MROUTED(8) OpenBSD System Manager's Manual MROUTED(8)NAMEmrouted - IP multicast routing daemon
SYNOPSISmrouted [-p] [-c config_file] [-d [debug_level]]
DESCRIPTIONmrouted 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 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 mrouted daemons 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). Older versions of mrouted tunnel use
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. mrouted suffers from the well-known scaling problems
of any distance-vector routing protocol, and does not (yet) support
hierarchical 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 options are as follows:
-c config_file
Specify an alternative configuration file, instead of the default
mrouted.conf.
-d [debug_level]
By default, mrouted detaches from the invoking terminal. If this
option is specified, mrouted remains attached to the invoking
terminal and responsive to signals from that 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 daemon. Debug levels have the
following effects:
0 Detach from the invoking terminal.
1 All syslog(3) messages are also printed to stderr.
2 All level 1 messages plus notifications of
"significant" events are printed to stderr.
3 All level 2 messages plus notifications of all
packet arrivals and departures are printed to
stderr.
-p Start mrouted in a non-pruning mode. It is expected that a
router would be configured in this manner for test purposes only.
The default mode is pruning enabled.
mrouted 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 mrouted directly
reachable via those interfaces. To override the default configuration,
or to add tunnel links to other mrouted, configuration commands may be
placed in /etc/mrouted.conf. There are five types of configuration
commands:
cache_lifetime ct
name boundary-name | scoped-addr/mask-len
phyint local-addr [altnet network/mask-len]
[boundary boundary-name | scoped-addr/mask-len] [disable]
[metric m] [rate_limit b] [threshold t]
pruning [off | on]
tunnel local-addr remote-addr
[boundary boundary-name | scoped-addr/mask-len] [metric m]
[rate_limit b] [threshold t]
The file format is free-form: whitespace (including newlines) is not
significant. The boundary option can accept either a name or a boundary;
the boundary and altnet options may be specified as many times as
necessary.
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 name option assigns names to boundaries to make configuration easier.
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 replaced by the
interface name (e.g. le0). If a phyint is attached to multiple IP
subnets, describe each additional subnet with the altnet keyword. Phyint
commands must precede tunnel commands.
The pruning option is provided for mrouted to act as a non-pruning
router.
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. le0). 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.
boundary 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.
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. Metrics should be kept as small as possible,
because mrouted cannot route along paths with a sum of metrics greater
than 31.
rate_limit 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 physical
interfaces.
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 mrouted connected to a particular subnet or tunnel should
use the same metric and threshold for that subnet or tunnel.
mrouted will not initiate execution if it has fewer than two enabled
virtual interfaces (vifs), 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 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
SIGNALSmrouted 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).
TERM The same as INT.
USR1 Dumps the internal routing tables to /var/tmp/mrouted.dump.
USR2 Dumps the internal cache tables to /var/tmp/mrouted.cache.
QUIT Dumps 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 process ID to
/var/run/mrouted.pid upon startup.
FILES
/etc/mrouted.conf
/var/tmp/mrouted.cache
/var/tmp/mrouted.dump
/var/run/mrouted.pid
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 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 number 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
13.2.116/22 224.2.127.255 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 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.
SEE ALSOmap-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
Steve Deering, Ajit Thyagarajan, Bill Fenner
OpenBSD 4.9 April 5, 2010 OpenBSD 4.9
