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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 default is <code>db.sock</code>
25 in the local Open vSwitch's "run" directory. This may be
26 overridden with the following commands:
31 <code>--ovnnb-db=<var>database</var></code>
34 The database containing the OVN Northbound Database.
39 <code>--ovsnb-db=<var>database</var></code>
42 The database containing the OVN Southbound Database.
47 The <var>database</var> argument must take one of the following forms:
52 <code>ssl:<var>ip</var>:<var>port</var></code>
55 The specified SSL <var>port</var> on the host at the given
56 <var>ip</var>, which must be expressed as an IP address (not a DNS
57 name) in IPv4 or IPv6 address format. If <var>ip</var> is an IPv6
58 address, then wrap <var>ip</var> with square brackets, e.g.:
59 <code>ssl:[::1]:6640</code>. The <code>--private-key</code>,
60 <code>--certificate</code>, and <code>--ca-cert</code> options are
61 mandatory when this form is used.
66 <code>tcp:<var>ip</var>:<var>port</var></code>
69 Connect to the given TCP <var>port</var> on <var>ip</var>, where
70 <var>ip</var> can be IPv4 or IPv6 address. If <var>ip</var> is an
71 IPv6 address, then wrap <var>ip</var> with square brackets, e.g.:
72 <code>tcp:[::1]:6640</code>.
77 <code>unix:<var>file</var></code>
80 On POSIX, connect to the Unix domain server socket named
84 On Windows, connect to a localhost TCP port whose value is written
90 <h1>Runtime Management Commands</h1>
92 <code>ovs-appctl</code> can send commands to a running
93 <code>ovn-northd</code> process. The currently supported commands
96 <dt><code>exit</code></dt>
98 Causes <code>ovn-northd</code> to gracefully terminate.
103 <h1>Logical Flow Table Structure</h1>
106 One of the main purposes of <code>ovn-northd</code> is to populate the
107 <code>Logical_Flow</code> table in the <code>OVN_Southbound</code>
108 database. This section describes how <code>ovn-northd</code> does this
109 for switch and router logical datapaths.
112 <h2>Logical Switch Datapaths</h2>
114 <h3>Ingress Table 0: Admission Control and Ingress Port Security</h3>
117 Ingress table 0 contains these logical flows:
122 Priority 100 flows to drop packets with VLAN tags or multicast Ethernet
127 Priority 50 flows that implement ingress port security for each enabled
128 logical port. For logical ports on which port security is enabled,
129 these match the <code>inport</code> and the valid <code>eth.src</code>
130 address(es) and advance only those packets to the next flow table. For
131 logical ports on which port security is not enabled, these advance all
132 packets that match the <code>inport</code>.
137 There are no flows for disabled logical ports because the default-drop
138 behavior of logical flow tables causes packets that ingress from them to
142 <h3>Ingress Table 1: <code>from-lport</code> Pre-ACLs</h3>
145 Ingress table 1 prepares flows for possible stateful ACL processing
146 in table 2. It contains a priority-0 flow that simply moves
147 traffic to table 2. If stateful ACLs are used in the logical
148 datapath, a priority-100 flow is added that sends IP packets to
149 the connection tracker before advancing to table 2.
152 <h3>Ingress table 2: <code>from-lport</code> ACLs</h3>
155 Logical flows in this table closely reproduce those in the
156 <code>ACL</code> table in the <code>OVN_Northbound</code> database
157 for the <code>from-lport</code> direction. <code>allow</code>
158 ACLs translate into logical flows with the <code>next;</code>
159 action, <code>allow-related</code> ACLs translate into logical
160 flows with the <code>ct_next;</code> action, other ACLs translate
161 to <code>drop;</code>. The <code>priority</code> values from the
162 <code>ACL</code> table are used directly.
166 Ingress table 2 also contains a priority 0 flow with action
167 <code>next;</code>, so that ACLs allow packets by default. If the
168 logical datapath has a statetful ACL, the following flows will
174 A priority-1 flow to commit IP traffic to the connection
175 tracker. This is needed for the default allow policy because,
176 while the initiater's direction may not have any stateful rules,
177 the server's may and then its return traffic would not be known
178 and marked as invalid.
