MROUTED.CONF(5) File Formats Manual MROUTED.CONF(5)


mrouted.confmrouted configuration file




In many cases you do not need to configure mrouted. It configures itself automatically to forward multicast on all multicast-capable interfaces, i.e., interfaces that have the IFF_MULTICAST flag set, excluding the loopback interface. It locates other DVMRP capable routers directly reachable via those interfaces.
will not start with less than two enabled virtual interfaces (VIFs). A VIF is either a physical multicast-capable interface or a tunnel.
will log a warning if all of its VIFs are tunnels; such a configuration is likely better replaced by more direct (GRE) tunnels (i.e. eliminate the middle man).
To override the default settings, for example to add tunnel links to other DVMRP routers, configuration commands may be placed in /etc/mrouted.conf. The file format is free-form: whitespace (including newlines) is not significant. The “#” character marks start of a comment to end of line.
cache-lifetime <60-86400>
This setting defines the time in seconds 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.
prune-lifetime <120-86400>
The average lifetime in seconds of prunes sent towards parents. The actual lifetimes are randomized in the range [.5secs, 1.5secs]. Smaller values cause less state to be kept both at this router and the parent, at the cost of more frequent broadcasts. However, some routers (e.g. mrouted <3.3 and all currently known versions of Cisco's IOS) do not use the DVMRP generation ID to determine that a neighbor has rebooted. Prunes sent towards these neighbors should be kept short, in order to shorten the time to recover from a reboot. For use in this situation, the prune-lifetime keyword may be specified on an interface as described below. It defaults to 7200.
name boundary-name scoped-addr/mask-len
The name option assigns names to boundaries to make configuration per interface/tunnel easier.
mrouted uses a DVMRP optimization to prevent having to keep individual routing tables for each neighbor; part of this optimization is that mrouted assumes that it is the forwarder for each of its attached subnets on startup. This can cause duplicates for a short period (approximately one full route report interval), since both the router that just started up and the proper forwarder will be forwarding traffic. This behavior can be turned off with the noflood keyword; mrouted will not assume that it is the forwarder on startup. Turning on noflood can cause black holes on restart, which generally lasts approximately one full route report interval.
The noflood keyword can also be specified on individual interfaces.
rexmit-prunes [on | off]
The default is to retransmit prunes on all point-to-point interfaces (including tunnels) but no multi-access interfaces. This option may be used to make the default on (or off) for all interfaces.
The rexmit-prunes keyword can also be specified on individual interfaces.
no router-alert
Some multicast routers, and some IGMP snooping switches, do not support IP options like Router Alert, which is enabled in mrouted by default. This command to disable this IP option. Regardless of this setting, mrouted always calculates the IP payload offset based on the IP header length value of ingressing DVMRP and IGMP frames.
igmp-query-interval <1-1024>
This setting controls the IGMP query interval in seconds, used when this router is elected querier on a LAN. It is not recommended to go below 10 sec. Default: 125.
igmp-robustness <2-10>
This setting controls many aspects of IGMP timers, for end devices and routers alike. The query-response-interval used below is hard-coded to 10 sec in mrouted:
Group Membership Timeout
Number of seconds before mrouted determines that there are no more members of a group on a LAN. Formula: (igmp-robustness x igmp-query-interval) + (1 x query-response-interval)
Other Querier Timeout
Number of seconds before mrouted determines there is no longer an elected querier on the LAN. Formula: (igmp-robustness x igmp-query-interval) + (0.5 x query-response-interval)
Last-member Query Count
Number of group-specific queries sent before mrouted assumes there are no local members of a group. The number of queries is equal to the value of the robustness variable. However, mrouted currently hard-codes this to 2
no phyint
By default all interfaces are enabled. This command disables all interfaces, useful on routers with lots of interfaces where mrouted should run on only only a select few.
no phyint 
phyint eth10 enable 
phyint eth12 enable
Note: Most UNIX kernels, including Linux, have a hard coded limit of 32 VIFs. In non-trivial setups this limit is often reached, causing weird errors that can be hard to debug. The recommendation for those cases is to disable all phyint (this setting), and then selectively enable only the ones needed.
phyint <local-addr | ifname> [disable | enable] [passive] [blaster] [force-leaf] [noflood] [igmpv1 | igmpv2 | igmpv3] [altnet network/mask-len] [boundary boundary-name | scoped-addr/mask-len] [metric <1-31>] [advert-metric <0-31>] [prune-lifetime sec] [rexmit-prunes [on | off]] [allow-nonpruners] [notransit] [accept|deny (route/mask-len [exact])+ [bidir]] [rate-limit kbps] [threshold ttl]
