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NAME    [Toc]    [Back]

     mrouted -- IP multicast routing daemon

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     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 routing
 protocol (like RIP, described in RFC-1058), upon which it implements
     a multicast datagram forwarding algorithm called Reverse Path Multicasting.

     The mrouted utility 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 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 physical
 internet, and which may span multiple Autonomous Systems.  This capability
 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 scaling
 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 signals
 from that terminal.  Regardless of the debug level, mrouted
	     always writes warning and error messages to the system log daemon.
  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 configuration.

		     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

CONFIGURATION    [Toc]    [Back]

     The mrouted utility automatically configures itself to forward on all
     multicast-capable interfaces, i.e., interfaces that have the IFF_MULTICAST
 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 alternative
 file, specified by the -c option).

     The file format is free-form; whitespace (including newlines) is not significant.
	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 unacceptably
 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.  However,
 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 duplicates
 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 approximately
 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 interface
 address or name may be specified.

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

     netmask netmask
	     If the kernel's netmask does not accurately reflect the subnet
	     (e.g. you're 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 hostname
 may only be used if it maps to a single IP address.  A tunnel
 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 interface.
  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 datagram
 on the given interface or tunnel; it may be used to influence
 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 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 exactly 1.)  The default threshold is 1.

	     In general, all multicast routers connected to a particular subnet
 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.	Packets
 belonging to this address will not be forwarded on a scoped
	     interface.  The boundary option accepts either a name or a boundary
 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-topoint
 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 interface
 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 filter
 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 multicast-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

SIGNALS    [Toc]    [Back]

     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 messages
 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/mrouted.pid upon startup.

EXAMPLES    [Toc]    [Back]

     The routing tables look like this:

     Virtual Interface Table
      Vif  Local-Address		    Metric  Thresh  Flags
       0	 subnet: 36.2/16       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 directlyconnected),
 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 describing
 any prunes received from downstream dependent neighbors for this subnet
 and group.

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

     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.

AUTHORS    [Toc]    [Back]

     Steve Deering,
     Ajit Thyagarajan,
     Bill Fenner.

FreeBSD 5.2.1			  May 8, 1995			 FreeBSD 5.2.1
[ Back ]
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