matches all packets and advances to
243 <h3>Ingress Table 3: <code>from-lport</code> Pre-ACLs</h3>
246 This table prepares flows for possible stateful ACL processing in
247 ingress table <code>ACLs</code>. It contains a priority-0 flow that
248 simply moves traffic to the next table. If stateful ACLs are used in the
249 logical datapath, a priority-100 flow is added that sets a hint
250 (with <code>reg0[0] = 1; next;</code>) for table
251 <code>Pre-stateful</code> to send IP packets to the connection tracker
252 before eventually advancing to ingress table <code>ACLs</code>.
255 <h3>Ingress Table 4: Pre-LB</h3>
258 This table prepares flows for possible stateful load balancing processing
259 in ingress table <code>LB</code> and <code>Stateful</code>. It contains
260 a priority-0 flow that simply moves traffic to the next table. If load
261 balancing rules with virtual IP addresses (and ports) are configured in
262 <code>OVN_Northbound</code> database for a logical datapath, a
263 priority-100 flow is added for each configured virtual IP address
264 <var>VIP</var> with a match <code>ip && ip4.dst == <var>VIP</var>
265 </code> that sets an action <code>reg0[0] = 1; next;</code> to act as a
266 hint for table <code>Pre-stateful</code> to send IP packets to the
267 connection tracker for packet de-fragmentation before eventually
268 advancing to ingress table <code>LB</code>.
271 <h3>Ingress Table 5: Pre-stateful</h3>
274 This table prepares flows for all possible stateful processing
275 in next tables. It contains a priority-0 flow that simply moves
276 traffic to the next table. A priority-100 flow sends the packets to
277 connection tracker based on a hint provided by the previous tables
278 (with a match for <code>reg0[0] == 1</code>) by using the
279 <code>ct_next;</code> action.
282 <h3>Ingress table 6: <code>from-lport</code> ACLs</h3>
285 Logical flows in this table closely reproduce those in the
286 <code>ACL</code> table in the <code>OVN_Northbound</code> database
287 for the <code>from-lport</code> direction. <code>allow</code>
288 ACLs translate into logical flows with the <code>next;</code>
289 action, <code>allow-related</code> ACLs translate into logical
290 flows with the <code>reg0[1] = 1; next;</code> actions (which acts
291 as a hint for the next tables to commit the connection to conntrack),
292 other ACLs translate to <code>drop;</code>. The <code>priority</code>
293 values from the <code>ACL</code> table have a limited range and have 1000
294 added to them to leave room for OVN default flows at both higher
295 and lower priorities.
299 This table also contains a priority 0 flow with action
300 <code>next;</code>, so that ACLs allow packets by default. If the
301 logical datapath has a statetful ACL, the following flows will
307 A priority-1 flow that sets the hint to commit IP traffic to the
308 connection tracker (with action <code>reg0[1] = 1; next;</code>). This
309 is needed for the default allow policy because, while the initiator's
310 direction may not have any stateful rules, the server's may and then
311 its return traffic would not be known and marked as invalid.
315 A priority-65535 flow that allows any traffic that has been
316 committed to the connection tracker (i.e., established flows).
320 A priority-65535 flow that allows any traffic that is considered
321 related to a committed flow in the connection tracker (e.g., an
322 ICMP Port Unreachable from a non-listening UDP port).
326 A priority-65535 flow that drops all traffic marked by the
327 connection tracker as invalid.
331 <h3>Ingress Table 7: LB</h3>
334 It contains a priority-0 flow that simply moves traffic to the next
335 table. For established connections a priority 100 flow matches on
336 <code>ct.est && !ct.rel && !ct.new &&
337 !ct.inv</code> and sets an action <code>reg0[2] = 1; next;</code> to act
338 as a hint for table <code>Stateful</code> to send packets through
339 connection tracker to NAT the packets. (The packet will automatically
340 get DNATed to the same IP address as the first packet in that
344 <h3>Ingress Table 8: Stateful</h3>
348 For all the configured load balancing rules in
349 <code>OVN_Northbound</code> database that includes a L4 port
350 <var>PORT</var> of protocol <var>P</var> and IPv4 address
351 <var>VIP</var>, a priority-120 flow that matches on
352 <code>ct.new && ip && ip4.dst == <var>VIP
353 </var>&& <var>P</var> && <var>P</var>.dst == <var>PORT
354 </var></code> with an action of <code>ct_lb(<var>args</var>)</code>,
355 where <var>args</var> contains comma separated IPv4 addresses (and
356 optional port numbers) to load balance to.
