452 lines
15 KiB
Groff
452 lines
15 KiB
Groff
.\" $NetBSD: mrouted.8,v 1.17 2009/03/15 10:16:28 joerg Exp $
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.\" $OpenBSD: mrouted.8,v 1.11 2003/03/03 15:14:28 deraadt Exp $
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.\" The mrouted program is covered by the license in the accompanying file
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.\" named "LICENSE". Use of the mrouted program represents acceptance of
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.\" the terms and conditions listed in that file.
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.\"
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.\" The mrouted program is COPYRIGHT 1989 by The Board of Trustees of
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.\" Leland Stanford Junior University.
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.Dd May 8, 1995
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.Dt MROUTED 8
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.Os
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.Sh NAME
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.Nm mrouted
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.Nd IP multicast routing daemon
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.Sh SYNOPSIS
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.Nm mrouted
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.Op Fl c Ar config_file
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.Op Fl d Ar debug_level
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.Op Fl p
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.Sh DESCRIPTION
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.Nm
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is an implementation of the Distance-Vector Multicast Routing
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Protocol (DVMRP), an earlier version of which is specified in RFC 1075.
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It maintains topological knowledge via a distance-vector routing protocol
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(like RIP, described in RFC 1058), upon which it implements a multicast
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datagram forwarding algorithm called Reverse Path Multicasting.
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.Pp
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.Nm
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forwards a multicast datagram along a shortest (reverse) path tree
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rooted at the subnet on which the datagram originates.
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The multicast
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delivery tree may be thought of as a broadcast delivery tree that has
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been pruned back so that it does not extend beyond those subnetworks
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that have members of the destination group.
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Hence, datagrams are not forwarded along those branches which have no
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listeners of the multicast group.
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The IP time-to-live of a multicast datagram can be
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used to limit the range of multicast datagrams.
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.Pp
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In order to support multicasting among subnets that are separated by (unicast)
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routers that do not support IP multicasting,
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.Nm
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includes support for
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"tunnels", which are virtual point-to-point links between pairs of
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.Nm
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daemons located anywhere in an internet.
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IP multicast packets are encapsulated
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for transmission through tunnels, so that they look like normal unicast
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datagrams to intervening routers and subnets.
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The encapsulation is added on
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entry to a tunnel, and stripped off on exit from a tunnel.
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By default, the packets are encapsulated using the IP-in-IP protocol
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(IP protocol number 4).
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Older versions of
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.Nm
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tunnel using IP source routing, which puts a heavy load on some
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types of routers.
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This version does not support IP source route tunneling.
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.Pp
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The tunneling mechanism allows
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.Nm
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to establish a virtual internet, for
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the purpose of multicasting only, which is independent of the physical
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internet, and which may span multiple Autonomous Systems.
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This capability
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is intended for experimental support of internet multicasting only, pending
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widespread support for multicast routing by the regular (unicast) routers.
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.Nm
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suffers from the well-known scaling problems of any distance-vector
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routing protocol, and does not (yet) support hierarchical multicast routing.
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.Pp
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.Nm
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handles multicast routing only; there may or may not be unicast routing
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software running on the same machine as
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.Nm mrouted .
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With the use of tunnels, it is not necessary for
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.Nm
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to have access to more than one physical subnet
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in order to perform multicast forwarding.
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.Sh INVOCATION
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If no
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.Fl d
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option is given, or if the debug level is specified as 0,
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.Nm
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detaches from the invoking terminal.
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Otherwise, it remains attached to the
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invoking terminal and responsive to signals from that terminal.
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If
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.Fl d
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is given with no argument, the debug level defaults to 2.
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Regardless of the debug level,
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.Nm
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always writes warning and error messages to the system
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log daemon.
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Non-zero debug levels have the following effects:
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.Bl -hang -compact -offset indent
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.It 1
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all syslog'ed messages are also printed to stderr.
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.It 2
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all level 1 messages plus notifications of "significant"
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events are printed to stderr.
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.It 3
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all level 2 messages plus notifications of all packet
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arrivals and departures are printed to stderr.
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.El
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.Pp
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Upon startup, mrouted writes its pid to the file
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.Pa /var/run/mrouted.pid .
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.Sh CONFIGURATION
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.Nm
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automatically configures itself to forward on all multicast-capable
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interfaces, i.e., interfaces that have the IFF_MULTICAST flag set (excluding
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the loopback "interface"), and it finds other
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.Nm
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directly reachable via those interfaces.