182 A priority-65535 flow that allows any traffic that has been
183 committed to the connection tracker (i.e., established flows).
187 A priority-65535 flow that allows any traffic that is considered
188 related to a committed flow in the connection tracker (e.g., an
189 ICMP Port Unreachable from a non-listening UDP port).
193 A priority-65535 flow that drops all traffic marked by the
194 connection tracker as invalid.
198 <h3>Ingress Table 3: Destination Lookup</h3>
201 This table implements switching behavior. It contains these logical
207 A priority-100 flow that outputs all packets with an Ethernet broadcast
208 or multicast <code>eth.dst</code> to the <code>MC_FLOOD</code>
209 multicast group, which <code>ovn-northd</code> populates with all
210 enabled logical ports.
214 One priority-50 flow that matches each known Ethernet address against
215 <code>eth.dst</code> and outputs the packet to the single associated
220 One priority-0 fallback flow that matches all packets and outputs them
221 to the <code>MC_UNKNOWN</code> multicast group, which
222 <code>ovn-northd</code> populates with all enabled logical ports that
223 accept unknown destination packets. As a small optimization, if no
224 logical ports accept unknown destination packets,
225 <code>ovn-northd</code> omits this multicast group and logical flow.
229 <h3>Egress Table 0: <code>to-lport</code> Pre-ACLs</h3>
232 This is similar to ingress table 1 except for <code>to-lport</code>
236 <h3>Egress Table 1: <code>to-lport</code> ACLs</h3>
239 This is similar to ingress table 2 except for <code>to-lport</code> ACLs.
242 <h3>Egress Table 2: Egress Port Security</h3>
245 This is similar to the ingress port security logic in ingress table 0,
246 but with important differences. Most obviously, <code>outport</code> and
247 <code>eth.dst</code> are checked instead of <code>inport</code> and
248 <code>eth.src</code>. Second, packets directed to broadcast or multicast
249 <code>eth.dst</code> are always accepted instead of being subject to the
250 port security rules; this is implemented through a priority-100 flow that
251 matches on <code>eth.mcast</code> with action <code>output;</code>.
252 Finally, to ensure that even broadcast and multicast packets are not
253 delivered to disabled logical ports, a priority-150 flow for each
254 disabled logical <code>outport</code> overrides the priority-100 flow
255 with a <code>drop;</code> action.
258 <h2>Logical Router Datapaths</h2>
260 <h3>Ingress Table 0: L2 Admission Control</h3>
263 This table drops packets that the router shouldn't see at all based on
264 their Ethernet headers. It contains the following flows:
269 Priority-100 flows to drop packets with VLAN tags or multicast Ethernet
274 For each enabled router port <var>P</var> with Ethernet address
275 <var>E</var>, a priority-50 flow that matches <code>inport ==
276 <var>P</var> && (eth.mcast || eth.dst ==
277 <var>E</var></code>), with action <code>next;</code>.
282 Other packets are implicitly dropped.
285 <h3>Ingress Table 1: IP Input</h3>
288 This table is the core of the logical router datapath functionality. It
289 contains the following flows to implement very basic IP host
296 L3 admission control: A priority-100 flow drops packets that match
297 any of the following:
302 <code>ip4.src[28..31] == 0xe</code> (multicast source)
305 <code>ip4.src == 255.255.255.255</code> (broadcast source)
308 <code>ip4.src == 127.0.0.0/8 || ip4.dst == 127.0.0.0/8</code>
309 (localhost source or destination)
312 <code>ip4.src == 0.0.0.0/8 || ip4.dst == 0.0.0.0/8</code> (zero
313 network source or destination)
316 <code>ip4.src</code> is any IP address owned by the router.
