path: root/usr.sbin/mrouted/mrouted.8

'\"COPYRIGHT 1989 by The Board of Trustees of Leland Stanford Junior University.
.TH MROUTED 8
.UC 5
.SH NAME
mrouted \- IP multicast routing daemon
.SH SYNOPSIS
.B /etc/mrouted 
[
.B \-p
] [
.B \-c 
.I config_file
] [
.B \-d 
[ 
.I debug_level
]]
.SH DESCRIPTION
.I 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
.I 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, 
.I mrouted 
includes support for
"tunnels", which are virtual point-to-point links between pairs of 
.IR mrouted 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 
.I mrouted
tunnel using IP source routing, which puts a heavy load on some
types of routers.
This version supports IP source route tunnelling only for backwards 
compatibility.
.PP
The tunnelling mechanism allows 
.I 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.
.I Mrouted 
suffers from the well-known scaling problems of any distance-vector
routing protocol, and does not (yet) support hierarchical multicast routing.
.PP
.I Mrouted 
handles multicast routing only; there may or may not be unicast routing
software running on the same machine as 
.IR mrouted .
With the use of tunnels, it
is not necessary for 
.I mrouted 
to have access to more than one physical subnet
in order to perform multicast forwarding.
.br
.ne 5
.SH INVOCATION
.PP
If no "\-d" option is given, or if the debug level is specified as 0, 
.I mrouted
detaches from the invoking terminal.  Otherwise, it 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, 
.I mrouted 
always writes warning and error messages to the system
log demon.  Non-zero debug levels have the following effects:
.IP "level 1"
all syslog'ed messages are also printed to stderr.
.IP "level 2"
all level 1 messages plus notifications of "significant"
events are printed to stderr.
.IP "level 3"
all level 2 messages plus notifications of all packet
arrivals and departures are printed to stderr.
.SH CONFIGURATION
.PP
.I 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
.IR mrouted s
directly reachable
via those interfaces.  To override the default configuration, or to add
tunnel links to other
.IR mrouted s,
configuration commands may be placed in
/etc/mrouted.conf (or an alternative file, specified by the "\-c" option).
There are four types of configuration commands:
.nf

    phyint <local-addr>   [disable]   [metric <m>]
		 [threshold <t>] [rate_limit <b>]
		   [boundary <scoped-addr>/<mask-len>]

    tunnel <local-addr> <remote-addr> [metric <m>]
		 [threshold <t>] [srcrt] [rate_limit <b>]
		   [boundary <scoped-addr>/<mask-len>]

    cache_lifetime <ct>

    pruning <off/on>

.fi
.PP
One note about the configuration commands - all the phyint and tunnel 
command options must be on a single line except for the boundary option
which may begin on a separate line. A single phyint or tunnel command may
have multiple boundary options.
.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 alternatively replaced by the 
interface name (e.g le0) for the phyint command only.
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 tunnel must be set
up in the mrouted.conf files of both routers before it can be used.
For backwards compatibility with older
.IR mrouted s,
the srcrt keyword specifies 
encapsulation using IP source routing.
.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
The pruning <off/on> option is provided for
.IR mrouted
to act as a non-pruning router. It is also possible to start 
.Ir 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.
.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 
.I mrouted
cannot route along paths with a sum of metrics greater
than 31.
.LP
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.
.LP
In general, all
.IR mrouted 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.
.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.
.PP
.I 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 
.I mrouted
configuration would be better replaced by more
direct tunnels (i.e., eliminate the middle man).
.SH SIGNALS
.PP
.I Mrouted 
responds to the following signals:
.IP HUP
restarts
.I mrouted .
The configuration file is reread every time this signal is evoked.
.IP INT
terminates execution gracefully (i.e., by sending
good-bye messages to all neighboring routers).
.IP TERM
same as INT
.IP USR1
dumps the internal routing tables to /usr/tmp/mrouted.dump.
.IP USR2
dumps the internal cache tables to /usr/tmp/mrouted.cache.
.IP QUIT
dumps the internal routing tables to stderr (only if
.I mrouted 
was invoked with a non-zero debug level). 
.bp
.SH EXAMPLE
.PP
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  In-Vif  Out-Vifs
 36.2                               1       0    1* 2  3*
 36.8            36.8.0.77          4       2    0* 1* 3*
 36.11                              1       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 
.I 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.
.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 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.
.bp
.PP
.I Mrouted 
also maintains a copy of the kernel forwarding cache table. Entries
are created and deleted by 
.I mrouted.
.PP
The cache tables look like this:
.nf

Multicast Routing Cache Table (325 entries)
 Origin-Subnet   Mcast-group    CTmr IVif Prcv# Psnt Forwvifs
 134.207.7       224.2.140.239   300   1    0        0  2 
 138.15.103      224.2.203.214   295   1    2    P   0p 2p
 128.237.0       224.2.253.119   290   1    1        0  2p
 129.215.200     224.2.207.48     40   1    1        0p 2 
 36.77.14        239.0.1.234     345   2b

.fi 
Each entry is characterized by the origin subnet number and the
destination multicast group. The 'CTmr' field indicates the lifetime
(in seconds) of the entry.  The entry is deleted from the cache table
when the timer decrements to zero. 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 neighbouring
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" in the Psnt field.  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.


.SH FILES
/etc/mrouted.conf
.SH SEE ALSO
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
Steve Deering & Ajit Thyagarajan