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To override the default configuration, or to add tunnel links to other
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.Nm
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configuration commands may be placed in
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.Pa /etc/mrouted.conf
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(or an alternative file, specified by the
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.Fl c
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option).
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There are four types of configuration commands:
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.Bl -item -offset indent
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.It
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.Tn phyint \*[Lt]local-addr\*[Gt] [disable] [metric \*[Lt]m\*[Gt]]
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.Bl -tag -width flag -compact -offset indent
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.It [threshold \*[Lt]t\*[Gt]] [rate_limit \*[Lt]b\*[Gt]]
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.It [boundary (\*[Lt]boundary-name\*[Gt]|\*[Lt]scoped-addr\*[Gt]/\*[Lt]mask-len\*[Gt])]
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.It [altnet \*[Lt]network\*[Gt]/\*[Lt]mask-len\*[Gt]]
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.El
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.It
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.Bl -tag -width flag -compact -offset indent
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.It Tn tunnel \*[Lt]local-addr\*[Gt] \*[Lt]remote-addr\*[Gt] [metric \*[Lt]m\*[Gt]]
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.It [threshold \*[Lt]t\*[Gt]] [rate_limit \*[Lt]b\*[Gt]]
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.It [boundary (\*[Lt]boundary-name\*[Gt]|\*[Lt]scoped-addr\*[Gt]/\*[Lt]mask-len\*[Gt])]
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.El
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.It
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.Tn cache_lifetime \*[Lt]ct\*[Gt]
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.It
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.Tn pruning \*[Lt]off/on\*[Gt]
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.It
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.Tn name \*[Lt]boundary-name\*[Gt] \*[Lt]scoped-addr\*[Gt]/\*[Lt]mask-len\*[Gt]
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.El
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.Pp
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The file format is free-form; whitespace (including newlines) is not
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significant.
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The
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.Ar boundary
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and
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.Ar altnet
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options may be specified as many times as necessary.
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.Pp
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The phyint command can be used to disable multicast routing on the physical
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interface identified by local IP address
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.Ar \*[Lt]local-addr\*[Gt] ,
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or to associate a non-default metric or threshold with the specified
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physical interface.
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The local IP address
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.Ar \*[Lt]local-addr\*[Gt]
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may be replaced by the interface name (e.g., le0).
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If a phyint is attached to multiple IP subnets, describe each additional subnet
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with the altnet keyword.
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Phyint commands must precede tunnel commands.
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.Pp
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The tunnel command can be used to establish a tunnel link between local
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IP address
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.Ar \*[Lt]local-addr\*[Gt]
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and remote IP address
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.Ar \*[Lt]remote-addr\*[Gt] ,
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and to associate a non-default metric or threshold with that tunnel.
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The local IP address
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.Ar \*[Lt]local-addr\*[Gt]
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may be replaced by the interface name (e.g., le0).
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The remote IP address
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.Ar \*[Lt]remote-addr\*[Gt]
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may be replaced by a host name, if and only if the host name has a single
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IP address associated with it.
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The tunnel must be set up in the mrouted.conf files of both routers before
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it can be used.
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.\"For backwards compatibility with older
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.\".IR mrouted s,
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.\"the srcrt keyword specifies
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.\"encapsulation using IP source routing.
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.Pp
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The cache_lifetime is a value that determines the amount of time that a
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cached multicast route stays in kernel before timing out.
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The value of this entry should lie between 300 (5 min) and 86400 (1 day).
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It defaults to 300.
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.Pp
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The
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.Ar pruning
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option is provided for
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.Nm
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to act as a non-pruning router.
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It is also possible to start
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.Nm
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in a non-pruning mode using the
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.Fl p
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option on the command line.
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It is expected that a router would be configured
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in this manner for test purposes only.
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The default mode is pruning enabled.
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.Pp
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You may assign names to boundaries to make configuration easier with
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the name keyword.
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The boundary option on phyint or tunnel commands
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can accept either a name or a boundary.
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.Pp
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The metric is the "cost" associated with sending a datagram on the given
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interface or tunnel; it may be used to influence the choice of routes.
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The metric defaults to 1.
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Metrics should be kept as small as possible, because
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.Nm
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cannot route along paths with a sum of metrics greater than 31.
