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 mrouted(1M)                                                     mrouted(1M)

 NAME    [Toc]    [Back]
      mrouted - IP multicast routing daemon

 SYNOPSIS    [Toc]    [Back]
      /usr/sbin/mrouted [-p] [-c config_file] [-d debug_level]

 DESCRIPTION    [Toc]    [Back]
      The mrouted command is an implementation of the Distance-Vector
      Multicast Routing Protocol (DVMRP), an earlier version of which is
      specified in RFC-1075.  It maintains topological knowledge via a
      distance-vector routing protocol (like RIP, described in RFC-1058),
      upon which it implements a multicast datagram-forwarding algorithm
      called Reverse Path Multicasting.

      mrouted forwards a multicast datagram along a shortest (reverse) path
      tree rooted at the subnet on which the datagram originates. The
      multicast delivery tree may be thought of as a broadcast delivery tree
      that has been pruned back so that it does not extend beyond those
      subnetworks that have members of the destination group. Hence,
      datagrams are not forwarded along those branches which have no
      listeners of the multicast group. The IP time-to-live of a multicast
      datagram can be used to limit the range of multicast datagrams.

      In order to support multicasting among subnets that are separated by
      (unicast) routers that do not support IP multicasting, mrouted
      includes support for "tunnels", which are virtual point-to-point links
      between pairs of mrouteds located anywhere in an internet.  IP
      multicast packets are encapsulated for transmission through tunnels,
      so that they look like normal unicast datagrams to intervening routers
      and subnets.  The encapsulation is added on entry to a tunnel and
      stripped off on exit from a tunnel.  By default, the packets are
      encapsulated using the IP-in-IP protocol (IP protocol number 4).

      The tunnelling mechanism allows mrouted to establish a virtual
      internet for the purpose of multicasting only, which is independent of
      the physical internet and which may span multiple Autonomous Systems.

      mrouted handles multicast routing only; there may or may not be
      unicast routing software running on the same machine as mrouted.  With
      the use of tunnels, it is not necessary for mrouted to have access to
      more than one physical subnet in order to perform multicast

    Invocation    [Toc]    [Back]
      If the -d option is not specified or if the debug level is specified
      as 0, mrouted detaches from the invoking terminal.  Otherwise, it
      remains attached to the invoking terminal and responsive to signals
      from that terminal. If -d is specified with no argument, the debug
      level defaults to 2. Regardless of the debug level, mrouted always
      writes warning and error messages to the system log demon.  Non-zero
      debug levels have the following effects:

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 mrouted(1M)                                                     mrouted(1M)

      level 1   all syslog messages are also printed to stderr.

      level 2   all level 1 messages plus notifications of "significant"
                events are printed to stderr.

      level 3   all level 2 messages plus notifications of all packet
                arrivals and departures are printed to stderr.

      Upon startup, mrouted writes its pid to the file /var/tmp/mrouted.pid.

    Configuration    [Toc]    [Back]
      mrouted automatically configures itself to forward on all multicastcapable
 interfaces (i.e., interfaces that have the IFF_MULTICAST flag
      set, excluding the loopback "interface"). mrouted finds other mrouteds
      directly reachable via those interfaces.  To override the default
      configuration or to add tunnel links to other mrouteds, configuration
      commands may be placed in /etc/mrouted.conf (or an alternative file,
      specified by the -c option).  There are four types of configuration

               phyint <local-addr>   [disable]   [metric <m>]
                      [threshold <t>] [rate_limit <b>]
                        [boundary (<boundary-name>|<scoped-addr>/<mask-len>)]
                        [altnet <network>/<mask-len>]

               tunnel <local-addr> <remote-addr> [metric <m>]
                      [threshold <t>] [rate_limit <b>]
                        [boundary (<boundary-name>|<scoped-addr>/<mask-len>)]

               cache_lifetime <ct>

               pruning <off/on>

               name <boundary-name> <scoped-addr>/<mask-len>

      The file format is free-form; white space (including newlines) is not
      significant.  The boundary and altnet options may be specified as many
      times as necessary.

      The phyint command can be used to disable multicast routing on the
      physical interface identified by local IP address <local-addr>, or to
      associate a non-default metric or threshold with the specified
      physical interface.  The local IP address <local-addr> may be replaced
      by the interface name (such as lan0 ).  If phyint is attached to
      multiple IP subnets, describe each additional subnet with the altnet
      option.  phyint commands must precede tunnel commands.

      The tunnel command can be used to establish a tunnel link between
      local IP address <local-addr> and remote IP address <remote-addr>, and
      to associate a non-default metric or threshold with that tunnel.  The
      local IP address <local-addr> may be replaced by the interface name

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 mrouted(1M)                                                     mrouted(1M)

      (such as lan0 ).  The remote IP address <remote-addr> may be replaced
      by a host name, if and only if the host name has a single IP address
      associated with it.  The tunnel must be set up in the mrouted.conf
      files of both routers before it can be used.

      cache_lifetime is a value that determines the amount of time that a
      cached multicast route stays in kernel before timing out. The value of
      this entry should lie between 300 (5 min) and 86400 (1 day). It
      defaults to 300.

      The pruning command is provided for mrouted to act as a non-pruning
      router. It is also possible to start mrouted in a non-pruning mode
      using the -p option on the command line. It is expected that a router
      would be configured in this manner for test purposes only. The default
      mode is pruning enabled.

      You may assign names to boundaries to make configuration easier with
      the name command.  The boundary option on phyint or tunnel commands
      can accept either a name or a boundary.

