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

     mrouted -- IP multicast routing daemon

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

     The mrouted utility 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 rout-
     ing protocol (like RIP, described in RFC-1058), upon which it implements
     a multicast datagram forwarding algorithm called Reverse Path Multicast-

     The mrouted utility forwards a multicast datagram along a shortest
     (reverse) path tree rooted at the subnet on which the datagram origi-
     nates.  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 multicast routers 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.  The packets are encapsulated using the IP-in-IP protocol
     (IP protocol number 4).  Older versions of mrouted tunneled using 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
     only, pending widespread support for multicast routing by the regular
     (unicast) routers.  The mrouted utility suffers from the well-known scal-
     ing problems of any distance-vector routing protocol, and does not (yet)
     support hierarchical multicast routing.

     The mrouted utility 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 following options are available:

     -c config_file
             Specify an alternative file for configuration commands.  Default
             is /etc/mrouted.conf.

     -d [debug_level]
             If no -d option is given, 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 sig-
             nals from that terminal.  Regardless of the debug level, mrouted
             always writes warning and error messages to the system log dae-
             mon.  The -debug-level argument is a comma-separated list of any
             of the following:

             packet  Display the type, source and destination of all packets
                     sent or received.

                     Display more information about prunes sent or received.

                     Display more information about routing update packets
                     sent or received.

                     Display routing updates in excruciating detail.  This is
                     generally way too much information.

                     Display information about neighbor discovery.

             cache   Display insertions, deletions and refreshes of entries in
                     the kernel forwarding cache.

                     Debug timeouts and periodic processes.

                     Display information about interfaces and their configura-

                     Display information about group memberships on physical

                     Display information about multicast traceroute requests
                     passing through this router.

             igmp    Display IGMP operation including group membership and
                     querier election.

             icmp    Monitor ICMP handling.

             rsrr    Monitor RSRR operation.

             Upon startup, mrouted writes its pid to the file

     The mrouted utility automatically configures itself to forward on all
     multicast-capable interfaces, i.e., interfaces that have the IFF_MULTI-
     CAST flag set (excluding the loopback "interface"), and it finds other
     DVMRP routers directly reachable via those interfaces.  To override the
     default configuration, or to add tunnel links to other multicast routers,
     configuration commands may be placed in /etc/mrouted.conf (or an alterna-
     tive file, specified by the -c option).

     The file format is free-form; whitespace (including newlines) is not sig-
     nificant.  The file begins with commands that apply to mrouted's overall
     operation or set defaults.

     cache_lifetime secs
             Specifies, in seconds, the lifetime of a multicast forwarding
             cache entry in the kernel.  Multicast forwarding cache entries in
             the kernel are checked every secs seconds, and are refreshed if
             the source is still active or deleted if not.  Care should be
             taken when setting this value, as a low value can keep the kernel
             cache small at the cost of "thrashing" the cache for periodic
             senders, but high values can cause the kernel cache to grow unac-
             ceptably large.  The default is 300 seconds (5 minutes).

     prune_lifetime secs
             Specifies, in seconds, the average lifetime of prunes that are
             sent towards parents.  The actual lifetimes will be randomized in
             the range [.5secs,1.5secs].  The default is 7200 (2 hours).
             Smaller values cause less state to be kept both at this router
             and the parent, at the cost of more frequent broadcasts.  How-
             ever, some routers (e.g. mrouted <3.3 and all currently known
             versions of cisco's IOS) do not use the DVMRP generation ID to
             determine that a neighbor has rebooted.  Prunes sent towards
             these neighbors should be kept short, in order to shorten the
             time to recover from a reboot.  For use in this situation, the
             prune_lifetime keyword may be specified on an interface as
             described below.

             The mrouted utility uses a DVMRP optimization to prevent having
             to keep individual routing tables for each neighbor; part of this
             optimization is that mrouted assumes that it is the forwarder for
             each of its attached subnets on startup.  This can cause dupli-
             cates for a short period (approximately one full route report
             interval), since both the router that just started up and the
             proper forwarder will be forwarding traffic.  This behavior can
             be turned off with the noflood keyword; mrouted will not assume
             that it is the forwarder on startup.  Turning on noflood can
             cause black holes on restart, which will generally last approxi-
             mately one full route report interval.  The noflood keyword can
             also be specified on individual interfaces.

     rexmit_prunes [on|off]
             Default is to retransmit prunes on all point-to-point interfaces
             (including tunnels) but no multi-access interfaces.  This option
             may be used to make the default on (or off) for all interfaces.
             The rexmit_prunes keyword can also be specified on individual

     name boundary-name scoped-addr/mask-len
             Associates boundary-name with the boundary described by
             scoped-addr/mask-len, to help make interface configurations more
             readable and reduce repetition in the configuration file.

     The second section of the configuration file, which may optionally be
     empty, describes options that apply to physical interfaces.

     phyint local-addr|ifname
             The phyint command does nothing by itself; it is simply a place
             holder which interface-specific commands may follow.  An inter-
             face address or name may be specified.

             Disables multicast forwarding on this interface.  By default,
             mrouted discovers all locally attached multicast capable inter-
             faces and forwards on all of them.

     netmask netmask
             If the kernel's netmask does not accurately reflect the subnet
             (e.g. you are using proxy-ARP in lieu of IP subnetting), use the
             netmask command to describe the real netmask.

     altnet network/mask-len
             If a phyint is attached to multiple IP subnets, describe each
             additional subnet with the altnet keyword.  This command may be
             specified multiple times to describe multiple subnets.

     igmpv1  If there are any IGMPv1 routers on the phyint, use the igmpv1
             keyword to force mrouted into IGMPv1 mode.  All routers on the
             phyint must use the same version of IGMP.