319 <code>ip4.src</code> is the broadcast address of any IP network
327 ICMP echo reply. These flows reply to ICMP echo requests received
328 for the router's IP address. Let <var>A</var> be an IP address or
329 broadcast address owned by a router port. Then, for each
330 <var>A</var>, a priority-90 flow matches on <code>ip4.dst ==
331 <var>A</var></code> and <code>icmp4.type == 8 && icmp4.code
332 == 0</code> (ICMP echo request). These flows use the following
333 actions where, if <var>A</var> is unicast, then <var>S</var> is
334 <var>A</var>, and if <var>A</var> is broadcast, <var>S</var> is the
335 router's IP address in <var>A</var>'s network:
340 ip4.src = <var>S</var>;
347 Similar flows match on <code>ip4.dst == 255.255.255.255</code> and
348 each individual <code>inport</code>, and use the same actions in
349 which <var>S</var> is a function of <code>inport</code>.
359 ARP reply. These flows reply to ARP requests for the router's own IP
360 address. For each router port <var>P</var> that owns IP address
361 <var>A</var> and Ethernet address <var>E</var>, a priority-90 flow
362 matches <code>inport == <var>P</var> && arp.tpa ==
363 <var>A</var> && arp.op == 1</code> (ARP request) with the
369 eth.src = <var>E</var>;
370 arp.op = 2; /* ARP reply. */
372 arp.sha = <var>E</var>;
374 arp.spa = <var>A</var>;
375 outport = <var>P</var>;
376 inport = \"\"; /* Allow sending out inport. */
383 UDP port unreachable. Priority-80 flows generate ICMP port
384 unreachable messages in reply to UDP datagrams directed to the
385 router's IP address. The logical router doesn't accept any UDP
386 traffic so it always generates such a reply.
390 These flows should not match IP fragments with nonzero offset.
394 Details TBD. Not yet implemented.
400 TCP reset. Priority-80 flows generate TCP reset messages in reply to
401 TCP datagrams directed to the router's IP address. The logical
402 router doesn't accept any TCP traffic so it always generates such a
407 These flows should not match IP fragments with nonzero offset.
411 Details TBD. Not yet implemented.
417 Protocol unreachable. Priority-70 flows generate ICMP protocol
418 unreachable messages in reply to packets directed to the router's IP
419 address on IP protocols other than UDP, TCP, and ICMP.
423 These flows should not match IP fragments with nonzero offset.
427 Details TBD. Not yet implemented.
432 Drop other IP traffic to this router. These flows drop any other
433 traffic destined to an IP address of this router that is not already
434 handled by one of the flows above, which amounts to ICMP (other than
435 echo requests) and fragments with nonzero offsets. For each IP address
436 <var>A</var> owned by the router, a priority-60 flow matches
437 <code>ip4.dst == <var>A</var></code> and drops the traffic.
442 The flows above handle all of the traffic that might be directed to the
443 router itself. The following flows (with lower priorities) handle the
444 remaining traffic, potentially for forwarding:
449 Drop Ethernet local broadcast. A priority-50 flow with match
450 <code>eth.bcast</code> drops traffic destined to the local Ethernet
451 broadcast address. By definition this traffic should not be forwarded.
455 Drop IP multicast. A priority-50 flow with match
456 <code>ip4.mcast</code> drops IP multicast traffic.
461 ICMP time exceeded. For each router port <var>P</var>, whose IP
462 address is <var>A</var>, a priority-40 flow with match <code>inport
463 == <var>P</var> && ip.ttl == {0, 1} &&
464 !ip.later_frag</code> matches packets whose TTL has expired, with the
465 following actions to send an ICMP time exceeded reply:
470 icmp4.type = 11; /* Time exceeded. */
471 icmp4.code = 0; /* TTL exceeded in transit. */
473 ip4.src = <var>A</var>;
485 TTL discard. A priority-30 flow with match <code>ip.ttl == {0,
486 1}</code> and actions <code>drop;</code> drops other packets whose TTL
487 has expired, that should not receive a ICMP error reply (i.e. fragments
488 with nonzero offset).