      The metric option is the "cost" associated with sending a datagram on
      the given interface or tunnel; it may be used to influence the choice
      of routes.  The metric defaults to 1.  Metrics should be kept as small
      as possible because mrouted cannot route along paths with a sum of
      metrics greater than 31.

      The threshold is the minimum IP time-to-live required for a multicast
      datagram to be forwarded to the given interface or tunnel.  It is used
      to control the scope of multicast datagrams.  (The TTL of forwarded
      packets is only compared to the threshold; it is not decremented by
      the threshold.  Every multicast router decrements the TTL by 1.)  The
      default threshold is 1.

      In general, all mrouteds connected to a particular subnet or tunnel
      should use the same metric and threshold for that subnet or tunnel.

      The rate_limit option allows the network administrator to specify a
      certain bandwidth in Kbits/second which would be allocated to
      multicast traffic.  It defaults to 500Kbps on tunnels and 0
      (unlimited) on physical interfaces.

      The boundary option allows an interface to be configured as an
      administrative boundary for the specified scoped address. Packets
      belonging to this address will not be forwarded on a scoped interface.
      The boundary option accepts either a name or a boundary spec.

      mrouted will not initiate execution if it has fewer than two enabled
      vifs (virtual interface), where a vif is either a physical multicastcapable
 interface or a tunnel.  It will log a warning if all of its
      vifs are tunnels; such an mrouted configuration would be better
      replaced by more direct tunnels.

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 mrouted(1M)                                                     mrouted(1M)

    Example Configuration    [Toc]    [Back]
      This is an example configuration for a multicast router at a large

           # mrouted.conf example
           # Name our boundaries to make it easier
           name LOCAL
           name EE
           # lan1 is our gateway to compsci, don't forward our
           # local groups to them
           phyint lan1 boundary EE
           # lan2 is our interface on the classroom net, it has four
           # different length subnets on it.
           # note that you can use either an ip address or an
           # interface name
           phyint boundary EE altnet
                altnet altnet
           # atm0 is our ATM interface, which doesn't properly
           # support multicasting.
           phyint atm0 disable
           # This is an internal tunnel to another EE subnet
           # Remove the default tunnel rate limit, since this
           # tunnel is over ethernets
           tunnel metric 1 threshold 1
                rate_limit 0
           # This is our tunnel to the outside world.
           # Careful with those boundaries, Eugene.
           tunnel metric 1 threshold 32
                boundary LOCAL boundary EE

    Signals    [Toc]    [Back]
      mrouted responds to the following signals:

      HUP       restarts mrouted.  The configuration file is reread every
                time this signal is evoked.

      INT       terminates execution gracefully (i.e., by sending good-bye
                messages to all neighboring routers).

      TERM      same as INT

      USR1      dumps the internal routing tables to /usr/tmp/mrouted.dump.

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 mrouted(1M)                                                     mrouted(1M)

      USR2      dumps the internal cache tables to /usr/tmp/mrouted.cache.

      QUIT      dumps the internal routing tables to stderr (only if mrouted
                was invoked with a non-zero debug level).

      For convenience in sending signals, mrouted writes its pid to
      /var/tmp/mrouted.pid upon startup.

 EXAMPLES    [Toc]    [Back]
      The routing tables look like this:

           Virtual Interface Table
            Vif  Local-Address                    Metric  Thresh  Flags
             0      subnet: 36.2          1       1    querier
                              pkts in: 3456
                             pkts out: 2322323

             1     subnet: 36.11         1       1    querier
                              pkts in: 345
                             pkts out: 3456

             2      tunnel:     3       1
                                peers: (2.2)
                           boundaries: 239.0.1
                                     : 239.1.2
                              pkts in: 34545433
                             pkts out: 234342

             3     tunnel:      3       16

           Multicast Routing Table (1136 entries)
            Origin-Subnet   From-Gateway    Metric Tmr In-Vif  Out-Vifs
            36.2                               1    45    0    1* 2  3*
            36.8            4    15    2    0* 1* 3*
            36.11                              1    20    1    0* 2  3*

      In this example, there are four vifs connecting to two subnets and two
      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 mrouted 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 number of incoming

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 mrouted(1M)                                                     mrouted(1M)

      and outgoing packets is also shown at each interface.

      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 an update was received for this subnet, the
      incoming vif for multicasts from that origin, and a list of outgoing
      vifs.  The asterisk ( * ) indicates 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.

      The mrouted command also maintains a copy of the kernel forwarding
      cache table. Entries are created and deleted by mrouted.

      The cache tables look like this:

           Multicast Routing Cache Table (147 entries)
            Origin             Mcast-group     CTmr  Age Ptmr IVif Forwvifs
            13.2.116/22     3m   2m    -  0    1
            138.96.48/21     5m   2m    -  0    1
            128.9.160/20     3m   2m    -  0    1
            198.106.194/24     9m  28s   9m  0P

      Each entry is characterized by the origin subnet number, mask, and the
      destination multicast group. The CTmr field indicates the lifetime of
      the entry.  The entry is deleted from the cache table 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.  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.  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.  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; that is, traffic will not be
      forwarded on the scoped address on that interface.  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.

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 mrouted(1M)                                                     mrouted(1M)

 AUTHORS    [Toc]    [Back]
      Steve Deering, Ajit Thyagarajan, Bill Fenner.

 FILES    [Toc]    [Back]

 SEE ALSO    [Toc]    [Back]
      mrinfo(1M), map-mbone(1M).

      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.

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[ Back ]
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