MROUTED(8) (smm)
MROUTED(8) System Manager's Manual (smm) MROUTED(8)

NAME

mroutedIP multicast routing daemon

SYNOPSIS

mrouted [-hnsv] [-d SYS[,SYS,...] [-f FILE] [-l LEVEL] [-w SEC]

DESCRIPTION

mrouted is the original implementation of the Distance-Vector Multicast Routing Protocol (DVMRP), RFC 1075. A dynamic (automatic) multicast routing daemon.
mrouted is simple to use. DVMRP is derived from RIP, RFC 1058, which means mrouted works stand-alone without any extra network setup required. You can get up and running in a matter of minutes.
mrouted maintains topological knowledge via DVMRP, upon which it implements a multicast datagram forwarding algorithm called Reverse Path Multicasting.
mrouted forwards multicast datagrams along the 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, you can set up GRE tunnels. However, mrouted includes (built-in) support for IP-in-IP tunnels, which are virtual point-to-point links between pairs of DVMRP capable rotuers 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.
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.
A more common practise today is to set up GRE tunnels between multicast capable routers and limit mrouted to run on a select number of interfaces listed in the configuration.
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.

OPTIONS

This program follows the usual UNIX command line syntax, with long options starting with two dashes (`--'). The options are as follows:
-d, --debug SYS[,SYS,..]
This option enables subsystem debug messages and causes mrouted to run in the foreground of the starting terminal, regardless of the -l flag controls the (syslog) log level of each subsystem. Use '?' for a complete list of supported subsystems.
Available subystems:
packet
Display the type, source and destination of all packets sent or received
pruning
Display more information about prunes sent or received
routing
Display more information about routing update packets sent or received
route-detail
Display routing updates in excruciating detail. This is generally way too much information
neighbors
Display information about neighbor discovery
cache
Display insertions, deletions and refreshes of entries in the kernel forwarding cache
timer
Debug timeouts and periodic processes
interface
Display information about interfaces and their configuration
membership
Display information about group memberships on physical interfaces
traceroute
Display information about multicast traceroute requests passing through this router
igmp
Display IGMP operation including group membership and querier election
icmp
Monitor ICMP handling
rsrr
Monitor RSRR operation
all
Enable all debug messages (except noisy timer)
-f, --config FILE
Specify an alternative configuration file, default /etc/mrouted.conf
-h, --help
Print a help message and exit.
-l, --loglevel LEVEL
Set log level for syslog messages: none, err, notice (default), info, debug. Use '?' for a complete list of supported log levels.
none
Disable all logging
error
Error conditions
warning
Warning conditions
notice
Normal but significant condition (default)
info
Informational
debug
Debug-level messages
-n, --foreground
Run in foreground, do not detach from controlling terminal. This option is usually required when running under process supervisors like systemd and Finit, but is also useful when running from the terminal, when debugging a config or at initial set up. Remember to also give the -s option if you still want to redirect log messages to the syslog.
-w, --startup-delay SEC
Wait for SEC seconds before applying routes. This delay allows exchange of routes before starting to forward multicast packets. In certain setups this can prevent transient problems at startup, at the cost of a momentary black hole.
-s, --syslog
Use syslog(3) for log messages, warnings and error conditions. This is the default when running in the background. When running in the foreground, see -n, log messages are printed to stdout.

SIGNALS

mrouted responds to the following signals:
HUP
Restart mrouted and reload the configuration file.
INT
Terminate execution gracefully, i.e., by sending good-bye messages to all neighboring routers.
TERM
Same as INT.
For convenience, mrouted writes its process ID to /var/run/mrouted.pid when it has completed its start up and is ready to receive signals.

FILES

/etc/mrouted.conf
Main configuration file.
/var/lib/misc/mrouted.genid
DVMRP generation ID. Used by neighboring DVRMP routers to detect when a router is restarted. On BSD /var/db/mrouted.genid is used.
/var/run/mrouted.pid
Pidfile (re)created by mrouted daemon when it has started up and is ready to receive commands.
/var/run/mrouted.sock
UNIX-domain socket used for communication with mroutectl(8)
/proc/net/ip_mr_cache
Holds active IPv4 multicast routes (Linux).
/proc/net/ip_mr_vif
Holds the IPv4 virtual interfaces used by the active multicast routing daemon (Linux).

COMPATIBILITY

Dynamic multicast routing has never been use-case 1a for UNIX systems. Most systems are by default tuned to act as workstations, end devices. When something does not work, or only sort of works, run ‘mrouted -l debug -d all’, optionally also with -n, to get full logs of its interaction with the system.
Particular problems include, but are not limited to:
ENOPROTOOPT
Or similar, with an error message like this:
Cannot enable multicast routing in kernel
    
This comes from missing multicast routing support in the kernel. On Linux you need at least:
CONFIG_IP_MROUTE=y
    
On *BSD:
options    MROUTING         # Multicast routing
    
ENOBUFS
On Linux systems a common problem is that of many interfaces. The error message used to be something like this:
Cannot join group 224.0.0.4: No buffer space available
    
Today that cryptic message has been replaced with a request to adjust /proc/sys/net/ipv4/igmp_max_memberships to a value at least 3x the number of vifs to run on, e.g., by setting it in /etc/sysctl.conf or similar, depending on the system.

SEE ALSO

mrouted.conf(5), mroutectl(8), map-mbone(8), mrinfo(8), mtrace(8), pimd(8), smcroute(8)
S. Deering, Multicast Routing in Internetworks and Extended LANs, Proceedings of the ACM SIGCOMM '88 Conference.
The mrouted home page is ⟨https://github.com/troglobit/mrouted⟩

AUTHORS

The following are the principal authors of mrouted, listed in no particular order:
David Waitzman,
Craig Partridge,
Steve Deering,
Ajit Thyagarajan,
Bill Fenner,
David Thaler,
and
Daniel Zappala.
With contributions by many others.
June 9, 2020 Debian