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584 lines
21 KiB
Groff
584 lines
21 KiB
Groff
.\"COPYRIGHT 1989 by The Board of Trustees of Leland Stanford Junior University.
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.\"$Id: mrouted.8,v 1.12 1999/01/20 07:55:51 fenner Exp $
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.Dd May 8, 1995
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.Dt MROUTED 8
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.UC 5
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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 Op Ar debug_level
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.Op Fl p
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.Sh DESCRIPTION
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.Nm Mrouted
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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 Mrouted
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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. 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. Hence, datagrams
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are not forwarded along those branches which have no listeners of the
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multicast group. 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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multicast routers
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located anywhere in an internet. IP multicast packets are encapsulated for
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transmission through tunnels, so that they look like normal unicast datagrams
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to intervening routers and subnets. The encapsulation
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is added on entry to a tunnel, and stripped off
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on exit from a tunnel.
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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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tunneled 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 tunnelling.
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.Pp
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The tunnelling 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. 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 Mrouted
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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 Mrouted
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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
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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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.Pp
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The following options are available:
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.Bl -tag -width indent
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.It Fl c Ar config_file
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Specify an alternative file for configuration commands. Default is
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.Pa /etc/mrouted.conf .
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.It Fl d Op Ar debug_level
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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. Otherwise, it remains attached to the
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invoking terminal and responsive to signals from that terminal.
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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 demon. The
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.Fl debug-level
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argument is a comma-seperated list of any of the following:
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.Bl -tag -width indent
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.It "packet"
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Display the type, source and destination of all packets sent or received.
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.It "pruning"
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Display more information about prunes sent or received.
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.It "routing"
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Display more information about routing update packets sent or received.
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.It "route_detail"
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Display routing updates in excruciating detail. This is generally way too
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much information.
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.It "neighbors"
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Display information about neighbor discovery.
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.It "cache"
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Display insertions, deletions and refreshes of entries in
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the kernel forwarding cache.
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.It "timeout"
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Debug timeouts and periodic processes.
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.It "interface"
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Display information about interfaces and their configuration.
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.It "membership"
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Display information about group memberships on physical interfaces.
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.It "traceroute"
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Display information about multicast traceroute requests
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passing through this router.
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.It "igmp"
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Display IGMP operation including group membership and querier election.
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.It "icmp"
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Monitor ICMP handling.
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.It "rsrr"
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Monitor RSRR operation.
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.El
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.Pp
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Upon startup,
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.Nm
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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 Mrouted
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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 DVMRP routers directly reachable
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via those interfaces. To override the default configuration, or to add
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tunnel links to other multicast routers,
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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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.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 file begins with commands that apply to
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.Nm mrouted Ns 's
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overall operation or set defaults.
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.Bl -tag -width indent
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.It cache_lifetime Ar secs
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Specifies, in seconds, the lifetime of a multicast forwarding cache
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entry in the kernel. Multicast forwarding cache entries in the kernel
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are checked every
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.Ar secs
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seconds, and are refreshed if the source is still
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active or deleted if not. Care should be taken when setting this value,
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as a low value can keep the kernel cache small at the cost of "thrashing"
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the cache for periodic senders, but high values can cause the kernel
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cache to grow unacceptably large. The default is 300 seconds (5 minutes).
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.It prune_lifetime Ar secs
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Sepcifies, in seconds, the average lifetime of prunes that are sent towards
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parents. The actual lifetimes will be randomized in the range
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[.5\fIsecs\fP,1.5\fIsecs\fP]. The default is 7200 (2 hours). Smaller values
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cause less state to be kept both at this router and the parent, at the
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cost of more frequent broadcasts. However, some routers (e.g. mrouted <3.3
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and all currently known versions of cisco's IOS) do not use the
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DVMRP generation ID to determine that a neighbor has rebooted. Prunes
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sent towards these neighbors should be kept short, in order to shorten
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the time to recover from a reboot. For use in this situation, the
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prune_lifetime keyword may be specified on an interface as described
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below.