This setting selects and alters properties of the phyiscal interfaces mrouted operates on. Interfaces can be identified using their local IP address or their name.
NOTE: All phyint commands must precede tunnel commands.
disable | enable
Selectively disable or enable this interface. Only enabled interfaces get a VIF in the kernel.
beside [on | off]
This is a tunnel option. For compatibility with older mrouted routers the default is to unicast control traffic "beside" the tunnel. To encapsulate all control traffic inside the tunnel use beside off.
igmpv1 | igmpv2 | igmpv3
mrouted supports all IGMP versions. Use these flags to force compatibility modes on the given interface. Default: igmpv3
altnet network/mask-len
If an interface is attached to multiple IP subnets, describe each additional subnet with this keyword.
boundary boundary-name | scoped-addr/mask-len
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.
metric <1-31>
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 "cost" advertised to neighbors for the given interface or tunnel; it may be used to influence the choice of routes on the neighbor side. 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.
Force mrouted to ignore other routers on this interface. mrouted will never send or accept neighbor probes or route reports on this interface.
As described above, but only applicable to this interface/tunnel.
No packets will be sent on this link or tunnel until we hear from the other end. This is useful for the "server" end of a tunnel that goes over a dial-on-demand link; configure the "server" end as passive and it will not send its periodic probes until it hears one from the other side, so will not keep the link up. If this option is specified on both ends of a tunnel, the tunnel will never come up.
Enable handling of routers (mostly Cisco) that overwhelm socket buffers by "blasting" the whole routing table at once.
prune-lifetime sec
As described above, but only applicable to this interface/tunnel.
rexmit-prunes [on | off]
As described above, but only applicable to this interface/tunnel. Recall that prune retransmission defaults to on on point-to-point links and tunnels, and off on multi-access links.
By default, mrouted refuses to peer with DVMRP neighbors that do not claim to support pruning. This option allows such peerings on this interface.
A specialized case of route filtering; no route learned from an interface marked notransit will be advertised on another interface marked notransit. Marking only a single interface notransit has no meaning.
accept|deny (route/mask-len [exact])+ [bidir]
The accept and deny commands allow rudimentary route filtering. The accept command causes mrouted to accept only the listed routes on the configured interface; the deny command causes mrouted to accept all but the listed routes. Only one of accept or deny commands may be used on a given interface.
The list of routes follows the accept or deny keyword. If the keyword exact follows a route, then only that route is matched; otherwise, that route and any more specific route is matched. For example, deny 0/0 denys all routes, while deny 0/0 exact denys only the default route. The default route may also be specified with the default keyword.
The bidir keyword enables bidirectional route filtering; the filter will be applied to routes on both output and input. Without the bidir keyword, accept and deny filters are only applied on input. Poison reverse routes are never filtered out.
rate-limit kbps
allows the network administrator to specify a certain bandwidth in kbps which would be allocated to multicast traffic. It defaults to 500 kbps on tunnels, and 0 (unlimited) on physical interfaces.
threshold ttl
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 for multicast is 1.
tunnel local-addr remote-addr [beside [on | off]] [boundary boundary-name | scoped-addr/mask-len] [metric <1-31>] [advert-metric <0-31>] [noflood] [passive] [blaster] [prune-lifetime sec] [rexmit-prunes [on | off]] [allow-nonpruners] [rate-limit kbps] [threshold ttl]
This setting 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.
See the phyint command for details on the relevant tunnel options.
The boundary option to all commands can accept either a name or a network boundary; the boundary and altnet options may be specified as many times as necessary.
In general, all DVMRP routers connected to a particular subnet or tunnel should use the same metric and threshold for that subnet or tunnel.


This is an example configuration for a mythical multicast router at a big school.
# 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 
# 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. 
       metric 1 threshold 1 rate-limit 0 
# This is our tunnel to the outside world. 
# Careful with those boundaries, Eugene. 
       metric 1 threshold 32 
       boundary LOCAL boundary EE


Main configuration file.


mrouted(8), mroutectl(8)


This manual page was written by Joachim Wiberg ⟨⟩.
June 9, 2020 Debian