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30 .\" @(#)routed.8 8.2 (Berkeley) 12/11/93
38 .Nd network RIP and router discovery routing daemon
45 .Ar net Ns Op /mask Ns Op ,metric
51 utility is a daemon invoked at boot time to manage the network
53 It uses Routing Information Protocol, RIPv1 (RFC\ 1058),
55 and Internet Router Discovery Protocol (RFC 1256)
56 to maintain the kernel routing table.
57 The RIPv1 protocol is based on the reference
67 for Routing Information Protocol packets.
68 It also sends and receives multicast Router Discovery ICMP messages.
69 If the host is a router,
71 periodically supplies copies
72 of its routing tables to any directly connected hosts and networks.
73 It also advertises or solicits default routes using Router Discovery
76 When started (or when a network interface is later turned on),
78 uses an AF_ROUTE address family facility to find those
79 directly connected interfaces configured into the
80 system and marked "up".
81 It adds necessary routes for the interfaces
82 to the kernel routing table.
83 Soon after being first started, and provided there is at least one
84 interface on which RIP has not been disabled,
86 deletes all pre-existing
87 non-static routes in kernel table.
88 Static routes in the kernel table are preserved and
89 included in RIP responses if they have a valid RIP -hopcount
93 If more than one interface is present (not counting the loopback interface),
94 it is assumed that the host should forward packets among the
96 After transmitting a RIP
99 Router Discovery Advertisements or Solicitations on a new interface,
100 the daemon enters a loop, listening for
101 RIP request and response and Router Discovery packets from other hosts.
107 formulates a reply based on the information maintained in its
111 packet generated contains a list of known routes, each marked
112 with a "hop count" metric (a count of 16 or greater is
113 considered "infinite").
114 The advertised metric for a route reflects the metrics associated
118 though which it is received and sent,
119 so setting the metric on an interface
120 is an effective way to steer traffic.
127 Responses do not include routes with a first hop on the requesting
128 network to implement in part
130 Requests from query programs
133 are answered with the complete table.
135 The routing table maintained by the daemon
136 includes space for several gateways for each destination
137 to speed recovery from a failing router.
140 packets received are used to update the routing tables provided they are
141 from one of the several currently recognized gateways or
142 advertise a better metric than at least one of the existing
145 When an update is applied,
147 records the change in its own tables and updates the kernel routing table
148 if the best route to the destination changes.
149 The change in the kernel routing table is reflected in the next batch of
152 If the next response is not scheduled for a while, a
154 response containing only recently changed routes is sent.
156 In addition to processing incoming packets,
158 also periodically checks the routing table entries.
159 If an entry has not been updated for 3 minutes, the entry's metric
160 is set to infinity and marked for deletion.
161 Deletions are delayed until the route has been advertised with
162 an infinite metric to ensure the invalidation
163 is propagated throughout the local internet.
167 Routes in the kernel table that are added or changed as a result
168 of ICMP Redirect messages are deleted after a while to minimize
170 When a TCP connection suffers a timeout,
173 which deletes all redirected routes
174 through the gateway involved, advances the age of all RIP routes through
175 the gateway to allow an alternate to be chosen, and advances of the
176 age of any relevant Router Discovery Protocol default routes.
178 Hosts acting as internetwork routers gratuitously supply their
179 routing tables every 30 seconds to all directly connected hosts
181 These RIP responses are sent to the broadcast address on nets that support
183 to the destination address on point-to-point links, and to the router's
184 own address on other networks.
185 If RIPv2 is enabled, multicast packets are sent on interfaces that
186 support multicasting.
188 If no response is received on a remote interface, if there are errors
189 while sending responses,
190 or if there are more errors than input or output (see
192 then the cable or some other part of the interface is assumed to be
193 disconnected or broken, and routes are adjusted appropriately.
196 .Em Internet Router Discovery Protocol
197 is handled similarly.
198 When the daemon is supplying RIP routes, it also listens for
199 Router Discovery Solicitations and sends Advertisements.
200 When it is quiet and listening to other RIP routers, it
201 sends Solicitations and listens for Advertisements.
203 a good Advertisement and it is not multi-homed,
204 it stops listening for broadcast or multicast RIP responses.
205 It tracks several advertising routers to speed recovery when the
206 currently chosen router dies.
207 If all discovered routers disappear,
208 the daemon resumes listening to RIP responses.