359 For all the configured load balancing rules in
360 <code>OVN_Northbound</code> database that includes just an IP address
361 <var>VIP</var> to match on, a priority-110 flow that matches on
362 <code>ct.new && ip && ip4.dst == <var>VIP</var></code>
363 with an action of <code>ct_lb(<var>args</var>)</code>, where
364 <var>args</var> contains comma separated IPv4 addresses.
367 A priority-100 flow commits packets to connection tracker using
368 <code>ct_commit; next;</code> action based on a hint provided by
369 the previous tables (with a match for <code>reg0[1] == 1</code>).
372 A priority-100 flow sends the packets to connection tracker using
373 <code>ct_lb;</code> as the action based on a hint provided by the
374 previous tables (with a match for <code>reg0[2] == 1</code>).
377 A priority-0 flow that simply moves traffic to the next table.
381 <h3>Ingress Table 9: ARP responder</h3>
384 This table implements ARP responder for known IPs. It contains these
390 Priority-100 flows to skip ARP responder if inport is of type
391 <code>localnet</code>, and advances directly to the next table.
396 Priority-50 flows that matches ARP requests to each known IP address
397 <var>A</var> of logical port <var>P</var>, and respond with ARP
398 replies directly with corresponding Ethernet address <var>E</var>:
403 eth.src = <var>E</var>;
404 arp.op = 2; /* ARP reply. */
406 arp.sha = <var>E</var>;
408 arp.spa = <var>A</var>;
409 outport = <var>P</var>;
410 inport = ""; /* Allow sending out inport. */
415 These flows are omitted for logical ports (other than router ports)
421 One priority-0 fallback flow that matches all packets and advances to
426 <h3>Ingress Table 10: Destination Lookup</h3>
429 This table implements switching behavior. It contains these logical
435 A priority-100 flow that outputs all packets with an Ethernet broadcast
436 or multicast <code>eth.dst</code> to the <code>MC_FLOOD</code>
437 multicast group, which <code>ovn-northd</code> populates with all
438 enabled logical ports.
442 One priority-50 flow that matches each known Ethernet address against
443 <code>eth.dst</code> and outputs the packet to the single associated
448 One priority-0 fallback flow that matches all packets and outputs them
449 to the <code>MC_UNKNOWN</code> multicast group, which
450 <code>ovn-northd</code> populates with all enabled logical ports that
451 accept unknown destination packets. As a small optimization, if no
452 logical ports accept unknown destination packets,
453 <code>ovn-northd</code> omits this multicast group and logical flow.
457 <h3>Egress Table 0: Pre-LB</h3>
460 This table is similar to ingress table <code>Pre-LB</code>. It
461 contains a priority-0 flow that simply moves traffic to the next table.
462 If any load balancing rules exist for the datapath, a priority-100 flow
463 is added with a match of <code>ip</code> and action of <code>reg0[0] = 1;
464 next;</code> to act as a hint for table <code>Pre-stateful</code> to
465 send IP packets to the connection tracker for packet de-fragmentation.
468 <h3>Egress Table 1: <code>to-lport</code> Pre-ACLs</h3>
471 This is similar to ingress table <code>Pre-ACLs</code> except for
472 <code>to-lport</code> traffic.
475 <h3>Egress Table 2: Pre-stateful</h3>
478 This is similar to ingress table <code>Pre-stateful</code>.
481 <h3>Egress Table 3: LB</h3>
483 This is similar to ingress table <code>LB</code>.
486 <h3>Egress Table 4: <code>to-lport</code> ACLs</h3>
489 This is similar to ingress table <code>ACLs</code> except for
490 <code>to-lport</code> ACLs.
493 <h3>Egress Table 5: Stateful</h3>
496 This is similar to ingress table <code>Stateful</code> except that
497 there are no rules added for load balancing new connections.
500 <h3>Egress Table 6: Egress Port Security - IP</h3>
503 This is similar to the port security logic in table
504 <code>Ingress Port Security - IP</code> except that <code>outport</code>,
505 <code>eth.dst</code>, <code>ip4.dst</code> and <code>ip6.dst</code>
506 are checked instead of <code>inport</code>, <code>eth.src</code>,
507 <code>ip4.src</code> and <code>ip6.src</code>
510 <h3>Egress Table 7: Egress Port Security - L2</h3>
513 This is similar to the ingress port security logic in ingress table
514 <code>Admission Control and Ingress Port Security - L2</code>,
515 but with important differences. Most obviously, <code>outport</code> and
516 <code>eth.dst</code> are checked instead of <code>inport</code> and
517 <code>eth.src</code>. Second, packets directed to broadcast or multicast
518 <code>eth.dst</code> are always accepted instead of being subject to the
519 port security rules; this is implemented through a priority-100 flow that
520 matches on <code>eth.mcast</code> with action <code>output;</code>.
