[lwip-users] Re: multicast and lwip

[Leon Woestenberg]

Hello Jim,

(Jim wrotes this directly to me, I am copying this and my response to
lwip-users).

On Sat, 2004-07-24 at 00:27, Jim Gibbons wrote:
> I have gone over ip_input several times since reading your reply to
> William Wagner and I just can't see how an IP multicast packet will
> get this function.  I believe that it will have netif == NULL when the
> question /* packet not for us? */ is asked and will thus be dropped.
> 
> Your reply to William Wagner was very clear, though, indicating that
> lwip handles multicast reception.  Can you tell me how?
> 
You are totally right - quick investigation shows that lwIP in fact does
not handle incoming multicast traffic (it just is deleted).

However, the code I mentioned in my email to Williamm should still apply
to make multicast traffic pass the IP layer, and so have it end up in
the UDP/TCP PCB/socket layers, where you just bind your sockets to the
multicast address.

If we have that in place, we can add IGMP to actually inform routers of
our multicast reception wishes.

I hope someone picks this up as a small development project. Really,
lwIP has all the stuff available to implement multicast here, it just
needs some fairly trivial work.

Regards,

Leon.