209 It continues listening to RIP while using Router Discovery
210 if multi-homed to ensure all interfaces are used.
212 The Router Discovery standard requires that advertisements
213 have a default "lifetime" of 30 minutes.
215 something happen, a client can be without a good route for
217 It is a good idea to reduce the default to 45
219 .Fl P Cm rdisc_interval=45
220 on the command line or
221 .Cm rdisc_interval=45
226 While using Router Discovery (which happens by default when
227 the system has a single network interface and a Router Discover Advertisement
228 is received), there is a single default route and a variable number of
229 redirected host routes in the kernel table.
230 On a host with more than one network interface,
231 this default route will be via only one of the interfaces.
232 Thus, multi-homed hosts running with
240 facility described below to support "legacy" systems
241 that can handle neither RIPv2 nor Router Discovery.
243 By default, neither Router Discovery advertisements nor solicitations
244 are sent over point to point links (e.g.\& PPP).
245 The netmask associated with point-to-point links (such as SLIP
246 or PPP, with the IFF_POINTOPOINT flag) is used by
248 to infer the netmask used by the remote system when RIPv1 is used.
250 The following options are available:
251 .Bl -tag -width indent
255 to accept a RIP request from non-router node.
258 replies to a route information query from neighbor nodes.
259 When specified twice,
260 it replies to a query from remote nodes in addition.
262 utility can be used to send a request.
264 This feature is disabled by default because of a risk of reflection attack
265 though it is useful for debugging purpose.
269 to supply routing information.
270 This is the default if multiple network interfaces are present on which
271 RIP or Router Discovery have not been disabled, and if the kernel switch
274 is the opposite of the
277 This is the default when only one interface is present.
278 With this explicit option, the daemon is always in "quiet-mode" for RIP
279 and does not supply routing information to other computers.
281 do not run in the background.
282 This option is meant for interactive use.
284 used on internetwork routers to offer a route
285 to the "default" destination.
289 and is present mostly for historical reasons.
292 on the command line or
297 since a larger metric
298 will be used, reducing the spread of the potentially dangerous
300 This is typically used on a gateway to the Internet,
301 or on a gateway that uses another routing protocol whose routes
302 are not reported to other local routers.
303 Notice that because a metric of 1 is used, this feature is
305 It is more commonly accidentally used to create chaos with a
306 routing loop than to solve problems.
308 cause host or point-to-point routes to not be advertised,
309 provided there is a network route going the same direction.
310 That is a limited kind of aggregation.
311 This option is useful on gateways to Ethernets that have other gateway
312 machines connected with point-to-point links such as SLIP.
314 cause the machine to advertise a host or point-to-point route to
315 its primary interface.
316 It is useful on multi-homed machines such as NFS servers.
317 This option should not be used except when the cost of
318 the host routes it generates is justified by the popularity of
320 It is effective only when the machine is supplying
321 routing information, because there is more than one interface.
326 option to the limited extent of advertising the host route.
328 do not ignore RIPv2 authentication if we do not care about RIPv2
330 This option is required for conformance with RFC 1723.
331 However, it makes no sense and breaks using RIP as a discovery protocol
332 to ignore all RIPv2 packets that carry authentication when this machine
333 does not care about authentication.
335 increase the debugging level, which causes more information to be logged
336 on the tracefile specified with
339 The debugging level can be increased or decreased
347 .It Fl T Ar tracefile
348 increases the debugging level to at least 1 and
349 causes debugging information to be appended to the trace file.
350 Note that because of security concerns, it is wisest to not run
352 routinely with tracing directed to a file.
354 display and logs the version of daemon.
355 .It Fl F Ar net[/mask][,metric]
356 minimize routes in transmissions via interfaces with addresses that match
358 and synthesizes a default route to this machine with the
360 The intent is to reduce RIP traffic on slow, point-to-point links
361 such as PPP links by replacing many large UDP packets of RIP information
362 with a single, small packet containing a "fake" default route.
365 is absent, a value of 14 is assumed to limit
366 the spread of the "fake" default route.
367 This is a dangerous feature that when used carelessly can cause routing
369 Notice also that more than one interface can match the specified network
374 is equivalent to adding the parameter
382 Any other argument supplied is interpreted as the name
383 of a file in which the actions of
389 appending the name of the trace file to the command.
