UDP multicast using winsock API differences between XP and Vista

Question

It seems to be that the implementation required to set up a UDP multicast socket has changed between windows XP and windows vista. Specifically:

• Under windows XP, you must call bind() before you can reference any multicast-specific socket options.

• However, under windows vista, you must not call bind() when dealing with multicast sockets.

Failing either of these two points results in a socket error at runtime.

Am I going crazy, or have other people seen this as well? Is there a better solution than conditional compilation of the bind() call?

Answer 1

What error are you getting from the setsockopt() call that you make to apply IP_ADD_MEMBERSHIP and join the multicast group?

I've just run some tests here with my server framework and I note that I DO call bind() on Windows 7 (I don't have a Vista box to hand) and I can then also join a multicast group as expected as long as both the binding address and the multicast address are valid.

However I cannot call bind() with INADDR_ANY, as that causes the joining of the multicast group to fail with error 10022 (WSAEINVAL) and if the multicast group address isn't a valid multicast address the call fails with error 10049 (WSAEADDRNOTAVAIL). Which all seems fair enough.

I'm booting an XP box now...

[Edited after testing on XP]

On XP it's legal to bind() to INADDR_ANY and it's legal to use invalid multicast addresses. So, I expect, you're doing one of those and it therefore works on XP and not on Vista/Win7.

So, what error are you getting and what address are you binding to?

Answer 2

I don't know about this specific question, but I do know that the network stack was rewritten from scratch for Vista