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MROUTED(1M)							   MROUTED(1M)

NAME    [Toc]    [Back]

     mrouted - IP multicast routing daemon

SYNOPSIS    [Toc]    [Back]

     /usr/etc/mrouted [	-p ] [ -c config_file ]	[ -d [ debug_level ] ]

DESCRIPTION    [Toc]    [Back]

     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 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 also be used to limit its

     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.  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.	 This
     capability	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
     hierarchical multicast routing or inter-operation with other multicast
     routing protocols.

     Mrouted handles multicast routing only; there may or may not be unicast
     routing software running on the same machine as mrouted.  For example, an
     Internet unicast firewall can function as a multicast router.  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.

INVOCATION    [Toc]    [Back]

     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

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MROUTED(1M)							   MROUTED(1M)

     terminal.	If "-d"	is given 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:

     level 1
	  all syslog'ed	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 /etc/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"), and it 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; whitespace (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 alternatively

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MROUTED(1M)							   MROUTED(1M)

     replaced by the interface name (e.g., ec0).  If a phyint is attached to
     multiple IP subnets, describe each	additional subnet with the altnet
     keyword.  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 (e.g.,
     ec0).  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.

     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 pruning <off/on> option is provided for mrouted to act	as a nonpruning
 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 keyword.  The	boundary option	on phyint or tunnel commands can
     accept either a name or a boundary.

     The 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 metric	defaults to 1 and you do not normally need to use a different
     value.  There is no reason	to use a metric	greater	than 1 for any tunnel
     that is the only path to a	sub-cluster of tunnels and subnets.  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.  You need to use this parameter only if you want to
     prevent ``local'' multicast traffic from traversing a link.  Suggested
     Internet thresholds:

     32	  for links that separate sites	within an organization.

     64	  for links that separate communities or organizations,	and are
	  attached to the Internet MBONE.

									Page 3

MROUTED(1M)							   MROUTED(1M)

     128  for links that separate continents on	the MBONE.

     For example, if the networks in sites A and B are connected by a tunnel
     with a threshold of 8, then site-specific multicast datagrams should use
     a TTL of 7	to avoid traversing the	tunnel.

     All mrouteds connected to a particular subnet or tunnel should use	the
     same metric and threshold for that	subnet or tunnel to avoid connections
     that only work in one direction.

     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 5Mbps on physical
     interfaces. Set it	to zero	(0) to mean unlimited.

     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.

     Here are some reasons why multicast datagrams may fail to traverse	a
     tunnel, even though mrouted is properly exchanging	routes (i.e., shows
     lots of entries in	response to kill -USR1):

     o programs	use a TTL that is too small for	the tunnel threshold (as
       configured at the tunnel	entry).

     o there's a filtering router in the tunnel	path that selectively discards
       some IP datagrams such as IGMP packets or IP-over-IP encapsulated
       multicast data packets.

     o the two ends of tunnel are misconfigured, disagreeing on	tunnel type
       (encapsulating vs. source routing).

     Mrouted will not initiate execution if it has fewer than two enabled
     vifs, where a vif (virtual	interface) 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 (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
	  # xpi0 is our	gateway	to compsci, don't forward our

									Page 4

MROUTED(1M)							   MROUTED(1M)

	  #	local groups to	them
	  phyint xpi0 boundary EE
	  # xpi1 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).

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

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

EXAMPLE    [Toc]    [Back]

     The command

	  /sbin/killall	-USR1 mrouted

     dumps the routing tables to /var/tmp/mrouted.dump,	which looks like this:

	  Virtual Interface Table
	   Vif	Local-Address			 Metric	 Thresh	 Flags
	    0      subnet: 36.2	    1	    1	 querier

									Page 5

MROUTED(1M)							   MROUTED(1M)

			     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 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:

									Page 6

MROUTED(1M)							   MROUTED(1M)

	  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 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 are 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.

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

     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

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MROUTED(1M)							   MROUTED(1M)

NOTES    [Toc]    [Back]

     By	default, mrouted and its kernel	module is not loaded on	new systems.
     You may need to explicitly	install	the eoe.sw.ipgate subsystem in the
     IRIX distribution to load it.  After you install that subsystem, you will
     need to do	these commands as root:

	  # autoconfig
	  # chkconfig mrouted on
	  # reboot

     to	perform	multicast routing.

     If	you configure your machine to run mrouted and it is connected to a
     network having MBONE connectivity or if you create	a tunnel to a MBONEconnected
 machine,	please make sure you have the latest mrouted software.
     Consult ftp://ftp.sgi.com/sgi/ipmcast/README for information on
     availability of updated mrouted software.

     Older versions of mrouted (such as	the version in IRIX 3.3	and 4.0.x)
     encapsulate using IP source routing, which	puts a heavy load on some
     types of routers.	This version does not support IP source	route

     mrouted is	only capable of	supporting 32 multicast	interfaces.

									PPPPaaaaggggeeee 8888
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