Testing Multicast Traffic on Linux

multicast-on-linux.md

Testing Multicast Traffic on Linux

Prerequisites

By default Linux ignores Broadcast and Multicast ICMP messages. That's why you need to enable it first:

sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=0

Join and Test Multicast Traffic

To join any mutlicast address (e.g. 224.10.10.10/24) just add it to your active interface (e.g. eth0) and append the keyword autojoin at the end:

ip addr add 224.10.10.10/24 dev eth0 autojoin

Now you can verify the join:

ip -f inet maddr show dev eth0

Finally to test the Multicast communication, ping to the chosen IP address from another host:

ping 224.10.10.10

You should now get an answer from your Multicast enabled host. That's it.

Change IGMP Version

The Linux Kernel normally uses IGMP version 3 to join Multicast groups. If you would rather use IGMP version 2, just change it via the command down here:

echo "2" > /proc/sys/net/ipv4/conf/eth0/force_igmp_version

Multicast Group Join Inside Docker Container

In order to get the commands above here working inside a Docker container, it must be started with the Linux capability NET_ADMIN:

docker run --rm -it --cap-add NET_ADMIN alpine /bin/sh

Fun fact: GNS3 starts all containers with all Linux capabilities added and in priviledged mode.

Be sure to start a multicast ping from another host and the one from which you've bound to the multicast address. Also be sure to issue ping -t 16 224.10.10.10 otherwise all packets will leave with a TTL=1.

still seeing "connect: Invalid argument" after adding "-t 16" argument to ping

is multicast correctly enabled on your system ?

do you mean set "sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=0"?

yes, the command given above works well on my ubuntu.

I see. Maybe there is some issue on my end. Thanks Surya