521 Finally, to ensure that even broadcast and multicast packets are not
522 delivered to disabled logical ports, a priority-150 flow for each
523 disabled logical <code>outport</code> overrides the priority-100 flow
524 with a <code>drop;</code> action.
527 <h2>Logical Router Datapaths</h2>
530 Logical router datapaths will only exist for <ref table="Logical_Router"
531 db="OVN_Northbound"/> rows in the <ref db="OVN_Northbound"/> database
532 that do not have <ref column="enabled" table="Logical_Router"
533 db="OVN_Northbound"/> set to <code>false</code>
536 <h3>Ingress Table 0: L2 Admission Control</h3>
539 This table drops packets that the router shouldn't see at all based on
540 their Ethernet headers. It contains the following flows:
545 Priority-100 flows to drop packets with VLAN tags or multicast Ethernet
550 For each enabled router port <var>P</var> with Ethernet address
551 <var>E</var>, a priority-50 flow that matches <code>inport ==
552 <var>P</var> && (eth.mcast || eth.dst ==
553 <var>E</var></code>), with action <code>next;</code>.
558 Other packets are implicitly dropped.
561 <h3>Ingress Table 1: IP Input</h3>
564 This table is the core of the logical router datapath functionality. It
565 contains the following flows to implement very basic IP host
572 L3 admission control: A priority-100 flow drops packets that match
573 any of the following:
578 <code>ip4.src[28..31] == 0xe</code> (multicast source)
581 <code>ip4.src == 255.255.255.255</code> (broadcast source)
584 <code>ip4.src == 127.0.0.0/8 || ip4.dst == 127.0.0.0/8</code>
585 (localhost source or destination)
588 <code>ip4.src == 0.0.0.0/8 || ip4.dst == 0.0.0.0/8</code> (zero
589 network source or destination)
592 <code>ip4.src</code> is any IP address owned by the router.
595 <code>ip4.src</code> is the broadcast address of any IP network
603 ICMP echo reply. These flows reply to ICMP echo requests received
604 for the router's IP address. Let <var>A</var> be an IP address
605 owned by a router port. Then, for each <var>A</var>, a priority-90
606 flow matches on <code>ip4.dst == <var>A</var></code> and <code>
607 icmp4.type == 8 && icmp4.code == 0</code> (ICMP echo
608 request). The port of the router that receives the echo request
609 does not matter. Also, the ip.ttl of the echo request packet is not
610 checked, so it complies with RFC 1812, section 4.2.2.9. These flows
611 use the following actions:
615 ip4.dst <-> ip4.src;
618 inport = ""; /* Allow sending out inport. */
625 Reply to ARP requests.
629 These flows reply to ARP requests for the router's own IP address.
630 For each router port <var>P</var> that owns IP address <var>A</var>
631 and Ethernet address <var>E</var>, a priority-90 flow matches
632 <code>inport == <var>P</var> && arp.op == 1 &&
633 arp.tpa == <var>A</var></code> (ARP request) with the following
639 eth.src = <var>E</var>;
640 arp.op = 2; /* ARP reply. */
642 arp.sha = <var>E</var>;
644 arp.spa = <var>A</var>;
645 outport = <var>P</var>;
646 inport = ""; /* Allow sending out inport. */
653 These flows reply to ARP requests for the virtual IP addresses
654 configured in the router for DNAT. For a configured DNAT IP address
655 <var>A</var>, for each router port <var>P</var> with Ethernet
656 address <var>E</var>, a priority-90 flow matches
657 <code>inport == <var>P</var> && arp.op == 1 &&
658 arp.tpa == <var>A</var></code> (ARP request)
659 with the following actions:
664 eth.src = <var>E</var>;
665 arp.op = 2; /* ARP reply. */
667 arp.sha = <var>E</var>;
669 arp.spa = <var>A</var>;
670 outport = <var>P</var>;
671 inport = ""; /* Allow sending out inport. */
677 ARP reply handling. These flows use ARP replies to populate the
678 logical router's ARP table. A priority-90 flow with match <code>arp.op
679 == 2</code> has actions <code>put_arp(inport, arp.spa,
685 UDP port unreachable. Priority-80 flows generate ICMP port
686 unreachable messages in reply to UDP datagrams directed to the
687 router's IP address. The logical router doesn't accept any UDP
688 traffic so it always generates such a reply.
