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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 Priority-150 flows that matches ARP requests to each known IP address
208 <var>A</var> of logical port <var>P</var>, and respond ARP replies
209 directly with corresponding Ethernet address <var>E</var>:
212 eth.src = <var>E</var>;
213 arp.op = 2; /* ARP reply. */
215 arp.sha = <var>E</var>;
217 arp.spa = <var>A</var>;
218 outport = <var>P</var>;
219 inport = ""; /* Allow sending out inport. */
225 A priority-100 flow that outputs all packets with an Ethernet broadcast
226 or multicast <code>eth.dst</code> to the <code>MC_FLOOD</code>
227 multicast group, which <code>ovn-northd</code> populates with all
228 enabled logical ports.
232 One priority-50 flow that matches each known Ethernet address against
233 <code>eth.dst</code> and outputs the packet to the single associated
238 One priority-0 fallback flow that matches all packets and outputs them
239 to the <code>MC_UNKNOWN</code> multicast group, which
240 <code>ovn-northd</code> populates with all enabled logical ports that
241 accept unknown destination packets. As a small optimization, if no
242 logical ports accept unknown destination packets,
243 <code>ovn-northd</code> omits this multicast group and logical flow.
247 <h3>Egress Table 0: <code>to-lport</code> Pre-ACLs</h3>
250 This is similar to ingress table 1 except for <code>to-lport</code>
254 <h3>Egress Table 1: <code>to-lport</code> ACLs</h3>
257 This is similar to ingress table 2 except for <code>to-lport</code> ACLs.
260 <h3>Egress Table 2: Egress Port Security</h3>
263 This is similar to the ingress port security logic in ingress table 0,
264 but with important differences. Most obviously, <code>outport</code> and
265 <code>eth.dst</code> are checked instead of <code>inport</code> and
266 <code>eth.src</code>. Second, packets directed to broadcast or multicast
267 <code>eth.dst</code> are always accepted instead of being subject to the
268 port security rules; this is implemented through a priority-100 flow that
269 matches on <code>eth.mcast</code> with action <code>output;</code>.
270 Finally, to ensure that even broadcast and multicast packets are not
271 delivered to disabled logical ports, a priority-150 flow for each
272 disabled logical <code>outport</code> overrides the priority-100 flow
273 with a <code>drop;</code> action.
276 <h2>Logical Router Datapaths</h2>
278 <h3>Ingress Table 0: L2 Admission Control</h3>
281 This table drops packets that the router shouldn't see at all based on
282 their Ethernet headers. It contains the following flows:
287 Priority-100 flows to drop packets with VLAN tags or multicast Ethernet
292 For each enabled router port <var>P</var> with Ethernet address
293 <var>E</var>, a priority-50 flow that matches <code>inport ==
294 <var>P</var> && (eth.mcast || eth.dst ==
295 <var>E</var></code>), with action <code>next;</code>.
300 Other packets are implicitly dropped.
303 <h3>Ingress Table 1: IP Input</h3>
306 This table is the core of the logical router datapath functionality. It
307 contains the following flows to implement very basic IP host
314 L3 admission control: A priority-100 flow drops packets that match
315 any of the following:
320 <code>ip4.src[28..31] == 0xe</code> (multicast source)
323 <code>ip4.src == 255.255.255.255</code> (broadcast source)
326 <code>ip4.src == 127.0.0.0/8 || ip4.dst == 127.0.0.0/8</code>
327 (localhost source or destination)
330 <code>ip4.src == 0.0.0.0/8 || ip4.dst == 0.0.0.0/8</code> (zero
331 network source or destination)
334 <code>ip4.src</code> is any IP address owned by the router.
