I was having lots of problems last night and this morning with multicast not working correctly on a linux host. As soon as I started tcpdump multicast would work. It is not fun trying to troubleshoot a problem that goes away everytime you try to debug it.

Turns out the realtek r8169 driver doesn’t handle multicast on the newer cards correctly.
Downloading the r8168 driver from Realtek and installing it resolved the issue.

This post is being made so that google will be able to help the next person with this problem.