Subject: Re: gre(4) and multicast
To: None <>
From: Gert Doering <>
List: tech-net
Date: 05/14/2005 11:41:27
In Miles Nordin wrote:

>I'm trying to run OSPF (IPv4 and IPv6) over NetBSD's gre(4), and it's
>not working.

>On the following machine, ezln, Quagga's ospf6d is listening on both
>tlp4 and gre0.  tlp4 is an Ethernet with another OSPFv3 router on it,
>and gre0 is a tunnel to lucette.  When I ping the OSPFv3 multicast
>address on tlp4, both routers answer, but over gre0 I get no answers.

>It could be a quagga bug, but since the NetBSD gre(4) v6 support is so
>new and I know others are using Quagga/gre successfully, I thought a
>lingering gre multicast bug was pretty likely, and I'd ask here if
>someone recognizes this as a quick-fix.

I don't think it's a problem specific to gre(4), as the gre/v6 support
was done very much in line with the way gif(4) does it.  Or, to phrase
it differently: could you try changing the gre(4) tunnel to a gif(4)
tunnel, and see whether all-routers multicast works there?

I'm not really sure how the all-routers multicast address is handled
internally.  Is it possible that it answers only if the ospfd is
running, and has registered on all interfaces where it wants to 
setup neighbour adjacencies?

>it's just that lucette doesn't feel inclined to answer them.  I
>noticed another odd thing, but I think it's unrelated.  If I use
>pkgsrc tcpdump on the unicast ping, the ping that lucette _does_
>answer just fine, I get:

Does it work with the system tcpdump?  If yes, it looks like a PR on the
pkgsrc tcpdump would be a useful thing...

>ezln:~$ ping6 ff02::1%gre0
>PING6(56=40+8+8 bytes) fe80::200:f8ff:fe77:8168%gre0 --> ff02::1%gre0
>16 bytes from fe80::200:f8ff:fe77:8168%gre0, icmp_seq=0 hlim=64 time=0.889 ms
>16 bytes from fe80::203:baff:fe0f:aa45%gre0, icmp_seq=0 hlim=64 time=2.208 ms(DUP!)

Now this hints at "basic multicast stuff over gre(4) is working", so
maybe it's really the "ospfd doesn't register on gre0" thing.  (Pure
guessing, though).

--   fax: +49-89-35655025

Inspiration without perspiration is usually sterile.