We had a multicast solution until we upgraded to 2.6.24.5 and 64 bit dual core CPU. We also added a second NIC. The kernel was built with IP_MULTICAST,IP_ADVANCED ROUTER,IPIP,IPGRE,IP_MROUTE == *. The terminal receives all unicast messages, does join the multicast group, even occassionally send the multicast report to the group address. I can see messages come into the eth0 but the kernel never forwards them to the waiting socket/process. I've added smcroute but nothing changed. Does anyone have this type of issue? IPtables firewall was not built into this release.
Thanks in advance.

Traced the problem to bind. In the original working code, sa.sin_addr=htonl(INADDR_ANY) the bind was was done to 0.0.0.0. With the additional of another NICs multiple binds are done with each using the IP address of it's own interface ...sa.sin_addr=inet_addr(eth0_ip_addr) or eth1_ip_addr. And then the bind(); called.

The next step is to call setsockopt(). We did leave the new setsockopt with the individual IP address for each different interface. Seem to work fine now.

Question remains .. why can't I bind to an individual address?