393 utility also supports the notion of
401 is started, it reads the file
403 to find such distant gateways which may not be located using
404 only information from a routing socket, to discover if some
405 of the local gateways are
407 and to obtain other parameters.
408 Gateways specified in this manner should be marked passive
409 if they are not expected to exchange routing information,
410 while gateways marked active
411 should be willing to exchange RIP packets.
414 gateways are installed in the
415 kernel's routing tables once upon startup and are not included in
416 transmitted RIP responses.
418 Distant active gateways are treated like network interfaces.
419 RIP responses are sent
423 If no responses are received, the associated route is deleted from
424 the kernel table and RIP responses advertised via other interfaces.
425 If the distant gateway resumes sending RIP responses, the associated
428 Such gateways can be useful on media that do not support broadcasts
429 or multicasts but otherwise act like classic shared media like
430 Ethernets such as some ATM networks.
431 One can list all RIP routers reachable on the HIPPI or ATM network in
435 Note that it is usually desirable to use RIPv2 in such situations
436 to avoid generating lists of inferred host routes.
440 are also passive, but are not placed in the kernel
441 routing table nor are they included in routing updates.
442 The function of external entries is to indicate
443 that another routing process
444 will install such a route if necessary,
445 and that other routes to that destination should not be installed
448 Such entries are only required when both routers may learn of routes
449 to the same destination.
453 file is comprised of a series of lines, each in
454 one of the following two formats or consist of parameters described later.
455 Blank lines and lines starting with '#' are comments.
463 .Pf < Cm passive No \&|
474 .Pf < Cm passive No \&|
482 is the name of the destination network or host.
483 It may be a symbolic network name or an Internet address
484 specified in "dot" notation (see
486 (If it is a name, then it must either be defined in
492 must be able to resolve it.)
495 is an optional number between 1 and 32 indicating the netmask associated
500 is the name or address of the gateway to which RIP responses should
504 is the hop count to the destination host or network.
508 .Cm net Ar nname/32 .
515 must be present to indicate whether the gateway should be treated as
519 (as described above),
520 or whether the gateway is
522 to the scope of the RIP protocol.
524 As can be seen when debugging is turned on with
526 such lines create pseudo-interfaces.
527 To set parameters for remote or external interfaces,
529 .Cm if=alias(Hname) ,
530 .Cm if=remote(Hname) ,
531 etc.\& should be used.
533 Lines that start with neither "net" nor "host" must consist of one
534 or more of the following parameter settings, separated by commas or
536 .Bl -tag -width indent
537 .It Cm if Ns = Ns Ar ifname
538 indicates that the other parameters on the line apply to the interface
541 .It Cm subnet Ns = Ns Ar nname Ns Oo / Ns Ar mask Oc Ns Op , Ns Ar metric
542 advertises a route to network
546 and the supplied metric (default 1).
547 This is useful for filling "holes" in CIDR allocations.
548 This parameter must appear by itself on a line.
549 The network number must specify a full, 32-bit value, as in 192.0.2.0
552 Do not use this feature unless necessary.
554 .It Cm ripv1_mask Ns = Ns Ar nname Ns / Ns Ar mask1 , Ns Ar mask2
555 specifies that netmask of the network of which
556 .Ar nname Ns / Ns Ar mask1
561 .Dq Li ripv1_mask=192.0.2.16/28,27
563 as a subnet of 192.0.2.0/27 instead of 192.0.2.0/24.
564 It is better to turn on RIPv2 instead of using this facility, for example
567 .It Cm passwd Ns = Ns Ar XXX[|KeyID[start|stop]]
568 specifies a RIPv2 cleartext password that will be included on
569 all RIPv2 responses sent, and checked on all RIPv2 responses received.
570 Any blanks, tab characters, commas, or '#', '|', or NULL characters in the
571 password must be escaped with a backslash (\\).
572 The common escape sequences \\n, \\r, \\t, \\b, and \\xxx have their
576 must be unique but is ignored for cleartext passwords.
581 are timestamps in the form year/month/day@hour:minute.
582 They specify when the password is valid.
583 The valid password with the most future is used on output packets, unless
584 all passwords have expired, in which case the password that expired most
585 recently is used, or unless no passwords are valid yet, in which case
586 no password is output.