337 <code>ip4.src</code> is the broadcast address of any IP network
345 ICMP echo reply. These flows reply to ICMP echo requests received
346 for the router's IP address. Let <var>A</var> be an IP address or
347 broadcast address owned by a router port. Then, for each
348 <var>A</var>, a priority-90 flow matches on <code>ip4.dst ==
349 <var>A</var></code> and <code>icmp4.type == 8 && icmp4.code
350 == 0</code> (ICMP echo request). These flows use the following
351 actions where, if <var>A</var> is unicast, then <var>S</var> is
352 <var>A</var>, and if <var>A</var> is broadcast, <var>S</var> is the
353 router's IP address in <var>A</var>'s network:
358 ip4.src = <var>S</var>;
361 inport = ""; /* Allow sending out inport. */
366 Similar flows match on <code>ip4.dst == 255.255.255.255</code> and
367 each individual <code>inport</code>, and use the same actions in
368 which <var>S</var> is a function of <code>inport</code>.
374 ARP reply. These flows reply to ARP requests for the router's own IP
375 address. For each router port <var>P</var> that owns IP address
376 <var>A</var> and Ethernet address <var>E</var>, a priority-90 flow
377 matches <code>inport == <var>P</var> && arp.tpa ==
378 <var>A</var> && arp.op == 1</code> (ARP request) with the
384 eth.src = <var>E</var>;
385 arp.op = 2; /* ARP reply. */
387 arp.sha = <var>E</var>;
389 arp.spa = <var>A</var>;
390 outport = <var>P</var>;
391 inport = ""; /* Allow sending out inport. */
398 UDP port unreachable. Priority-80 flows generate ICMP port
399 unreachable messages in reply to UDP datagrams directed to the
400 router's IP address. The logical router doesn't accept any UDP
401 traffic so it always generates such a reply.
405 These flows should not match IP fragments with nonzero offset.
409 Details TBD. Not yet implemented.
415 TCP reset. Priority-80 flows generate TCP reset messages in reply to
416 TCP datagrams directed to the router's IP address. The logical
417 router doesn't accept any TCP traffic so it always generates such a
422 These flows should not match IP fragments with nonzero offset.
426 Details TBD. Not yet implemented.
432 Protocol unreachable. Priority-70 flows generate ICMP protocol
433 unreachable messages in reply to packets directed to the router's IP
434 address on IP protocols other than UDP, TCP, and ICMP.
438 These flows should not match IP fragments with nonzero offset.
442 Details TBD. Not yet implemented.
447 Drop other IP traffic to this router. These flows drop any other
448 traffic destined to an IP address of this router that is not already
449 handled by one of the flows above, which amounts to ICMP (other than
450 echo requests) and fragments with nonzero offsets. For each IP address
451 <var>A</var> owned by the router, a priority-60 flow matches
452 <code>ip4.dst == <var>A</var></code> and drops the traffic.
457 The flows above handle all of the traffic that might be directed to the
458 router itself. The following flows (with lower priorities) handle the
459 remaining traffic, potentially for forwarding:
464 Drop Ethernet local broadcast. A priority-50 flow with match
465 <code>eth.bcast</code> drops traffic destined to the local Ethernet
466 broadcast address. By definition this traffic should not be forwarded.
470 Drop IP multicast. A priority-50 flow with match
471 <code>ip4.mcast</code> drops IP multicast traffic.
476 ICMP time exceeded. For each router port <var>P</var>, whose IP
477 address is <var>A</var>, a priority-40 flow with match <code>inport
478 == <var>P</var> && ip.ttl == {0, 1} &&
479 !ip.later_frag</code> matches packets whose TTL has expired, with the
480 following actions to send an ICMP time exceeded reply:
485 icmp4.type = 11; /* Time exceeded. */
486 icmp4.code = 0; /* TTL exceeded in transit. */
488 ip4.src = <var>A</var>;
500 TTL discard. A priority-30 flow with match <code>ip.ttl == {0,
501 1}</code> and actions <code>drop;</code> drops other packets whose TTL
502 has expired, that should not receive a ICMP error reply (i.e. fragments
503 with nonzero offset).
