HowTo: Add Multicast Routing to FreeBSD kernel

- 1 min read

This is a very short blog post, mostly intended as a reminder to myself. Basically, there are two methods of adding multicast routing support to the FreeBSD kernel:

  1. Rebuild the kernel with options MROUTING
  2. Load the kernel module: kldload ip_mroute

The kernel rebuild assumes the src.txz set was installed previously.

cd /usr/src
cd sys/amd64/conf
cat GENERIC | sed 's/GENERIC$/MULTICAST/' > MULTICAST
echo 'options   MROUTING         # Multicast routing' >> MULTICAST
echo 'options   PIM              # Enable for pimd'   >> MULTICAST
cd -
make kernel KERNCONF=MULTICAST
reboot

That’s it. Remember to make sure your Qemu VM has enough RAM or it will probably page fault on you. I use 1,0 GB RAM.

The other option, to load the ready made module, is likely better. But you want it to load at boot. So add this to /boot/loader.conf:

ip_mroute_load="yes"

To see what modules are available, check the /boot/kernel/ directory. There is, for instance also the IPv6 mrouting module:

ip6_mroute_load="yes"