Hey all,

This is my first post so hopefully this isn't too dumb of a question. My problem is this:

I am interfacing to an old system that broadcasts data via UDP on a fddi ring. I cannot change this fact, so I am stuck with it. I have code that runs on a HP that receives the data just fine (This is an old HP). I have moved over to the linux side of the house (Suse 8.1) and I run into the problem that I think the broadcast data is being filter out by the kernal (?) and I think it has to do with multicast...

Here is what I know: My fddi card is setup correctly (using a DEC DEPFA fddi card). If I do a tcpdump on the fddi card, I can see data coming from the desired port number. I can bind to the port number, but when I call select() I never return without a timeout. I have the addr set to INADDR_ANY and I have verified that I am on the correct port. So either I am missing a special socket option that will let the data through or the way the kernal deals with the UDP protocol has changed. The only thing that I can think of that would have changed with the UDP protocol and how it is handled is multicast. I have tried to reconfigure the kernal to disable multicast, but those efforts seem to have failed.

If you guys (and gals of course) have any insight onto how I can disable this multicast "filter" as I suspect, it would be greatly appreciated. Thanks in advance!

When all else fails, firewall it out. use iptables to disable all incoming/outgoing packets to Class D networks.

I don't know if you've tried this, but there are parameters that can be passed to the kernel at runtime which allow you to turn on/off different features, such as multicasting. One of them is /proc/sys/net/ipv4/conf/<your-interface>(such as eth0, etc.)/mc_forwarding. Some information on that is found here (do a find in your browser for the mc_forwarding) and here.

I don't know if that's what you're looking for, but there you go.