mrouted(1M)mrouted(1M)NAMEmrouted - IP multicast routing daemon
SYNOPSIS
config_file] debug_level]
DESCRIPTION
The command is an implementation of the Distance-Vector Multicast Rout‐
ing 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 Multicast‐
ing.
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, includes support
for "tunnels", which are virtual point-to-point links between pairs of
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. By
default, the packets are encapsulated using the IP-in-IP protocol (IP
protocol number 4).
The tunnelling mechanism allows 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.
handles multicast routing only; there may or may not be unicast routing
software running on the same machine as With the use of tunnels, it is
not necessary for to have access to more than one physical subnet in
order to perform multicast forwarding.
Invocation
If the option is not specified or if the debug level is specified as 0,
detaches from the invoking terminal. Otherwise, it remains attached to
the invoking terminal and responsive to signals from that terminal. If
is specified with no argument, the debug level defaults to 2. Regard‐
less of the debug level, always writes warning and error messages to
the system log demon. Nonzero debug levels have the following effects:
level 1 all messages are also printed to
level 2 all level 1 messages plus notifications of "significant"
events are printed to
level 3 all level 2 messages plus notifications of all packet
arrivals and departures are printed to
Upon startup, writes its pid to the file
Configuration
automatically configures itself to forward on all multicast-capable
interfaces (i.e., interfaces that have the IFF_MULTICAST flag set,
excluding the loopback "interface"). finds other directly reachable
via those interfaces. To override the default configuration or to add
tunnel links to other configuration commands may be placed in (or an
alternative file, specified by the option). There are four types of
configuration commands:
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; white space (including newlines) is not
significant. The boundary and altnet options may be specified as many
times as necessary.
The command can be used to disable multicast routing on the physical
interface identified by local IP address <local-addr>, or to associate
a nondefault metric or threshold with the specified physical interface.
The local IP address <local-addr> may be replaced by the interface name
(such as ). If is attached to multiple IP subnets, describe each addi‐
tional subnet with the altnet option. commands must precede commands.
The command can be used to establish a tunnel link between local IP
address <local-addr> and remote IP address <remote-addr>, and to asso‐
ciate a nondefault metric or threshold with that tunnel. The local IP
address <local-addr> may be replaced by the interface name (such as 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 files of both routers before it can be
used.
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 command is provided for to act as a nonpruning router. It is also
possible to start in a nonpruning mode using the 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 command. The boundary option on or commands can accept either a
name or a boundary.
The metric option 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. Metrics should be kept as small
as possible because 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.
In general, all connected to a particular subnet or tunnel should use
the same metric and threshold for that subnet or tunnel.
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 0 (unlimited) on physi‐
cal interfaces.
The boundary option allows an interface to be configured as an adminis‐
trative 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.
will not initiate execution if it has fewer than two enabled vifs (vir‐
tual interface), where a vif is either a physical multicast-capable
interface or a tunnel. It will log a warning if all of its vifs are
tunnels; such an configuration would be better replaced by more direct
tunnels.
Example Configuration
This is an example configuration for a multicast router at a large
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
#
# lan1 is our gateway to compsci, don't forward our
# local groups to them
phyint lan1 boundary EE
#
# lan2 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
responds to the following signals:
HUP restarts 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).
TERM same as INT
USR1 dumps the internal routing tables to
USR2 dumps the internal cache tables to
QUIT dumps the internal routing tables to (only if was invoked
with a nonzero debug level).
For convenience in sending signals, writes its pid to upon startup.
EXAMPLES
The routing tables look like this:
Virtual Interface Table
Vif Local-Address Metric Thresh Flags
0 36.2.0.8 subnet: 36.2 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 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 (2.2)
boundaries: 239.0.1
: 239.1.2
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 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 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 number of incoming and
outgoing packets is also shown at each interface.
Associated with each subnet from which a multicast datagram can origi‐
nate 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 an update was received for this subnet, the incom‐
ing vif for multicasts from that origin, and a list of outgoing vifs.
The asterisk ( ) indicates 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 command also maintains a copy of the kernel forwarding cache table.
Entries are created and deleted by
The cache tables look like this:
Multicast Routing Cache Table (147 entries)
Origin Mcast-group CTmr Age Ptmr IVif Forwvifs
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, 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 sim‐
ply 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 incom‐
ing vif for multicast packets from that origin. Each router also main‐
tains 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 sub‐
net, a prune message is sent to the upstream router. They are indi‐
cated by a after the vif number. The Forwvifs field shows the inter‐
faces along which datagrams belonging to the source-group are for‐
warded. A 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 on an interface indicates that
it is a boundary interface; that is, 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.
AUTHOR
was developed by Steve Deering, Ajit Thyagarajan, Bill Fenner.
FILESSEE ALSOmap-mbone(1M), mrinfo(1M).
DVMRP is described, along with other multicast routing algorithms, in
the paper "Multicast Routing in Internetworks and Extended LANs" by S.
Deering, in the
mrouted(1M)