Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
MROUTED(8)		FreeBSD	System Manager's Manual		    MROUTED(8)

     mrouted --	IP multicast routing daemon

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

     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 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.	 Mrouted suffers from the well-known scaling problems
     of	any distance-vector routing protocol, and does not (yet) support hier-
     archical 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 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

     Mrouted automatically configures itself to	forward	on all multicast-capa-
     ble 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 config-
     uration, 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 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
	     Sepcifies,	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.

	     Mrouted uses a DVMRP optimization to prevent having to keep indi-
	     vidual routing tables for each neighbor; part of this optimiza-
	     tion 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 for-
	     warder 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]
	     Mrouted's 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	interfaces.

     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'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 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 on	point-to-point
	     links and tunnels,	and off	on 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.

     Mrouted 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

     Mrouted 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.

     Mrouted 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.	Deer-
     ing, in the Proceedings of	the ACM	SIGCOMM	'88 Conference.

     Steve Deering,
     Ajit Thyagarajan,
     Bill Fenner.

FreeBSD	11.1			  May 8, 1995			  FreeBSD 11.1


Want to link to this manual page? Use this URL:

home | help