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AIX Version 4.3 Commands Reference, Volume 3

mrouted Daemon


Forwards a multicast datagram. This daemon only applies to AIX Version 4.2.1 or later.


/usr/sbin/mrouted [ -p ] [ -c Config_File ] [ -d [ Debug_Level ] ]


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 using a distance vector routing protocol (like RIP, described in RFC 1058), on 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 that 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.

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 mrouteds 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 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 support hierarchical multicast routing.

mrouted automatically configures itself to forward on all multicast-capable interfaces (that is, interfaces that have the IFF_MULTICAST flag set, excluding the loopback interface), and it finds other mrouteds directly reachable using those interfaces.

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.

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 to perform multicast forwarding.


-c Config_File Starts the mrouted command using an alternate configuration file specified by the Config_File variable.

There are five types of configuration entries:

phyint local-addr [disable] [metric m] [threshold t] [rate_limit b]
[boundary (boundary-name|scoped-addr/mask-len)] [altnet
tunnel local-addr remote-addr
metric m
] [
threshold t
] [
rate_limit b



cache_lifetime ct
pruning off
name boundary-name scoped-addr

See mrouted.conf File in AIX Version 4.3 Files Reference.

-d Sets the debug level. 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 demon. Non-zero debug levels have the following effects:
level 1 All syslog'ed messages are also printed to stderr.
level 2 All level 1 messages plus notifications of significant events are printed to stderr.
level 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 /etc/mrouted.pid.

-p Turns off pruning. Default is pruning enabled.


The following signals can be sent to mrouted:

HUP Restarts mrouted. The configuration file is reread every time this signal is evoked.
INT Terminates execution gracefully (that is, by sending good-bye messages to all neighboring routers).
TERM Same as INT.
USR1 Dumps the internal routing tables to /usr/tmp/mrouted.dump.
USR2 Dumps the internal cache tables to /usr/tmp/mrouted.cache.
QUIT Dumps the internal routing tables to stderr (if mrouted was invoked with a nonzero debug level).

For convenience in sending signals, mrouted writes its pid to /etc/mrouted.pid on startup.


  1. To display routing table information, enter:
    kill -USR1 *cat /etc/mrouted.pid*
    This produces the following output:
    Virtual Interface Table
     Vif Local-Address                    Metric   Thresh   Flags 
      0     subnet: 36.2           1        1     querier  
                     pkts in: 3456 
                    pkts out: 2322323
      1    subnet: 36.11          1        1     querier
                     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 directly connected), the metric of the path back to the origin, the amount of time since an update for this subnet was last received, the incoming vif for multicasts from that origin, and a list of outgoing vifs. The asterisk (*) 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.

  2. To display cache table information, enter:
    kill -USR2 *cat /etc/mrouted.pid*
    This produces the following output:
    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 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 are no members of the particular group on that subnet. A b 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 greater-than symbol (>) as the first character is printed for each source on the subnet. Note that there can be many sources in one subnet.


/etc/mrouted.conf Contains the configuration information for the mrouted daemon.
/usr/tmp/mrouted.dump Contains the internal routing tables for the mrouted daemon.
/etc/mrouted.pid Contains the process ID for the mrouted daemon.
/usr/tmp/mrouted.cache Contains the internal cache tables for the mrouted daemon.

Related Information

/etc/mrouted.conf File in AIX Version 4.3 Files Reference.

DVMRP is described, along with other multicast routing algorithms, in the paper "Multicast Routing in Internetworks and Extended LANs" by S. Deering in Proceedings of the ACM SIGCOMM '88 Conference.

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