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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>;
343 inport = \"\"; /* Allow sending out inport. */
348 Similar flows match on <code>ip4.dst == 255.255.255.255</code> and
349 each individual <code>inport</code>, and use the same actions in
350 which <var>S</var> is a function of <code>inport</code>.
356 ARP reply. These flows reply to ARP requests for the router's own IP
357 address. For each router port <var>P</var> that owns IP address
358 <var>A</var> and Ethernet address <var>E</var>, a priority-90 flow
359 matches <code>inport == <var>P</var> && arp.tpa ==
360 <var>A</var> && arp.op == 1</code> (ARP request) with the
366 eth.src = <var>E</var>;
367 arp.op = 2; /* ARP reply. */
369 arp.sha = <var>E</var>;
371 arp.spa = <var>A</var>;
372 outport = <var>P</var>;
373 inport = \"\"; /* Allow sending out inport. */
380 UDP port unreachable. Priority-80 flows generate ICMP port
381 unreachable messages in reply to UDP datagrams directed to the
382 router's IP address. The logical router doesn't accept any UDP
383 traffic so it always generates such a reply.
387 These flows should not match IP fragments with nonzero offset.
391 Details TBD. Not yet implemented.
397 TCP reset. Priority-80 flows generate TCP reset messages in reply to
398 TCP datagrams directed to the router's IP address. The logical
399 router doesn't accept any TCP traffic so it always generates such a
404 These flows should not match IP fragments with nonzero offset.
408 Details TBD. Not yet implemented.
414 Protocol unreachable. Priority-70 flows generate ICMP protocol
415 unreachable messages in reply to packets directed to the router's IP
416 address on IP protocols other than UDP, TCP, and ICMP.
420 These flows should not match IP fragments with nonzero offset.
424 Details TBD. Not yet implemented.
429 Drop other IP traffic to this router. These flows drop any other
430 traffic destined to an IP address of this router that is not already
431 handled by one of the flows above, which amounts to ICMP (other than
432 echo requests) and fragments with nonzero offsets. For each IP address
433 <var>A</var> owned by the router, a priority-60 flow matches
434 <code>ip4.dst == <var>A</var></code> and drops the traffic.
439 The flows above handle all of the traffic that might be directed to the
440 router itself. The following flows (with lower priorities) handle the
441 remaining traffic, potentially for forwarding:
446 Drop Ethernet local broadcast. A priority-50 flow with match
447 <code>eth.bcast</code> drops traffic destined to the local Ethernet
448 broadcast address. By definition this traffic should not be forwarded.
452 Drop IP multicast. A priority-50 flow with match
453 <code>ip4.mcast</code> drops IP multicast traffic.
458 ICMP time exceeded. For each router port <var>P</var>, whose IP
459 address is <var>A</var>, a priority-40 flow with match <code>inport
460 == <var>P</var> && ip.ttl == {0, 1} &&
461 !ip.later_frag</code> matches packets whose TTL has expired, with the
462 following actions to send an ICMP time exceeded reply:
467 icmp4.type = 11; /* Time exceeded. */
468 icmp4.code = 0; /* TTL exceeded in transit. */
470 ip4.src = <var>A</var>;
482 TTL discard. A priority-30 flow with match <code>ip.ttl == {0,
483 1}</code> and actions <code>drop;</code> drops other packets whose TTL
484 has expired, that should not receive a ICMP error reply (i.e. fragments
485 with nonzero offset).
489 Next table. A priority-0 flows match all packets that aren't already
490 handled and uses actions <code>next;</code> to feed them to the ingress
495 <h3>Ingress Table 2: IP Routing</h3>
498 A packet that arrives at this table is an IP packet that should be routed
499 to the address in <code>ip4.dst</code>. This table implements IP
500 routing, setting <code>reg0</code> to the next-hop IP address (leaving
501 <code>ip4.dst</code>, the packet's final destination, unchanged) and
502 advances to the next table for ARP resolution.
506 This table contains the following logical flows:
512 Routing table. For each route to IPv4 network <var>N</var> with
513 netmask <var>M</var>, a logical flow with match <code>ip4.dst ==
514 <var>N</var>/<var>M</var></code>, whose priority is the number of
515 1-bits in <var>M</var>, has the following actions:
525 (Ingress table 1 already verified that <code>ip.ttl--;</code> will
526 not yield a TTL exceeded error.)
530 If the route has a gateway, <var>G</var> is the gateway IP address,
531 otherwise it is <code>ip4.dst</code>.
537 Destination unreachable. For each router port <var>P</var>, which
538 owns IP address <var>A</var>, a priority-0 logical flow with match
539 <code>in_port == <var>P</var> && !ip.later_frag &&
540 !icmp</code> has the following actions:
545 icmp4.type = 3; /* Destination unreachable. */
546 icmp4.code = 0; /* Network unreachable. */
548 ip4.src = <var>A</var>;
555 (The <code>!icmp</code> check prevents recursion if the destination
556 unreachable message itself cannot be routed.)
560 These flows are omitted if the logical router has a default route,
561 that is, a route with netmask 0.0.0.0.
566 <h3>Ingress Table 3: ARP Resolution</h3>
569 Any packet that reaches this table is an IP packet whose next-hop IP
570 address is in <code>reg0</code>. (<code>ip4.dst</code> is the final
571 destination.) This table resolves the IP address in <code>reg0</code>
572 into an output port in <code>outport</code> and an Ethernet address in
573 <code>eth.dst</code>, using the following flows:
579 Known MAC bindings. For each IP address <var>A</var> whose host is
580 known to have Ethernet address <var>HE</var> and reside on router
581 port <var>P</var> with Ethernet address <var>PE</var>, a priority-200
582 flow with match <code>reg0 == <var>A</var></code> has the following
587 eth.src = <var>PE</var>;
588 eth.dst = <var>HE</var>;
589 outport = <var>P</var>;
594 MAC bindings can be known statically based on data in the
595 <code>OVN_Northbound</code> database. For router ports connected to
596 logical switches, MAC bindings can be known statically from the
597 <code>addresses</code> column in the <code>Logical_Port</code> table.
598 For router ports connected to other logical routers, MAC bindings can
599 be known statically from the <code>mac</code> and
600 <code>network</code> column in the <code>Logical_Router_Port</code>
607 Unknown MAC bindings. For each non-gateway route to IPv4 network
608 <var>N</var> with netmask <var>M</var> on router port <var>P</var>
609 that owns IP address <var>A</var> and Ethernet address <var>E</var>,
610 a logical flow with match <code>ip4.dst ==
611 <var>N</var>/<var>M</var></code>, whose priority is the number of
612 1-bits in <var>M</var>, has the following actions:
617 eth.dst = ff:ff:ff:ff:ff:ff;
618 eth.src = <var>E</var>;
619 arp.sha = <var>E</var>;
620 arp.tha = 00:00:00:00:00:00;
621 arp.spa = <var>A</var>;
623 arp.op = 1; /* ARP request. */
624 outport = <var>P</var>;
630 TBD: How to install MAC bindings when an ARP response comes back.
631 (Implement a "learn" action?)
640 <h3>Egress Table 0: Delivery</h3>
643 Packets that reach this table are ready for delivery. It contains
644 priority-100 logical flows that match packets on each enabled logical
645 router port, with action <code>output;</code>.