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.Pp
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The threshold is the minimum IP time-to-live required for a multicast datagram
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to be forwarded to the given interface or tunnel.
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It is used to control the scope of multicast datagrams.
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(The TTL of forwarded packets is only compared
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to the threshold, it is not decremented by the threshold.
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Every multicast router decrements the TTL by 1.)
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The default threshold is 1.
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.Pp
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In general, all
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.Nm
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connected to a particular subnet or tunnel should
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use the same metric and threshold for that subnet or tunnel.
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.Pp
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The rate_limit option allows the network administrator to specify a
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certain bandwidth in Kbits/second which would be allocated to multicast
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traffic.
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It defaults to 500Kbps on tunnels, and 0 (unlimited) on physical
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interfaces.
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.Pp
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The boundary option allows an interface
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to be configured as an administrative boundary for the specified
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scoped address.
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Packets belonging to this address will not
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be forwarded on a scoped interface.
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The boundary option accepts either
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a name or a boundary spec.
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.Pp
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.Nm
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will not initiate execution if it has fewer than two enabled vifs,
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where a vif (virtual interface) is either a physical multicast-capable
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interface or a tunnel.
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It will log a warning if all of its vifs are tunnels; such an
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.Nm
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configuration would be better replaced by more
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direct tunnels (i.e., eliminate the middle man).
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.Sh EXAMPLE CONFIGURATION
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This is an example configuration for a mythical multicast router at a big
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school.
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.Bd -unfilled -compact -offset left
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#
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# mrouted.conf example
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#
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# Name our boundaries to make it easier.
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name LOCAL 239.255.0.0/16
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name EE 239.254.0.0/16
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#
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# le1 is our gateway to compsci, don't forward our
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# local groups to them.
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phyint le1 boundary EE
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#
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# le2 is our interface on the classroom net, it has four
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# different length subnets on it.
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# Note that you can use either an ip address or an
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# interface name
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phyint 172.16.12.38 boundary EE altnet 172.16.15.0/26
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altnet 172.16.15.128/26 altnet 172.16.48.0/24
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#
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# atm0 is our ATM interface, which doesn't properly
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# support multicasting.
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phyint atm0 disable
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#
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# This is an internal tunnel to another EE subnet.
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# Remove the default tunnel rate limit, since this
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# tunnel is over ethernets.
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tunnel 192.168.5.4 192.168.55.101 metric 1 threshold 1
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rate_limit 0
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#
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# This is our tunnel to the outside world.
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# Careful with those boundaries, Eugene.
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tunnel 192.168.5.4 10.11.12.13 metric 1 threshold 32
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boundary LOCAL boundary EE
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.Ed
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.Sh SIGNALS
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.Nm
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responds to the following signals:
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.Bl -tag -width TERM -compact
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.It HUP
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restarts
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.Nm mrouted .
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The configuration file is reread every time this signal is evoked.
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.It INT
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terminates execution gracefully (i.e., by sending
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good-bye messages to all neighboring routers).
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.It TERM
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same as INT
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.It USR1
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dumps the internal routing tables to
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.Pa /var/tmp/mrouted.dump .
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.It USR2
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dumps the internal cache tables to
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.Pa /var/tmp/mrouted.cache .
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.It QUIT
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dumps the internal routing tables to stderr (only if
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.Nm
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was invoked with a non-zero debug level).
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.El
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.Pp
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For convenience in sending signals,
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.Nm
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writes its pid to
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.Pa /var/run/mrouted.pid
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upon startup.
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.Sh FILES
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.Bl -tag -width /var/tmp/mrouted.cache -compact
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.It Pa /etc/mrouted.conf
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.It Pa /var/run/mrouted.pid
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.It Pa /var/tmp/mrouted.dump
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.It Pa /var/tmp/mrouted.cache
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.El
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.Sh EXAMPLES
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The routing tables look like this:
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.Pp
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.Bd -literal -compact -offset left
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Virtual Interface Table
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Vif Local-Address Metric Thresh Flags
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0 36.2.0.8 subnet: 36.2 1 1 querier
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groups: 224.0.2.1
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224.0.0.4
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pkts in: 3456
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pkts out: 2322323
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1 36.11.0.1 subnet: 36.11 1 1 querier
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groups: 224.0.2.1
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224.0.1.0
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224.0.0.4
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pkts in: 345
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pkts out: 3456
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2 36.2.0.8 tunnel: 36.8.0.77 3 1
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peers: 36.8.0.77 (2.2)
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boundaries: 239.0.1
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: 239.1.2
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pkts in: 34545433
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pkts out: 234342
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3 36.2.0.8 tunnel: 36.6.8.23 3 16
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Multicast Routing Table (1136 entries)
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Origin-Subnet From-Gateway Metric Tmr In-Vif Out-Vifs
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36.2 1 45 0 1* 2 3*
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36.8 36.8.0.77 4 15 2 0* 1* 3*
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36.11 1 20 1 0* 2 3*
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.
