mrouted(8)

NAME

mrouted - IP multicast routing daemon

SYNOPSIS

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

DESCRIPTION

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 dis
tance-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 data
gram 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 sep
arated 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 vir
tual internet, for the purpose of multicasting only, which is independent
of the physical internet, and which may span multiple Autonomous Sys
tems. This capability is intended for experimental support of internet mul
ticasting 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 com; mands. 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 re; sponsive to signals from that terminal. Regardless of the debug; level, mrouted
always writes warning and error messages to the sys; tem 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.
pruning: Display more information about prunes sent; or received.
routing: Display more information about routing up; date packets
sent or received.
route_detail: Display routing updates in excruciating de; tail. This is
generally way too much information.
neighbors: Display information about neighbor discov; ery.
cache Display insertions, deletions and refreshes
of entries in: the kernel forwarding cache.
timeout: Debug timeouts and periodic processes.
interface: Display information about interfaces and; their configuration.
membership: Display information about group memberships; on physical
interfaces.
traceroute: Display information about multicast tracer; oute requests
passing through this router.
igmp Display IGMP operation including group mem
bership and: querier election.
icmp Monitor ICMP handling.
rsrr Monitor RSRR operation.
Upon startup, mrouted writes its pid to the file
/var/run/mrouted.pid.

CONFIGURATION

The mrouted utility automatically configures itself to for
ward 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 mul
ticast 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 new
lines) 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 min; utes).
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 broad; casts. However, some routers (e.g. mrouted <3.3 and all cur; rently known
versions of cisco's IOS) do not use the DVMRP gener; ation 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 sit; uation, the
prune_lifetime keyword may be specified on an inter; face as
described below.
noflood: 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
interfaces.
name boundary-name scoped-addr/mask-len: Associates boundary-name with the boundary described; by
scoped-addr/mask-len, to help make interface config; urations more
readable and reduce repetition in the configuration; file.
The second section of the configuration file, which may op
tionally 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.
disable: Disables multicast forwarding on this interface. By; default,
mrouted discovers all locally attached multicast ca; pable interfaces 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 subnet; ting), use the
netmask command to describe the real netmask.
altnet network/mask-len: If a phyint is attached to multiple IP subnets, de; scribe each
additional subnet with the altnet keyword. This; command may be
specified multiple times to describe multiple sub; nets.
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_leaf: Force mrouted to ignore other routers on this inter; face. 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 phyint.
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 ad; dress. A tunnel must be configured on both routers before it can; be used.; Be careful that the unicast route to the remote ad; dress goes out
the interface specified by the local-addr|ifname ar; gument. Some
UNIX kernels rewrite the source address of mrouted's; packets on
their way out to contain the address of the trans; mission interface. This is best assured via a static host route.
The common vif commands described below may all be used on
tunnels or phyints.
metric m: The metric is the "cost" associated with receiving a; datagram on
the given interface or tunnel; it may be used to in; fluence the
choice of routes. The metric defaults to 1. Met; rics 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 de; faults 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 re; quired for a multicast datagram to be forwarded to the given inter; face or tunnel.
It is used to control the scope of multicast data; grams. (The TTL
of forwarded packets is only compared to the thresh; old, 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 thresh; old for that
subnet or tunnel.
rate_limit r: The rate_limit option allows the network administra; tor 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 con; figured as an
administrative boundary for the specified scoped ad; dress. 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.
passive: 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.
noflood: As described above, but only applicable to this in; terface/tunnel.
prune_lifetime secs: As described above, but only applicable to this in; terface/tunnel.
rexmit_prunes [on|off]: As described above, but only applicable to this in; terface/tunnel.
Recall that prune retransmission defaults to on for; point-topoint links and tunnels, and to off for multi-access; links.
allow_nonpruners: By default, mrouted refuses to peer with DVMRP; neighbors that do
not claim to support pruning. This option allows; such peerings
on this interface.
notransit: 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 in; terface
"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 key; word. 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 fil; tering; the filter will be applied to routes on both output and in; put. 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).

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

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/mrouted.pid upon startup.

FILES

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

EXAMPLES

The routing tables look like this:

Virtual Interface Table: Vif Local-Address Metric Thresh Flags
0 36.2.0.8 subnet: 36.2/16 1 1

querier
groups: 224.0.2.1
224.0.0.4

pkts in: 3456

pkts out: 2322323
1 36.11.0.1 subnet: 36.11/16 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 (3.255)
boundaries: 239.0.1/24: : 239.1.2/24
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 sub
nets 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 incom
ing 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 desti
nation group on that leaf.
The mrouted utility also maintains a copy of the kernel for
warding 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 For; wvifs
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 (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 up
stream, 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 data
grams 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 sub
net. 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 inter
face.
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.

AUTHORS

Steve Deering,
Ajit Thyagarajan,
Bill Fenner.
BSD May 8, 1995

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See also