692 These flows should not match IP fragments with nonzero offset.
696 Details TBD. Not yet implemented.
702 TCP reset. Priority-80 flows generate TCP reset messages in reply to
703 TCP datagrams directed to the router's IP address. The logical
704 router doesn't accept any TCP traffic so it always generates such a
709 These flows should not match IP fragments with nonzero offset.
713 Details TBD. Not yet implemented.
719 Protocol unreachable. Priority-70 flows generate ICMP protocol
720 unreachable messages in reply to packets directed to the router's IP
721 address on IP protocols other than UDP, TCP, and ICMP.
725 These flows should not match IP fragments with nonzero offset.
729 Details TBD. Not yet implemented.
734 Drop other IP traffic to this router. These flows drop any other
735 traffic destined to an IP address of this router that is not already
736 handled by one of the flows above, which amounts to ICMP (other than
737 echo requests) and fragments with nonzero offsets. For each IP address
738 <var>A</var> owned by the router, a priority-60 flow matches
739 <code>ip4.dst == <var>A</var></code> and drops the traffic. An
740 exception is made and the above flow is not added if the router
741 port's own IP address is used to SNAT packets passing through that
747 The flows above handle all of the traffic that might be directed to the
748 router itself. The following flows (with lower priorities) handle the
749 remaining traffic, potentially for forwarding:
754 Drop Ethernet local broadcast. A priority-50 flow with match
755 <code>eth.bcast</code> drops traffic destined to the local Ethernet
756 broadcast address. By definition this traffic should not be forwarded.
761 ICMP time exceeded. For each router port <var>P</var>, whose IP
762 address is <var>A</var>, a priority-40 flow with match <code>inport
763 == <var>P</var> && ip.ttl == {0, 1} &&
764 !ip.later_frag</code> matches packets whose TTL has expired, with the
765 following actions to send an ICMP time exceeded reply:
770 icmp4.type = 11; /* Time exceeded. */
771 icmp4.code = 0; /* TTL exceeded in transit. */
773 ip4.src = <var>A</var>;
785 TTL discard. A priority-30 flow with match <code>ip.ttl == {0,
786 1}</code> and actions <code>drop;</code> drops other packets whose TTL
787 has expired, that should not receive a ICMP error reply (i.e. fragments
788 with nonzero offset).
792 Next table. A priority-0 flows match all packets that aren't already
793 handled and uses actions <code>next;</code> to feed them to the ingress
798 <h3>Ingress Table 2: UNSNAT</h3>
801 This is for already established connections' reverse traffic.
802 i.e., SNAT has already been done in egress pipeline and now the
803 packet has entered the ingress pipeline as part of a reply. It is
810 For each configuration in the OVN Northbound database, that asks
811 to change the source IP address of a packet from <var>A</var> to
812 <var>B</var>, a priority-100 flow matches <code>ip &&
813 ip4.dst == <var>B</var></code> with an action
814 <code>ct_snat; next;</code>.
818 A priority-0 logical flow with match <code>1</code> has actions
824 <h3>Ingress Table 3: DNAT</h3>
827 Packets enter the pipeline with destination IP address that needs to
828 be DNATted from a virtual IP address to a real IP address. Packets
829 in the reverse direction needs to be unDNATed.
834 For each configuration in the OVN Northbound database, that asks
835 to change the destination IP address of a packet from <var>A</var> to
836 <var>B</var>, a priority-100 flow matches <code>ip &&
837 ip4.dst == <var>A</var></code> with an action <code>inport = "";
838 ct_dnat(<var>B</var>);</code>.
842 For all IP packets of a Gateway router, a priority-50 flow with an
843 action <code>inport = ""; ct_dnat;</code>.
847 A priority-0 logical flow with match <code>1</code> has actions
853 <h3>Ingress Table 4: IP Routing</h3>
856 A packet that arrives at this table is an IP packet that should be routed
857 to the address in <code>ip4.dst</code>. This table implements IP
858 routing, setting <code>reg0</code> to the next-hop IP address (leaving
859 <code>ip4.dst</code>, the packet's final destination, unchanged) and
860 advances to the next table for ARP resolution. It also sets
861 <code>reg1</code> to the IP address owned by the selected router port
862 (which is used later in table 6 as the IP source address for an ARP
867 This table contains the following logical flows:
873 Routing table. For each route to IPv4 network <var>N</var> with
874 netmask <var>M</var>, on router port <var>P</var> with IP address
875 <var>A</var> and Ethernet
876 address <var>E</var>, a logical flow with match <code>ip4.dst ==
877 <var>N</var>/<var>M</var></code>, whose priority is the number of
878 1-bits in <var>M</var>, has the following actions:
885 eth.src = <var>E</var>;
886 outport = <var>P</var>;
887 inport = ""; /* Allow sending out inport. */
892 (Ingress table 1 already verified that <code>ip.ttl--;</code> will
893 not yield a TTL exceeded error.)
