SMCRoute is a UNIX/Linux tool to manage and monitor multicast routes. It supports both IPv4 and IPv6 multicast routing.
SMCRoute can be used as an alternative to dynamic multicast routers like mrouted or pimd in setups where static multicast routes should be maintained and/or no proper IGMP or MLD signaling exists.
Multicast routes exist in the UNIX kernel as long as a multicast routing
daemon is running. Only one multicast routing daemon can be active at a
time, so it is not possible to run smcrouted and, e.g. mrouted at
the same time.
- Configuration file support,
/etc/smcroute.conf - Support for restarting and reloading the
.confonSIGHUP - Source-less on-demand routing, a.k.a. (*,G) based static routing
- Optional built-in mrdisc support, RFC4286
- Client with built-in support to show routes and joined groups
SMCRoute is both a daemon and a client. To set multicast routes and
join groups you must start the daemon. Use smcrouted -n to run the
daemon in the foreground, as required by systemd and Finit.
By default smcrouted reads /etc/smcroute.conf, which can look
something like this:
mgroup from eth0 group 225.1.2.3
mgroup from eth0 group 225.1.2.3 source 192.168.1.42
mroute from eth0 group 225.1.2.3 source 192.168.1.42 to eth1 eth2
The first line means "Join multicast group 225.1.2.3 on interface eth0".
Useful if eth0 is not directly connected to the source, but to a LAN
with switches with IGMP snooping. Joining the group opens up multicast
for that group towards eth0. Only 20 groups can be joined, for large
setups investigate enabling multicast router ports in the switches, or
possibly use a dynamic multicast routing protocol.
The second mgroup is for source specific group join, i.e. the host
specifies that it wants packets from 192.168.1.42 and no other source.
The third mroute line is the actual layer-3 routing entry. Here we
say that multicast data originating from 192.168.1.42 on eth0 to the
multicast group 225.1.2.3 should be forwarded to interfaces eth1 and
eth2.
Note: To test the above you can use ping from another device. The multicast should be visible as long as your IP# matches the source above and you ping 225.1.2.3 AND REMEMBER TO SET TTL >1!
$ ping -I eth0 -t 2 225.1.2.3
The TTL is what usually bites people trying out multicast routing. Most
TCP/IP stacks default to a TTL of 1 for multicast frames, e.g. ping
requires -t 2, or greater, for multicast. This limitation reduces the
risk of accidentally flooding multicast. Remember, multicast behaves
like broadcast unless limited.
# smcrouted -e /path/to/script
With -e CMD a user script or command can be called when smcrouted
receives a SIGHUP or installs a multicast route to the kernel. This
is useful if you, for instance, also run a NAT firewall and need to
flush connection tracking after installing a multicast route.
# smcrouted -N
With the -N command line option SMCRoute does not prepare all system
interfaces for multicast routing. Very useful if your system has a lot
of interfaces but only a select few are required for multicast routing.
Use the following in /etc/smcroute.conf to enable interfaces:
phyint eth0 enable
phyint eth1 enable
phyint eth2 enable
It is possible to use any interface that supports the MULTICAST flag.
SMCRoute also has a client interface to interact with the daemon:
# smcroutectl join eth0 225.1.2.3
# smcroutectl add eth0 192.168.1.42 225.1.2.3 eth1 eth2
There are more commands. See the man page or the online help for details:
# smcroutectl help
Multicast often originates from different sources but usually never at the same time. For a more generic setup, and to reduce the number of rules required, it is possible to set (*,G) IPv4 multicast routes.
Example smcroute.conf:
mgroup from eth0 group 225.1.2.3
mroute from eth0 group 225.1.2.3 to eth1 eth2
or, from the command line:
# smcroutectl join eth0 225.1.2.3
# smcroutectl add eth0 225.1.2.3 eth1 eth2
Another experimental feature is multicast router discovery, mrdisc,
described in RFC4286. This feature is disabled by default, enable
with configure --enable-mrdisc. When enabled it periodically sends
out an IGMP message on all inbound interfaces (above eth0) to alert
switches to open up multicast in that direction. Not many managed
switches have support for this yet.
Also, see the smcrouted -c SEC option for periodic flushing of learned
(*,G) rules, including the automatic blocking of unknown multicast, and
the smcroutectl flush command.
SMCRoute should in theory work on any UNIX like operating system which supports the BSD MROUTING API. Both Linux and FreeBSD are tested on a regular basis.
On Linux the following kernel config is needed:
CONFIG_IP_MROUTE=y
CONFIG_IP_PIMSM_V1=y
CONFIG_IP_PIMSM_V2=y
Check the list of multicast capable interfaces:
cat /proc/net/dev_mcast
On *BSD:
options MROUTING # Multicast routing
options PIM # Enable for pimd
As of SMCRoute v2.2, the libcap library is required for full privilege
separation using POSIX capabilities. At startup this library is used to
drop full root privileges, retaining only CAP_NET_ADMIN for managing
the multicast routes. Use --without-libcap to disable this feature.
$ ./configure
$ make -j5
$ sudo make install-strip
The configure script and the Makefile.in files are generated and not
stored in GIT. So if you checkout the sources from GitHub you first
need to generated these files using ./autogen.sh.
Note: On RHEL/CentOS 6 you must configure --without-libcap
SMCRoute is maintained collaboratively at GitHub. Previously the code was hosted and maintained by Debian at Alioth and before that by Carsten Schill, the original author.