             Force mrouted to ignore other routers on this interface.  mrouted
             will never send or accept neighbor probes or route reports on
             this interface.

     In addition, the common vif commands described later may all be used on a

     The third section of the configuration file, also optional, describes the
     configuration of any DVMRP tunnels this router might have.

     tunnel local-addr|ifname remote-addr|remote-hostname
             This command establishes a DVMRP tunnel between this host (on the
             interface described by local-addr or ifname) and a remote host
             (identified by remote-addr or remote-hostname).  A remote host-
             name may only be used if it maps to a single IP address.  A tun-
             nel must be configured on both routers before it can be used.

             Be careful that the unicast route to the remote address goes out
             the interface specified by the local-addr|ifname argument.  Some
             UNIX kernels rewrite the source address of mrouted's packets on
             their way out to contain the address of the transmission inter-
             face.  This is best assured via a static host route.

     The common vif commands described below may all be used on tunnels or

     metric m
             The metric is the "cost" associated with receiving 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 DVMRP cannot route along paths
             with a sum of metrics greater than 31.

     advert_metric m
             The advert_metric is the "cost" associated with sending a data-
             gram on the given interface or tunnel; it may be used to influ-
             ence the choice of routes.  The advert_metric defaults to 0.
             Note that the effective metric of a link is one end's metric plus
             the other end's advert_metric.

     threshold t
             The threshold is the minimum IP time-to-live required for a mul-
             ticast 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 exactly 1.)  The default threshold is 1.

             In general, all multicast routers connected to a particular sub-
             net or tunnel should use the same metric and threshold for that
             subnet or tunnel.

     rate_limit r
             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 0 (unlimited).

     boundary boundary-name|scoped-addr/mask-len
             The boundary option allows an interface to be configured as an
             administrative boundary for the specified scoped address.  Pack-
             ets belonging to this address will not be forwarded on a scoped
             interface.  The boundary option accepts either a name or a bound-
             ary spec.  This command may be specified several times on an
             interface in order to describe multiple boundaries.

             No packets will be sent on this link or tunnel until we hear from
             the other end.  This is useful for the "server" end of a tunnel
             that goes over a dial-on-demand link; configure the "server" end
             as passive and it will not send its periodic probes until it
             hears one from the other side, so will not keep the link up.  If
             this option is specified on both ends of a tunnel, the tunnel
             will never come up.

             As described above, but only applicable to this interface/tunnel.

     prune_lifetime secs
             As described above, but only applicable to this interface/tunnel.

     rexmit_prunes [on|off]
             As described above, but only applicable to this interface/tunnel.
             Recall that prune retransmission defaults to on for point-to-
             point links and tunnels, and to off for multi-access links.

             By default, mrouted refuses to peer with DVMRP neighbors that do
             not claim to support pruning.  This option allows such peerings
             on this interface.

             A specialized case of route filtering; no route learned from an
             interface marked "notransit" will be advertised on another inter-
             face marked "notransit".  Marking only a single interface
             "notransit" has no meaning.

     accept|deny (route/mask-len [exact])+ [bidir]
             The accept and deny commands allow rudimentary route filtering.
             The accept command causes mrouted to accept only the listed
             routes on the configured interface; the deny command causes
             mrouted to accept all but the listed routes.  Only one of accept
             or deny commands may be used on a given interface.

             The list of routes follows the accept or deny keyword.  If the
             keyword exact follows a route, then only that route is matched;
             otherwise, that route and any more specific route is matched.
             For example, deny 0/0 denys all routes, while deny 0/0 exact
             denys only the default route.  The default route may also be
             specified with the default keyword.

             The bidir keyword enables bidirectional route filtering; the fil-
             ter will be applied to routes on both output and input.  Without
             the bidir keyword, accept and deny filters are only applied on
             input.  Poison reverse routes are never filtered out.

     The mrouted utility will not initiate execution if it has fewer than two
     enabled vifs, where a vif (virtual interface) is either a physical multi-
     cast-capable 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).

     This is an example configuration for a mythical multicast router at a big

     # mrouted.conf example
     # Name our boundaries to make it easier
     name LOCAL
     name EE
     # 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 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

     The mrouted utility responds to the following signals:

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

     INT     Terminate execution gracefully (i.e., by sending good-bye mes-
             sages to all neighboring routers).

     TERM    Same as INT.

     USR1    Dump the internal routing tables to /var/tmp/mrouted.dump.

     USR2    Dump the internal cache tables to /var/tmp/mrouted.cache.

     QUIT    Dump 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/run/ upon startup.


     The routing tables look like this:

     Virtual Interface Table
      Vif  Local-Address                    Metric  Thresh  Flags
       0      subnet: 36.2/16       1       1    querier
                        pkts in: 3456
                       pkts out: 2322323

       1     subnet: 36.11/16      1       1    querier
                        pkts in: 345
                       pkts out: 3456

       2      tunnel:     3       1
                          peers: (3.255)
                     boundaries: 239.0.1/24
                               : 239.1.2/24
                        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 no.  of incoming 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 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.

     The mrouted utility 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 and mask and the
     destination multicast group.

     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.

     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, 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.
     An additional line with a "<" as the first character is printed describ-
     ing any prunes received from downstream dependent neighbors for this sub-
     net and group.

     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.
     Deering, in the Proceedings of the ACM SIGCOMM '88 Conference.

     Steve Deering,
     Ajit Thyagarajan,
     Bill Fenner.

FreeBSD 6.2                       May 8, 1995                      FreeBSD 6.2


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