I have this issue with our SLES 11 SP1 systems.

App 1 on eth1 is multicasting messages
App 2 on eth2 is multicasting messages
But App1 cannot pickup the messages sent from App2

If I have App1 and App2 both binds to eth1, App1 can pickup the messages without issue.

Any idea? any suggestion is welcome to trigger more thought and digging.