587 Incoming packets can carry any password that is valid, will
588 be valid within the next 24 hours, or that was valid within the preceding
590 To protect the secrets, the passwd settings are valid only in the
592 file and only when that file is readable only by UID 0.
593 .It Cm md5_passwd Ns \&= Ns Ar XXX|KeyID[start|stop]
594 specifies a RIPv2 MD5 password.
597 is required, this keyword is similar to
600 turns off aggregation of subnets in RIPv1 and RIPv2 responses.
602 turns off aggregation of networks into supernets in RIPv2 responses.
604 marks the interface to not be advertised in updates sent via other
605 interfaces, and turns off all RIP and router discovery through the interface.
607 disables all RIP processing on the specified interface.
608 If no interfaces are allowed to process RIP packets,
610 acts purely as a router discovery daemon.
612 Note that turning off RIP without explicitly turning on router
613 discovery advertisements with
619 to act as a client router discovery daemon, not advertising.
621 causes RIPv2 packets to be broadcast instead of multicast.
623 causes no RIP updates to be sent.
625 causes RIPv1 received responses to be ignored.
627 causes RIPv2 received responses to be ignored.
629 turns on RIPv2 output and causes RIPv2 advertisements to be
630 multicast when possible.
638 disables the Internet Router Discovery Protocol.
640 disables the transmission of Router Discovery Solicitations.
642 specifies that Router Discovery solicitations should be sent,
643 even on point-to-point links,
644 which by default only listen to Router Discovery messages.
646 disables the transmission of Router Discovery Advertisements.
648 specifies that Router Discovery Advertisements should be sent,
649 even on point-to-point links,
650 which by default only listen to Router Discovery messages.
652 specifies that Router Discovery packets should be broadcast instead of
654 .It Cm rdisc_pref Ns \&= Ns Ar N
655 sets the preference in Router Discovery Advertisements to the optionally
658 The default preference is 0.
659 Default routes with smaller or more negative preferences are preferred by
661 .It Cm rdisc_interval Ns \&= Ns Ar N
662 sets the nominal interval with which Router Discovery Advertisements
663 are transmitted to N seconds and their lifetime to 3*N.
664 .It Cm fake_default Ns \&= Ns Ar metric
665 has an identical effect to
666 .Fl F Ar net[/mask][=metric]
667 with the network and mask coming from the specified interface.
671 When RIPv2 routes are multicast, so that RIPv1 listeners cannot
672 receive them, this feature causes a RIPv1 default route to be
673 broadcast to RIPv1 listeners.
676 the default route is broadcast with a metric of 14.
677 That serves as a "poor man's router discovery" protocol.
678 .It Cm adj_inmetric Ns \&= Ns Ar delta
679 adjusts the hop count or metric of received RIP routes by
681 The metric of every received RIP route is increased by the sum
682 of two values associated with the interface.
683 One is the adj_inmetric value and the other is the interface
686 .It Cm adj_outmetric Ns \&= Ns Ar delta
687 adjusts the hop count or metric of advertised RIP routes by
689 The metric of every received RIP route is increased by the metric
690 associated with the interface by which it was received, or by 1 if
691 the interface does not have a non-zero metric.
692 The metric of the received route is then increased by the
693 adj_outmetric associated with the interface.
694 Every advertised route is increased by a total of four
696 the metric set for the interface by which it was received with
699 .Cm adj_inmetric Ar delta
700 of the receiving interface,
701 the metric set for the interface by which it is transmitted with
704 .Cm adj_outmetric Ar delta
705 of the transmitting interface.
706 .It Cm trust_gateway Ns \&= Ns Ar rname[|net1/mask1|net2/mask2|...]
707 causes RIP packets from router
709 and other routers named in other
711 keywords to be accepted, and packets from other routers to be ignored.
712 If networks are specified, then routes to other networks will be ignored
715 allows the kernel to listen ICMP Redirect messages when the system is acting
716 as a router and forwarding packets.
717 Otherwise, ICMP Redirect messages are overridden and deleted when the
718 system is acting as a router.
721 .Bl -tag -width /etc/gateways -compact
730 .%T Internet Transport Protocols
732 .%Q Xerox System Integration Standard
739 .\" LocalWords: loopback ICMP rtquery ifconfig multicasting Solicitations RIPv
740 .\" LocalWords: netstat rdisc
742 It does not always detect unidirectional failures in network interfaces,
743 for example, when the output side fails.