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freebsd-src/usr.sbin/mrouted/mrouted.8

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.\"COPYRIGHT 1989 by The Board of Trustees of Leland Stanford Junior University.
.\"$Id: mrouted.8,v 1.9 1997/02/22 16:06:59 peter Exp $
.Dd May 8, 1995
.Dt MROUTED 8
.UC 5
.Sh NAME
.Nm mrouted
.Nd IP multicast routing daemon
.Sh SYNOPSIS
.Nm mrouted
.Op Fl c Ar config_file
.Op Fl d Op Ar debug_level
.Op Fl p
.Sh DESCRIPTION
.Nm 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.
.Pp
.Nm 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.
.Pp
In order to support multicasting among subnets that are separated by (unicast)
routers that do not support IP multicasting,
.Nm
includes support for
"tunnels", which are virtual point-to-point links between pairs of
.Nm mrouted Ns s
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
.Nm
tunnel using IP source routing, which puts a heavy load on some
types of routers.
This version does not support IP source route tunnelling.
.Pp
The tunnelling mechanism allows
.Nm
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.
.Nm Mrouted
suffers from the well-known scaling problems of any distance-vector
routing protocol, and does not (yet) support hierarchical multicast routing.
.Pp
.Nm Mrouted
handles multicast routing only; there may or may not be unicast routing
software running on the same machine as
.Nm mrouted .
With the use of tunnels, it
is not necessary for
.Nm
to have access to more than one physical subnet
in order to perform multicast forwarding.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl c Ar config_file
Specify an alternative file for configuration commands. Default is
.Pa /etc/mrouted.conf .
.It Fl d Op Ar debug_level
If no
.Fl d
option is given, or if the debug level is specified as 0,
.Nm
detaches from the invoking terminal. Otherwise, it remains attached to the
invoking terminal and responsive to signals from that terminal.
If
.Fl d
is given with no argument, the debug level defaults to 2. Regardless of the
debug level,
.Nm
always writes warning and error messages to the system
log demon. Non-zero debug levels have the following effects:
.Bl -tag -width indent
.It "level 1"
all syslog'ed messages are also printed to stderr.
.It "level 2"
all level 1 messages plus notifications of "significant"
events are printed to stderr.
.It "level 3"
all level 2 messages plus notifications of all packet
arrivals and departures are printed to stderr.
.El
.It Fl p
Disable pruning.
.El
.Pp
Upon startup,
.Nm
writes its pid to the file
.Pa /var/run/mrouted.pid .
.Sh CONFIGURATION
.Nm 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
.Nm mrouted Ns s
directly reachable
via those interfaces. To override the default configuration, or to add
tunnel links to other
.Nm mrouted Ns s,
configuration commands may be placed in
.Pa /etc/mrouted.conf
(or an alternative file, specified by the
.Fl c
option).
There are four types of configuration commands:
.nf
phyint <local-addr> [disable] [metric <m>] [advert_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>] [advert_metric <m>]
[threshold <t>] [rate_limit <b>]
[boundary (<boundary-name>|<scoped-addr>/<mask-len>)]
cache_lifetime <ct>
name <boundary-name> <scoped-addr>/<mask-len>
.fi
.Pp
The file format is free-form; whitespace (including newlines) is not
significant.
The
.Em boundary
and
.Em altnet
options may be specified as many times as necessary.
.Pp
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.
.Pp
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
.Pa mrouted.conf
files of both routers before it can be used.
.Pp
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.
.Pp
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.
.Pp
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. Metrics should be kept as small as possible,
because
.Nm
cannot route along paths with a sum of metrics greater
than 31.
.Pp
The advert_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 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.
.Pp
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.
.Pp
In general, all
.Nm mrouted Ns s
connected to a particular subnet or tunnel should
use the same metric and threshold for that subnet or tunnel.
.Pp
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 physical
interfaces.
.Pp
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.
.Pp
.Nm 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
.Nm
configuration would be better replaced by more
direct tunnels (i.e., eliminate the middle man).
.Sh "EXAMPLE CONFIGURATION"
This is an example configuration for a mythical multicast router at a big
school.
.sp
.nf
#
# 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
.fi
.Sh SIGNALS
.Nm Mrouted
responds to the following signals:
.Bl -tag -width indent
.It HUP
Restarts
.Nm mrouted .
The configuration file is reread every time this signal is evoked.
.It INT
Terminate execution gracefully (i.e., by sending
good-bye messages to all neighboring routers).
.It TERM
Same as INT.
.It USR1
Dump the internal routing tables to
.Pa /var/tmp/mrouted.dump .
.It USR2
Dump the internal cache tables to
.Pa /var/tmp/mrouted.cache .
.It QUIT
Dump the internal routing tables to stderr (only if
.Nm
was invoked with a non-zero debug level).
.El
.Pp
For convenience in sending signals,
.Nm
writes its pid to
.Pa /var/run/mrouted.pid
upon startup.
.Sh EXAMPLE
The routing tables look like this:
.nf
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*
.
.
.
.fi
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
.Nm
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.
.Pp
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.
.Pp
.Nm Mrouted
also maintains a copy of the kernel forwarding cache table. Entries
are created and deleted by
.Nm mrouted .
.Pp
The cache tables look like this:
.nf
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
.fi
Each entry is characterized by the origin subnet number and mask and the
destination multicast group.
.Pp
The 'CTmr' field indicates the lifetime
of the entry. The entry is deleted from the cache table
when the timer decrements to zero.
.Pp
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.
.Pp
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.
.Pp
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.
.Pp
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.
.Pp
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.
.Sh FILES
.Bl -tag -width /var/tmp/mrouted.cache -compact
.It Pa /etc/mrouted.conf
.It Pa /var/run/mrouted.pid
.It Pa /var/tmp/mrouted.dump
.It Pa /var/tmp/mrouted.cache
.El
.Sh SEE ALSO
.Xr mrinfo 8 ,
.Xr mtrace 8 ,
.Xr map-mbone 8
.Pp
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.
.Sh AUTHORS
.An Steve Deering ,
.An Ajit Thyagarajan ,
.An Bill Fenner .
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