897 If the route has a gateway, <var>G</var> is the gateway IP address.
898 Instead, if the route is from a configured static route, <var>G</var>
899 is the next hop IP address. Else it is <code>ip4.dst</code>.
905 Destination unreachable. For each router port <var>P</var>, which
906 owns IP address <var>A</var>, a priority-0 logical flow with match
907 <code>in_port == <var>P</var> && !ip.later_frag &&
908 !icmp</code> has the following actions:
913 icmp4.type = 3; /* Destination unreachable. */
914 icmp4.code = 0; /* Network unreachable. */
916 ip4.src = <var>A</var>;
923 (The <code>!icmp</code> check prevents recursion if the destination
924 unreachable message itself cannot be routed.)
928 These flows are omitted if the logical router has a default route,
929 that is, a route with netmask 0.0.0.0.
934 <h3>Ingress Table 5: ARP Resolution</h3>
937 Any packet that reaches this table is an IP packet whose next-hop IP
938 address is in <code>reg0</code>. (<code>ip4.dst</code> is the final
939 destination.) This table resolves the IP address in <code>reg0</code>
940 into an output port in <code>outport</code> and an Ethernet address in
941 <code>eth.dst</code>, using the following flows:
947 Static MAC bindings. MAC bindings can be known statically based on
948 data in the <code>OVN_Northbound</code> database. For router ports
949 connected to logical switches, MAC bindings can be known statically
950 from the <code>addresses</code> column in the
951 <code>Logical_Switch_Port</code> table. For router ports
952 connected to other logical routers, MAC bindings can be known
953 statically from the <code>mac</code> and <code>networks</code>
954 column in the <code>Logical_Router_Port</code> table.
958 For each IP address <var>A</var> whose host is known to have Ethernet
959 address <var>E</var> on router port <var>P</var>, a priority-100 flow
960 with match <code>outport === <var>P</var> && reg0 ==
961 <var>A</var></code> has actions <code>eth.dst = <var>E</var>;
966 For each logical router port with an IP address <var>A</var> and
967 a mac address of <var>E</var> that is reachable via a different
968 logical router port <var>P</var>, a priority-100 flow with
969 match <code>outport === <var>P</var> && reg0 ==
970 <var>A</var></code> has actions <code>eth.dst = <var>E</var>;
977 Dynamic MAC bindings. This flows resolves MAC-to-IP bindings that
978 have become known dynamically through ARP. (The next table will
979 issue an ARP request for cases where the binding is not yet known.)
983 A priority-0 logical flow with match <code>1</code> has actions
984 <code>get_arp(outport, reg0); next;</code>.
989 <h3>Ingress Table 6: ARP Request</h3>
992 In the common case where the Ethernet destination has been resolved, this
993 table outputs the packet. Otherwise, it composes and sends an ARP
994 request. It holds the following flows:
1000 Unknown MAC address. A priority-100 flow with match <code>eth.dst ==
1001 00:00:00:00:00:00</code> has the following actions:
1006 eth.dst = ff:ff:ff:ff:ff:ff;
1008 arp.op = 1; /* ARP request. */
1014 (Ingress table 4 initialized <code>reg1</code> with the IP address
1015 owned by <code>outport</code>.)
1019 The IP packet that triggers the ARP request is dropped.
1024 Known MAC address. A priority-0 flow with match <code>1</code> has
1025 actions <code>output;</code>.
1029 <h3>Egress Table 0: SNAT</h3>
1032 Packets that are configured to be SNATed get their source IP address
1033 changed based on the configuration in the OVN Northbound database.
1038 For each configuration in the OVN Northbound database, that asks
1039 to change the source IP address of a packet from an IP address of
1040 <var>A</var> or to change the source IP address of a packet that
1041 belongs to network <var>A</var> to <var>B</var>, a flow matches
1042 <code>ip && ip4.src == <var>A</var></code> with an action
1043 <code>ct_snat(<var>B</var>);</code>. The priority of the flow
1044 is calculated based on the mask of <var>A</var>, with matches
1045 having larger masks getting higher priorities.
1048 A priority-0 logical flow with match <code>1</code> has actions
1054 <h3>Egress Table 1: Delivery</h3>
1057 Packets that reach this table are ready for delivery. It contains
1058 priority-100 logical flows that match packets on each enabled logical
1059 router port, with action <code>output;</code>.