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.It noflood
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.Nm Mrouted
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uses a DVMRP optimization to prevent having to keep individual routing tables
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for each neighbor; part of this optimization is that
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.Nm
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assumes that it is the forwarder for each of its attached subnets on
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startup. This can cause duplicates for a short period (approximately
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one full route report interval), since both the router that just
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started up and the proper forwarder will be forwarding traffic. This
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behavior can be turned off with the noflood keyword;
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.Nm
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will not assume that it is the forwarder on startup.
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Turning on noflood can cause black holes on restart, which will generally
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last approximately one full route report interval.
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The noflood keyword can also be specified on individual interfaces.
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.It rexmit_prunes Ar [on|off]
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.Nm Mrouted 's
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default is to retransmit prunes on all point-to-point interfaces
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(including tunnels) but no multi-access interfaces. This option
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may be used to make the default on (or off) for all interfaces.
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The rexmit_prunes keyword can also be specified on individual interfaces.
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.It name Ar "boundary-name scoped-addr/mask-len"
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Associates
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.Ar boundary-name
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with the boundary described by
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.Ar scoped-addr/mask-len ,
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to help make interface configurations
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more readable and reduce repetition in the configuration file.
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.El
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.Pp
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The second section of the configuration file, which may optionally
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be empty, describes options that apply to physical interfaces.
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.Bl -tag -width indent
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.It phyint Ar "local-addr|ifname"
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The phyint command does nothing by itself; it is simply a place holder
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which interface-specific commands may follow. An interface address or
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name may be specified.
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.It disable
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Disables multicast forwarding on this interface. By default,
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.Nm
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discovers all locally attached multicast capable interfaces and forwards
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on all of them.
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.It netmask Ar netmask
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If the kernel's netmask does not accurately reflect
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the subnet (e.g. you're using proxy-ARP in lieu of IP subnetting), use the
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netmask command to describe the real netmask.
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.It altnet Ar network/mask-len
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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. This command may be specified multiple times
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to describe multiple subnets.
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.It igmpv1
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If there are any IGMPv1 routers on the phyint, use the \fBigmpv1\fP
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keyword to force
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.Nm
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into IGMPv1 mode. All routers on the phyint
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must use the same version of IGMP.
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.It force_leaf
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Force
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.Nm
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to ignore other routers on this interface.
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mrouted will never send or accept neighbor probes or
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route reports on this interface.
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.El
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.Pp
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In addition, the common vif commands described later may all be used on
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a phyint.
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.Pp
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The third section of the configuration file, also optional, describes
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the configuration of any DVMRP tunnels this router might have.
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.Bl -tag -width indent
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.It tunnel Ar "local-addr|ifname" Ar "remote-addr|remote-hostname"
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This command establishes a DVMRP tunnel between this host (on the interface
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described by
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.Ar local-addr
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or
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.Ar ifname )
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and a remote host (identified by
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.Ar remote-addr
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or
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.Ar remote-hostname ).
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A remote hostname may only be used if
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it maps to a single IP address.
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A tunnel must be configured on both routers before it can be used.
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Be careful that the unicast route to the remote address goes out the
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interface specified by the
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.Ar "local-addr|ifname"
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argument. Some UNIX
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kernels rewrite the source address of
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.Nm mrouted 's
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packets on their way out to contain the address of the transmission
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interface. This is best assured via a static host route.
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.El
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.Pp
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The common vif commands described below
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may all be used on tunnels or phyints.
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.Bl -tag -width indent
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.It metric Ar m
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The metric is the "cost" associated with receiving 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. Metrics should be kept as small as possible,
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because DVMRP cannot route along paths with a sum of metrics greater
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than 31.
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.It advert_metric Ar m
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The advert_metric is the "cost" associated with sending a datagram
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on the given interface or tunnel; it may be used to influence the choice
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of routes. The advert_metric defaults to 0. Note that the effective
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metric of a link is one end's metric plus the other end's advert_metric.
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.It threshold Ar t
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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. It is used to control the
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scope of multicast datagrams. (The TTL of forwarded packets is only compared
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to the threshold, it is not decremented by the threshold. Every multicast
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router decrements the TTL by exactly 1.) The default threshold is 1.