492 Next table. A priority-0 flows match all packets that aren't already
493 handled and uses actions <code>next;</code> to feed them to the ingress
498 <h3>Ingress Table 2: IP Routing</h3>
501 A packet that arrives at this table is an IP packet that should be routed
502 to the address in <code>ip4.dst</code>. This table implements IP
503 routing, setting <code>reg0</code> to the next-hop IP address (leaving
504 <code>ip4.dst</code>, the packet's final destination, unchanged) and
505 advances to the next table for ARP resolution.
509 This table contains the following logical flows:
515 Routing table. For each route to IPv4 network <var>N</var> with
516 netmask <var>M</var>, a logical flow with match <code>ip4.dst ==
517 <var>N</var>/<var>M</var></code>, whose priority is the number of
518 1-bits in <var>M</var>, has the following actions:
528 (Ingress table 1 already verified that <code>ip.ttl--;</code> will
529 not yield a TTL exceeded error.)
533 If the route has a gateway, <var>G</var> is the gateway IP address,
534 otherwise it is <code>ip4.dst</code>.
540 Destination unreachable. For each router port <var>P</var>, which
541 owns IP address <var>A</var>, a priority-0 logical flow with match
542 <code>in_port == <var>P</var> && !ip.later_frag &&
543 !icmp</code> has the following actions:
548 icmp4.type = 3; /* Destination unreachable. */
549 icmp4.code = 0; /* Network unreachable. */
551 ip4.src = <var>A</var>;
558 (The <code>!icmp</code> check prevents recursion if the destination
559 unreachable message itself cannot be routed.)
563 These flows are omitted if the logical router has a default route,
564 that is, a route with netmask 0.0.0.0.
569 <h3>Ingress Table 3: ARP Resolution</h3>
572 Any packet that reaches this table is an IP packet whose next-hop IP
573 address is in <code>reg0</code>. (<code>ip4.dst</code> is the final
574 destination.) This table resolves the IP address in <code>reg0</code>
575 into an output port in <code>outport</code> and an Ethernet address in
576 <code>eth.dst</code>, using the following flows:
582 Known MAC bindings. For each IP address <var>A</var> whose host is
583 known to have Ethernet address <var>HE</var> and reside on router
584 port <var>P</var> with Ethernet address <var>PE</var>, a priority-200
585 flow with match <code>reg0 == <var>A</var></code> has the following
590 eth.src = <var>PE</var>;
591 eth.dst = <var>HE</var>;
592 outport = <var>P</var>;
597 MAC bindings can be known statically based on data in the
598 <code>OVN_Northbound</code> database. For router ports connected to
599 logical switches, MAC bindings can be known statically from the
600 <code>addresses</code> column in the <code>Logical_Port</code> table.
601 For router ports connected to other logical routers, MAC bindings can
602 be known statically from the <code>mac</code> and
603 <code>network</code> column in the <code>Logical_Router_Port</code>
610 Unknown MAC bindings. For each non-gateway route to IPv4 network
611 <var>N</var> with netmask <var>M</var> on router port <var>P</var>
612 that owns IP address <var>A</var> and Ethernet address <var>E</var>,
613 a logical flow with match <code>ip4.dst ==
614 <var>N</var>/<var>M</var></code>, whose priority is the number of
615 1-bits in <var>M</var>, has the following actions:
620 eth.dst = ff:ff:ff:ff:ff:ff;
621 eth.src = <var>E</var>;
622 arp.sha = <var>E</var>;
623 arp.tha = 00:00:00:00:00:00;
624 arp.spa = <var>A</var>;
626 arp.op = 1; /* ARP request. */
627 outport = <var>P</var>;
633 TBD: How to install MAC bindings when an ARP response comes back.
634 (Implement a "learn" action?)
643 <h3>Egress Table 0: Delivery</h3>
646 Packets that reach this table are ready for delivery. It contains
647 priority-100 logical flows that match packets on each enabled logical
648 router port, with action <code>output;</code>.