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.
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.
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.Ed
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.Pp
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In this example, there are four vifs connecting to two subnets and two
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tunnels.
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The vif 3 tunnel is not in use (no peer address).
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The vif 0 and
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vif 1 subnets have some groups present; tunnels never have any groups.
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This instance of
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.Nm
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is the one responsible for sending periodic group
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membership queries on the vif 0 and vif 1 subnets, as indicated by the
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"querier" flags.
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The list of boundaries indicate the scoped addresses on that interface.
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A count of the number of incoming and outgoing packets is also
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shown at each interface.
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.Pp
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Associated with each subnet from which a multicast datagram can originate
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is the address of the previous hop router (unless the subnet is directly-
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connected), the metric of the path back to the origin, the amount of time
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since we last received an update for this subnet, the incoming vif for
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multicasts from that origin, and a list of outgoing vifs.
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"*" means that
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the outgoing vif is connected to a leaf of the broadcast tree rooted at the
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origin, and a multicast datagram from that origin will be forwarded on that
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outgoing vif only if there are members of the destination group on that leaf.
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.Pp
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.Nm
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also maintains a copy of the kernel forwarding cache table.
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Entries are created and deleted by
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.Nm mrouted .
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.Pp
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The cache tables look like this:
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.Pp
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.Bd -unfilled -compact -offset left
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Multicast Routing Cache Table (147 entries)
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Origin Mcast-group CTmr Age Ptmr IVif Forwvifs
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13.2.116/22 224.2.127.255 3m 2m - 0 1
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\*[Gt]13.2.116.19
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\*[Gt]13.2.116.196
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138.96.48/21 224.2.127.255 5m 2m - 0 1
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\*[Gt]138.96.48.108
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128.9.160/20 224.2.127.255 3m 2m - 0 1
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\*[Gt]128.9.160.45
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198.106.194/24 224.2.135.190 9m 28s 9m 0P
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\*[Gt]198.106.194.22
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.Ed
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.Pp
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Each entry is characterized by the origin subnet number and mask and the
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destination multicast group.
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The 'CTmr' field indicates the lifetime of the entry.
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The entry is deleted from the cache table
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when the timer decrements to zero.
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The 'Age' field is the time since
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this cache entry was originally created.
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Since cache entries get refreshed
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if traffic is flowing, routing entries can grow very old.
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The 'Ptmr' field is simply a dash if no prune was sent upstream, or the
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amount of time until the upstream prune will time out.
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The 'Ivif' field indicates the
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incoming vif for multicast packets from that origin.
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Each router also
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maintains a record of the number of prunes received from neighboring
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routers for a particular source and group.
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If there are no members of
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a multicast group on any downward link of the multicast tree for a
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subnet, a prune message is sent to the upstream router.
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They are indicated by a "P" after the vif number.
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The Forwvifs field shows the
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interfaces along which datagrams belonging to the source-group are
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forwarded.
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A "p" indicates that no datagrams are being forwarded along
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that interface.
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An unlisted interface is a leaf subnet with are no
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members of the particular group on that subnet.
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A "b" on an interface
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indicates that it is a boundary interface, i.e., traffic will not be
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forwarded on the scoped address on that interface.
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An additional line with a "\*[Gt]" as the first character is printed for
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each source on the subnet.
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Note that there can be many sources in one subnet.
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.Sh SEE ALSO
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.Xr map-mbone 8 ,
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.Xr mrinfo 8 ,
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.Xr mtrace 8
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.Pp
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DVMRP is described, along with other multicast routing algorithms, in the
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paper "Multicast Routing in Internetworks and Extended LANs" by S. Deering,
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in the Proceedings of the ACM SIGCOMM '88 Conference.
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.Sh AUTHORS
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Steve Deering, Ajit Thyagarajan, Bill Fenner
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