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In general, all multicast routers
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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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.It rate_limit Ar r
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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. It defaults 0 (unlimited).
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.It boundary Ar "boundary-name|scoped-addr/mask-len"
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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. Packets belonging to this address will not
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be forwarded on a scoped interface. The boundary option accepts either
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a name or a boundary spec. This command may be specified several times
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on an interface in order to describe multiple boundaries.
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.It passive
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No packets will be sent on this link or tunnel until we hear from the other
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end. This is useful for the "server" end of a tunnel that goes over
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a dial-on-demand link; configure the "server" end as passive and
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it will not send its periodic probes until it hears one from the other
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side, so will not keep the link up. If this option is specified on both
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ends of a tunnel, the tunnel will never come up.
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.It noflood
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As described above, but only applicable to this interface/tunnel.
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.It prune_lifetime Ar secs
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As described above, but only applicable to this interface/tunnel.
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.It rexmit_prunes Ar "[on|off]"
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As described above, but only applicable to this interface/tunnel.
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Recall that prune retransmission
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defaults to on on point-to-point links and tunnels, and off on
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multi-access links.
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.It allow_nonpruners
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By default,
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.Nm
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refuses to peer with DVMRP neighbors that
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do not claim to support pruning. This option allows such peerings
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on this interface.
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.It notransit
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A specialized case of route filtering; no route learned from an interface
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marked "notransit" will be advertised on another interface marked
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"notransit". Marking only a single interface "notransit" has no meaning.
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.It accept|deny Ar "(route/mask-len [exact])+" Op bidir
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The
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.Li accept
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and
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.Li deny
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commands allow rudimentary route filtering. The
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.Li accept
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command causes
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.Nm
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to accept only the listed routes on the configured interface; the
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.Li deny
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command causes
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.Nm
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to accept all but the listed routes.
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Only one of
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.Li accept
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or
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.Li deny
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commands may be used on a given interface.
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The list of routes follows the
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.Li accept
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or
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.Li deny
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keyword. If the keyword
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.Ar exact
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follows a route, then only that route is matched; otherwise, that route
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and any more specific route is matched. For example,
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.Li deny 0/0
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denys all routes, while
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.Li deny 0/0 exact
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denys only the default route. The default route may also be specified
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with the
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.Li default
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keyword.
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The
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.Ar bidir
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keyword enables bidirectional route filtering; the filter will be applied
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to routes on both output and input. Without the
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.Ar bidir
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keyword,
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.Li accept
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and
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.Li deny
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filters are only applied on input. Poison reverse routes are never
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filtered out.
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.El
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.Pp
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.Nm Mrouted
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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. It will log a warning if all of its vifs are
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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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.sp
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.nf
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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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.fi
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.Sh SIGNALS
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.Nm Mrouted
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responds to the following signals:
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.Bl -tag -width indent
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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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Terminate 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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Dump the internal routing tables to
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.Pa /var/tmp/mrouted.dump .
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.It USR2
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Dump the internal cache tables to
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.Pa /var/tmp/mrouted.cache .
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.It QUIT
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Dump 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 EXAMPLE
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The routing tables look like this:
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.nf
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.ft C
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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: 36.2/16 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: 36.11/16 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 (3.255)
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boundaries: 239.0.1/24
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: 239.1.2/24
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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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.fi
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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. The vif 3 tunnel is not in use (no peer address). The vif 0 and
|
|
vif 1 subnets have some groups present; tunnels never have any groups. This
|
|
instance of
|
|
.Nm
|
|
is the one responsible for sending periodic group
|
|
membership queries on the vif 0 and vif 1 subnets, as indicated by the
|
|
"querier" flags. The list of boundaries indicate the scoped addresses on that
|
|
interface. A count of the no. of incoming and outgoing packets is also
|
|
shown at each interface.
