[Olsr-dev] olsr 0.5.6-r8 ipv6 multicast

[Henning Rogge]

Am Dienstag 09 Februar 2010 19:37:49 schrieb John Hay:
> Hi,
> 
> I am trying out r8 (with FreeBSD and IPv6 as usual) and ran into a few
> surprises. I see the default multicast address is now ff02::1 and not
> ff0e::1 anymore. I think it is better, but it is going to be fun moving
> our networks. :-)
ff02::1 is the universal "all nodes linklocal multicast".

Some commits ago (after 0.5.6-r8) we changed it to ff02::6d (manet-router 
linklocal multicast).

ff0e::1 would be a global scope multicast IP, which would be a desaster for 
OLSRd. OLSR routing messages MUST not be forwarded beyond one hop by the ip 
stack.

> I tried setting the multicast address with "IPv6Multicast ff0e::1", but
> I did not get packets out of the interfaces. Looking into it, I see that
> there is now two sockets for each interface, one to receive and one to
> send on. I think the problem is that join_mcast() is only called for the
> receive socket, so setsockopt IPV6_MULTICAST_IF is not set on the
> transmit socket. An interesting thing is that ff02::1 work properly as
> it is, probably because the kernel handle link-local multicast special.
Yes, that might be the case. Don't use anything beyond linklocal scope for the 
OLSR multicast IP.

> So what should one do? I think join_mcast() is a bit heavy to use for
> the transmit socket, maybe we should have another function that only
> set IPV6_MULTICAST_IF?
If this is necessary for BSD you could send a patch. But it might create a 
non-working OLSR mesh.

> Another question, is there a way to receive olsr commit messages via
> email?
Sorry, not at the moment... maybe we could hack something together, but it 
would be a little bit complicated with the multiple branches of our GIT 
repository.

Henning Rogge
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