507 Next table. A priority-0 flows match all packets that aren't already
508 handled and uses actions <code>next;</code> to feed them to the ingress
513 <h3>Ingress Table 2: IP Routing</h3>
516 A packet that arrives at this table is an IP packet that should be routed
517 to the address in <code>ip4.dst</code>. This table implements IP
518 routing, setting <code>reg0</code> to the next-hop IP address (leaving
519 <code>ip4.dst</code>, the packet's final destination, unchanged) and
520 advances to the next table for ARP resolution.
524 This table contains the following logical flows:
530 Routing table. For each route to IPv4 network <var>N</var> with
531 netmask <var>M</var>, a logical flow with match <code>ip4.dst ==
532 <var>N</var>/<var>M</var></code>, whose priority is the number of
533 1-bits in <var>M</var>, has the following actions:
543 (Ingress table 1 already verified that <code>ip.ttl--;</code> will
544 not yield a TTL exceeded error.)
548 If the route has a gateway, <var>G</var> is the gateway IP address,
549 otherwise it is <code>ip4.dst</code>.
555 Destination unreachable. For each router port <var>P</var>, which
556 owns IP address <var>A</var>, a priority-0 logical flow with match
557 <code>in_port == <var>P</var> && !ip.later_frag &&
558 !icmp</code> has the following actions:
563 icmp4.type = 3; /* Destination unreachable. */
564 icmp4.code = 0; /* Network unreachable. */
566 ip4.src = <var>A</var>;
573 (The <code>!icmp</code> check prevents recursion if the destination
574 unreachable message itself cannot be routed.)
578 These flows are omitted if the logical router has a default route,
579 that is, a route with netmask 0.0.0.0.
584 <h3>Ingress Table 3: ARP Resolution</h3>
587 Any packet that reaches this table is an IP packet whose next-hop IP
588 address is in <code>reg0</code>. (<code>ip4.dst</code> is the final
589 destination.) This table resolves the IP address in <code>reg0</code>
590 into an output port in <code>outport</code> and an Ethernet address in
591 <code>eth.dst</code>, using the following flows:
597 Known MAC bindings. For each IP address <var>A</var> whose host is
598 known to have Ethernet address <var>HE</var> and reside on router
599 port <var>P</var> with Ethernet address <var>PE</var>, a priority-200
600 flow with match <code>reg0 == <var>A</var></code> has the following
605 eth.src = <var>PE</var>;
606 eth.dst = <var>HE</var>;
607 outport = <var>P</var>;
612 MAC bindings can be known statically based on data in the
613 <code>OVN_Northbound</code> database. For router ports connected to
614 logical switches, MAC bindings can be known statically from the
615 <code>addresses</code> column in the <code>Logical_Port</code> table.
616 For router ports connected to other logical routers, MAC bindings can
617 be known statically from the <code>mac</code> and
618 <code>network</code> column in the <code>Logical_Router_Port</code>
625 Unknown MAC bindings. For each non-gateway route to IPv4 network
626 <var>N</var> with netmask <var>M</var> on router port <var>P</var>
627 that owns IP address <var>A</var> and Ethernet address <var>E</var>,
628 a logical flow with match <code>ip4.dst ==
629 <var>N</var>/<var>M</var></code>, whose priority is the number of
630 1-bits in <var>M</var>, has the following actions:
635 eth.dst = ff:ff:ff:ff:ff:ff;
636 eth.src = <var>E</var>;
637 arp.sha = <var>E</var>;
638 arp.tha = 00:00:00:00:00:00;
639 arp.spa = <var>A</var>;
641 arp.op = 1; /* ARP request. */
642 outport = <var>P</var>;
648 TBD: How to install MAC bindings when an ARP response comes back.
649 (Implement a "learn" action?)
658 <h3>Egress Table 0: Delivery</h3>
661 Packets that reach this table are ready for delivery. It contains
662 priority-100 logical flows that match packets on each enabled logical
663 router port, with action <code>output;</code>.