|
|
.Pp
|
|
Associated with each subnet from which a multicast datagram can originate
|
|
is the address of the previous hop router (unless the subnet is directly-
|
|
connected), the metric of the path back to the origin, the amount of time
|
|
since we last received an update for this subnet, the incoming vif for
|
|
multicasts from that origin, and a list of outgoing vifs. "*" means that
|
|
the outgoing vif is connected to a leaf of the broadcast tree rooted at the
|
|
origin, and a multicast datagram from that origin will be forwarded on that
|
|
outgoing vif only if there are members of the destination group on that leaf.
|
|
.Pp
|
|
.Nm Mrouted
|
|
also maintains a copy of the kernel forwarding cache table. Entries
|
|
are created and deleted by
|
|
.Nm mrouted .
|
|
.Pp
|
|
The cache tables look like this:
|
|
.nf
|
|
.ft C
|
|
|
|
Multicast Routing Cache Table (147 entries)
|
|
Origin Mcast-group CTmr Age Ptmr IVif Forwvifs
|
|
13.2.116/22 224.2.127.255 3m 2m - 0 1
|
|
>13.2.116.19
|
|
>13.2.116.196
|
|
138.96.48/21 224.2.127.255 5m 2m - 0 1
|
|
>138.96.48.108
|
|
128.9.160/20 224.2.127.255 3m 2m - 0 1
|
|
>128.9.160.45
|
|
198.106.194/24 224.2.135.190 9m 28s 9m 0P
|
|
>198.106.194.22
|
|
|
|
.fi
|
|
.Pp
|
|
Each entry is characterized by the origin subnet number and mask and the
|
|
destination multicast group.
|
|
.Pp
|
|
The 'CTmr' field indicates the lifetime
|
|
of the entry. The entry is deleted from the cache table
|
|
(or refreshed, if traffic is flowing)
|
|
when the timer decrements to zero. The 'Age' field is the time since
|
|
this cache entry was originally created. Since cache entries get refreshed
|
|
if traffic is flowing, routing entries can grow very old.
|
|
.Pp
|
|
The 'Ptmr' field is simply a dash if no prune was sent upstream, or the
|
|
amount of time until the upstream prune will time out.
|
|
.Pp
|
|
The 'Ivif' field indicates the
|
|
incoming vif for multicast packets from that origin. Each router also
|
|
maintains a record of the number of prunes received from neighboring
|
|
routers for a particular source and group. If there are no members of
|
|
a multicast group on any downward link of the multicast tree for a
|
|
subnet, a prune message is sent to the upstream router. They are
|
|
indicated by a "P" after the vif number.
|
|
.Pp
|
|
The Forwvifs field shows the
|
|
interfaces along which datagrams belonging to the source-group are
|
|
forwarded. A "p" indicates that no datagrams are being forwarded along
|
|
that interface. An unlisted interface is a leaf subnet with no
|
|
members of the particular group on that subnet. A "b" on an interface
|
|
indicates that it is a boundary interface, i.e. traffic will not be
|
|
forwarded on the scoped address on that interface.
|
|
.Pp
|
|
An additional line with a ">" as the first character is printed for
|
|
each source on the subnet. Note that there can be many sources in
|
|
one subnet.
|
|
An additional line with a "<" as the first character is printed
|
|
describing any prunes received from downstream dependent neighbors
|
|
for this subnet and group.
|
|
.Sh FILES
|
|
.Bl -tag -width /var/tmp/mrouted.cache -compact
|
|
.It Pa /etc/mrouted.conf
|
|
.It Pa /var/run/mrouted.pid
|
|
.It Pa /var/tmp/mrouted.dump
|
|
.It Pa /var/tmp/mrouted.cache
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr map-mbone 8 ,
|
|
.Xr mrinfo 8 ,
|
|
.Xr mtrace 8
|
|
.Pp
|
|
DVMRP is described, along with other multicast routing algorithms, in the
|
|
paper "Multicast Routing in Internetworks and Extended LANs" by S. Deering,
|
|
in the Proceedings of the ACM SIGCOMM '88 Conference.
|
|
.Sh AUTHORS
|
|
.An Steve Deering ,
|
|
.An Ajit Thyagarajan ,
|
|
.An Bill Fenner .
|