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NAME    [Toc]    [Back]

     mrouted - IP multicast routing daemon

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     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.

     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
     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-inIP
 protocol (IP  protocol  number  4).   Older  versions  of
mrouted tunnel use
     IP  source routing, which puts a heavy load on some types of
     This version does not support IP source route tunneling.

     The tunneling 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.

INVOCATION    [Toc]    [Back]

     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  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.  Non-zero debug levels
have the following

           1       All syslog'ed messages  are  also  printed  to
           2        All  level  1  messages plus notifications of
                   events are printed to stderr.
           3       All level 2 messages plus notifications of all
packet arrivals
 and departures are printed to stderr.

     Upon   startup,   mrouted   writes   its  pid  to  the  file

CONFIGURATION    [Toc]    [Back]

     mrouted automatically configures itself to  forward  on  all
 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
     or to add tunnel links to other mrouted, configuration  commands may be
     placed  in /etc/mrouted.conf (or an alternative file, specified by the -c
     option).  There are five types of configuration commands:

           phyint <local-addr> [disable] [metric <m>]
                 [threshold <t>] [rate_limit <b>]
                 [boundary  (<boundary-name>|<scoped-addr>/<masklen>)]
                 [altnet <network>/<mask-len>]

           tunnel <local-addr> <remote-addr> [metric <m>]
                 [threshold <t>] [rate_limit <b>]
                 [boundary  (<boundary-name>|<scoped-addr>/<masklen>)]

           cache_lifetime <ct>

           pruning <off/on>

           name <boundary-name> <scoped-addr>/<mask-len>

     The file format is  free-form;  whitespace  (including  newlines) is not significant.
   The boundary and altnet options may be specified
as many times
     as necessary.

     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 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.

     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 pruning option is provided for mrouted to act as a  nonpruning
     router.  It is also possible to start 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.

     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.

     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  mrouted cannot route along paths with a sum of metrics greater
     than 31.

     The threshold is the minimum IP time-to-live required for  a
     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
     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.

     The  rate_limit  option  allows the network administrator to
specify a certain
 bandwidth in Kbits/second which would be  allocated  to
     traffic.  It defaults to 500Kbps on tunnels, and 0 (unlimited) on physical

     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.

     mrouted will not initiate execution if it has fewer than two
     vifs, where a vif (virtual interface) is either  a  physical
  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).


     This  is  an  example configuration for a mythical multicast
router at a big
     # mrouted.conf example
     # Name our boundaries to make it easier.
     name LOCAL
     name EE
     # 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 boundary EE altnet
          altnet altnet
     # 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 metric 1 threshold 1
          rate_limit 0
     # This is our tunnel to the outside world.
     # Careful with those boundaries, Eugene.
     tunnel metric 1 threshold 32
          boundary LOCAL boundary EE

SIGNALS    [Toc]    [Back]

     mrouted 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  same as INT
     USR1     dumps    the    internal    routing    tables    to
     USR2      dumps     the    internal    cache    tables    to
     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 pid
     /var/run/mrouted.pid upon startup.

FILES    [Toc]    [Back]


EXAMPLES    [Toc]    [Back]

     The routing tables look like this:

     Virtual Interface Table
      Vif  Local-Address                    Metric  Thresh  Flags
       0        subnet:   36.2            1        1
                        pkts in: 3456
                       pkts out: 2322323

       1       subnet:   36.11           1         1
                        pkts in: 345
                       pkts out: 3456

       2      tunnel:     3       1
                          peers: (2.2)
                     boundaries: 239.0.1
                               : 239.1.2
                        pkts in: 34545433
                       pkts out: 234342

       3     tunnel:      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            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 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 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     3m   2m    -  0    1
      138.96.48/21     5m   2m    -  0    1
      128.9.160/20     3m   2m    -  0    1
      198.106.194/24     9m  28s   9m  0P

     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
     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 ALSO    [Toc]    [Back]

     map-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    [Toc]    [Back]

     Steve Deering, Ajit Thyagarajan, Bill Fenner

OpenBSD      3.6                            May      8,      1995
[ Back ]
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