MROUTED(8)              OpenBSD System Manager's Manual             MROUTED(8)

NAME
     mrouted - IP multicast routing daemon

SYNOPSIS
     mrouted [-p] [-c config_file] [-d [debug_level]]

DESCRIPTION
     mrouted 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 multi-
     cast 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 mrouted daemons 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).  Older versions of mrouted tunnel use
     IP source routing, which puts a heavy load on some types of routers.
     This version does not support IP source route tunnelling.

     The tunnelling mechanism allows mrouted to establish a virtual internet,
     for the purpose of multicasting only, which is independent of the physi-
     cal internet, and which may span multiple Autonomous Systems.  This capa-
     bility is intended for experimental support of internet multicasting on-
     ly, pending widespread support for multicast routing by the regular (uni-
     cast) routers.  mrouted suffers from the well-known scaling problems of
     any distance-vector routing protocol, and does not (yet) support hierar-
     chical multicast routing.

     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 forwarding.

     The options are as follows:

     -c config_file
             Specify an alternative configuration file, instead of the default
             mrouted.conf.

     -d [debug_level]
             By default, mrouted detaches from the invoking terminal.  If this
             option is specified, mrouted remains attached to the invoking
             terminal and responsive to signals from that terminal.  If -d is
             given with no argument, the debug level defaults to 2.  Regard-
             less of the debug level, mrouted always writes warning and error
             messages to the system log daemon.  Debug levels have the follow-
             ing effects:

                   0       Detach from the invoking terminal.
                   1       All syslog(3) messages are also printed to stderr.
                   2       All level 1 messages plus notifications of "signif-
                           icant" events are printed to stderr.
                   3       All level 2 messages plus notifications of all
                           packet arrivals and departures are printed to
                           stderr.

     -p      Start mrouted in a non-pruning mode.  It is expected that a
             router would be configured in this manner for test purposes only.
             The default mode is pruning enabled.

     mrouted automatically configures itself to forward on all multicast-capa-
     ble interfaces, i.e. interfaces that have the IFF_MULTICAST flag set (ex-
     cluding the loopback "interface"), and it finds other mrouted directly
     reachable via those interfaces.  To override the default configuration,
     or to add tunnel links to other mrouted, configuration commands may be
     placed in /etc/mrouted.conf.  There are five types of configuration com-
     mands:

           cache_lifetime ct

           name boundary-name | scoped-addr/mask-len

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

           pruning [off | on]

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

     The file format is free-form: whitespace (including newlines) is not sig-
     nificant.  The boundary option can accept either a name or a boundary;
     the boundary and altnet options may be specified as many times as neces-
     sary.

     The 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 name option assigns names to boundaries to make configuration easier.

     The phyint command can be used to disable multicast routing on the physi-
     cal 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
     (e.g. le0).  If a phyint is attached to multiple IP subnets, describe
     each additional subnet with the altnet keyword.  Phyint commands must
     precede tunnel commands.

     The pruning option is provided for mrouted to act as a non-pruning
     router.

     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 (e.g. le0).  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.

     boundary allows an interface to be configured as an administrative bound-
     ary 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.

     metric is the "cost" associated with sending a datagram on the given in-
     terface 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, be-
     cause mrouted cannot route along paths with a sum of metrics greater than
     31.

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

     threshold is the minimum IP time-to-live required for a multicast data-
     gram 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 thresh-
     old.  Every multicast router decrements the TTL by 1.)  The default
     threshold is 1.

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

     mrouted will not initiate execution if it has fewer than two enabled vir-
     tual interfaces (vifs), where a vif is either a physical multicast-capa-
     ble 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 (i.e. eliminate the middle man).

EXAMPLE CONFIGURATION
     This is an example configuration for a mythical multicast router at a big
     school.

     #
     # mrouted.conf example
     #
     # Name our boundaries to make it easier.
     name LOCAL 239.255.0.0/16
     name EE 239.254.0.0/16
     #
     # le1 is our gateway to compsci, don't forward our
     # local groups to them.
     phyint le1 boundary EE
     #
     # le2 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 172.16.12.38 boundary EE altnet 172.16.15.0/26
          altnet 172.16.15.128/26 altnet 172.16.48.0/24
     #
     # 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 192.168.5.4 192.168.55.101 metric 1 threshold 1
          rate_limit 0
     #
     # This is our tunnel to the outside world.
     # Careful with those boundaries, Eugene.
     tunnel 192.168.5.4 10.11.12.13 metric 1 threshold 32
          boundary LOCAL boundary EE

SIGNALS
     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  The same as INT.
     USR1  Dumps the internal routing tables to /var/tmp/mrouted.dump.
     USR2  Dumps the internal cache tables to /var/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 process ID to
     /var/run/mrouted.pid upon startup.

FILES
     /etc/mrouted.conf
     /var/tmp/mrouted.cache
     /var/tmp/mrouted.dump
     /var/run/mrouted.pid

EXAMPLES
     The routing tables look like this:

     Virtual Interface Table
      Vif  Local-Address                    Metric  Thresh  Flags
       0   36.2.0.8      subnet: 36.2          1       1    querier
                         groups: 224.0.2.1
                                 224.0.0.4
                        pkts in: 3456
                       pkts out: 2322323

       1   36.11.0.1     subnet: 36.11         1       1    querier
                         groups: 224.0.2.1
                                 224.0.1.0
                                 224.0.0.4
                        pkts in: 345
                       pkts out: 3456

       2   36.2.0.8      tunnel: 36.8.0.77     3       1
                          peers: 36.8.0.77 (2.2)
                     boundaries: 239.0.1
                               : 239.1.2
                        pkts in: 34545433
                       pkts out: 234342

       3   36.2.0.8     tunnel: 36.6.8.23      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            36.8.0.77          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 pe-
     riodic group membership queries on the vif 0 and vif 1 subnets, as indi-
     cated by the "querier" flags.  The list of boundaries indicate the scoped
     addresses on that interface.  A count of the number of incoming and out-
     going 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 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.

     mrouted also maintains a copy of the kernel forwarding cache table.  En-
     tries 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        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

     Each entry is characterized by the origin subnet number and 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 up-
     stream 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" af-
     ter 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 in-
     terface, i.e. 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.

SEE ALSO
     map-mbone(8), mrinfo(8), mtrace(8)

     DVMRP is described, along with other multicast routing algorithms, in the
     paper "Multicast Routing in Internetworks and Extended LANs" by S. Deer-
     ing, in the Proceedings of the ACM SIGCOMM '88 Conference.

AUTHORS
     Steve Deering, Ajit Thyagarajan, Bill Fenner

OpenBSD 4.7                     January 6, 2010                              5
