320 lines
12 KiB
Groff
320 lines
12 KiB
Groff
'\"COPYRIGHT 1989 by The Board of Trustees of Leland Stanford Junior University.
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.TH MROUTED 8
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.UC 5
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.SH NAME
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mrouted \- IP multicast routing daemon
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.SH SYNOPSIS
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.B /etc/mrouted
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[
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.B \-p
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] [
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.B \-c
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.I config_file
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] [
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.B \-d
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[
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.I debug_level
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]]
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.SH DESCRIPTION
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.I 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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.I 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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.I mrouted
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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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.IR mrouted s
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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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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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.I mrouted
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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 supports IP source route tunnelling only for backwards
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compatibility.
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.PP
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The tunnelling mechanism allows
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.I mrouted
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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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.I 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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.I 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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.IR mrouted .
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With the use of tunnels, it
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is not necessary for
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.I mrouted
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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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.br
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.ne 5
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.SH INVOCATION
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.PP
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If no "\-d" option is given, or if the debug level is specified as 0,
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.I mrouted
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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. If "\-d" is
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given with no argument, the debug level defaults to 2. Regardless of the
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debug level,
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.I mrouted
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always writes warning and error messages to the system
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log demon. Non-zero debug levels have the following effects:
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.IP "level 1"
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all syslog'ed messages are also printed to stderr.
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.IP "level 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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.IP "level 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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.SH CONFIGURATION
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.PP
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.I 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
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.IR mrouted s
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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
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.IR mrouted s,
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configuration commands may be placed in
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/etc/mrouted.conf (or an alternative file, specified by the "\-c" option).
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There are four types of configuration commands:
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.nf
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phyint <local-addr> [disable] [metric <m>]
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[threshold <t>] [rate_limit <b>]
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[boundary <scoped-addr>/<mask-len>]
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tunnel <local-addr> <remote-addr> [metric <m>]
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[threshold <t>] [srcrt] [rate_limit <b>]
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[boundary <scoped-addr>/<mask-len>]
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cache_lifetime <ct>
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pruning <off/on>
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.fi
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.PP
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One note about the configuration commands - all the phyint and tunnel
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command options must be on a single line except for the boundary option
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which may begin on a separate line. A single phyint or tunnel command may
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have multiple boundary options.
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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 <local-addr>, or to associate a
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non-default metric or threshold with the specified physical interface.
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The local IP address <local-addr> may be alternatively replaced by the
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interface name (e.g le0) for the phyint command only.
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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 <local-addr> and remote IP address <remote-addr>, and to associate
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a non-default metric or threshold with that tunnel. The tunnel must be set
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up in the mrouted.conf files of both routers before 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. The value of this
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entry should lie between 300 (5 min) and 86400 (1 day). It defaults to 300.
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.PP
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The pruning <off/on> option is provided for
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.IR mrouted
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to act as a non-pruning router. It is also possible to start
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.Ir mrouted
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in a non-pruning mode using the "-p" option on the command line. It is
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expected that a router would be configured in this manner for test
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purposes only. The default mode is pruning enabled.
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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. Metrics should be kept as small as possible,
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because
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.I mrouted
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cannot route along paths with a sum of metrics greater
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than 31.
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.LP
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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 1.) The default threshold is 1.
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.LP
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In general, all
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.IR mrouted s
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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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.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. Packets belonging to this address will not
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be forwarded on a scoped interface.
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.PP
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.I 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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.I mrouted
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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 SIGNALS
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.PP
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.I Mrouted
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responds to the following signals:
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.IP HUP
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restarts
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.I mrouted .
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The configuration file is reread every time this signal is evoked.
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.IP 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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.IP TERM
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same as INT
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.IP USR1
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dumps the internal routing tables to /usr/tmp/mrouted.dump.
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.IP USR2
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dumps the internal cache tables to /usr/tmp/mrouted.cache.
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.IP QUIT
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dumps the internal routing tables to stderr (only if
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.I mrouted
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was invoked with a non-zero debug level).
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.bp
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.SH EXAMPLE
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.PP
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The routing tables look like this:
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.nf
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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 In-Vif Out-Vifs
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36.2 1 0 1* 2 3*
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36.8 36.8.0.77 4 2 0* 1* 3*
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36.11 1 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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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
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vif 1 subnets have some groups present; tunnels never have any groups. This
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instance of
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.I mrouted
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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. The list of boundaries indicate the scoped addresses on that
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interface. A count of the no. 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 incoming vif for
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multicasts from that origin, and a list of outgoing vifs. "*" 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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.bp
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.PP
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.I Mrouted
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also maintains a copy of the kernel forwarding cache table. Entries
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are created and deleted by
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.I mrouted.
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.PP
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The cache tables look like this:
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.nf
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Multicast Routing Cache Table (325 entries)
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Origin-Subnet Mcast-group CTmr IVif Prcv# Psnt Forwvifs
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134.207.7 224.2.140.239 300 1 0 0 2
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138.15.103 224.2.203.214 295 1 2 P 0p 2p
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128.237.0 224.2.253.119 290 1 1 0 2p
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129.215.200 224.2.207.48 40 1 1 0p 2
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36.77.14 239.0.1.234 345 2b
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.fi
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Each entry is characterized by the origin subnet number and the
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destination multicast group. The 'CTmr' field indicates the lifetime
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(in seconds) of the entry. The entry is deleted from the cache table
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when the timer decrements to zero. The Ivif field indicates the
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incoming vif for multicast packets from that origin. Each router also
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maintains a record of the number of prunes received from neighbouring
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routers for a particular source and group. 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. They are
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indicated by a "P" in the Psnt field. The Forwvifs field shows the
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interfaces along which datagrams belonging to the source-group are
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forwarded. A "p" indicates that no datagrams are being forwarded along
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that interface. An unlisted interface is a leaf subnet with are no
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members of the particular group on that subnet. 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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.SH FILES
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/etc/mrouted.conf
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.SH SEE ALSO
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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
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