RIPng advertisement hop count 1 (should be 255 per RFC)

[Simon Dickhoven]

OK. I looked at proto/rip/rip.c a bit more and figured that I might as 
well give it a shot and hack around a little bit. I ended up making this 
tiny mod:

--- a/proto/rip/rip.c
+++ b/proto/rip/rip.c
@@ -706,7 +706,11 @@
    rif->sock->dport = P_CF->port;
    if (new)
      {
+#ifndef IPV6
        rif->sock->ttl = 1;
+#else
+      rif->sock->ttl = 255;
+#endif
        rif->sock->tos = IP_PREC_INTERNET_CONTROL;
        rif->sock->flags = SKF_LADDR_RX;
      }

Subsequently, I did a full Debian package build based on

http://backports.debian.org/debian-backports/pool/main/b/bird/bird_1.3.7-1~bpo60+1.diff.gz

I added the above patch to the debian/patches dir and appended the patch 
file name (I named it "011-ripng_hopcount.patch") to debian/patches/series.

The package built fine. I installed it on my test box and lo and behold: 
Vyatta/Quagga is now happy and I'm seeing my IPv6 routes propagate via 
RIPng.

Tcpdump reveals that RIP(v2) is still using a TTL of 1 and RIPng is 
using an HLIM (IPv6 equivalent of TTL) of 255.

Thanks.

- Simon

On 06/14/2013 03:04 PM, Simon Dickhoven wrote:
> Hi,
>
> I just started experimenting with BIRD for an IPv6 deployment. I am
> using Vyatta VC6.6R1 router VMs on either side of my BIRD VM (which runs
> on a customized Debian Squeeze release with kernel 3.3.1). I installed
> bird/bird6 1.3.7 from the squeeze-backports repository.
>
> Here my setup.
>
> Lab Net --- Vyatta --- BIRD on Debian --- Vyatta --- Stub Net
>
> Anyway, I don't have any problems with my configs or anything like that.
> My problem is that Vyatta's ripngd (part of Quagga) complains about an
> RFC violation when it receives RIPng advertisements from BIRD:
>
> Jun 14 21:43:40 vyatta ripngd[1682]: RIPng packet comes with non 255 hop
> count 1 from fe80::20c:29ff:fef8:cbc5
>
> I looked at the source code in rip.c and see this line:
>
>         rif->sock->ttl = 1;
>
> which is the only reference I can find to TTL/Hop Count. So I'm guessing
> this is the culprit. The latest source code (1.3.10) is identical in
> this respect.
>
> RFC 2080 states
>
> [...]
> As an additional check, periodic advertisements must have their hop
> counts set to 255, and inbound, multicast packets sent from the RIPng
> port (i.e. periodic advertisement or triggered update packets) must be
> examined to ensure that the hop count is 255.
> [...]
>
> The use of the term "must" leads me to believe that this is not optional
> and is therefore required for RFC-compliance.
>
> There seems to be no such requirement for RIP (v1/v2) so simply changing
> the source code to indiscriminately set the TTL to 255 is probably not
> the right thing to do.
>
> Have others encountered this problem and is there possibly a patch or
> something for getting RFC-compliance and hence interoperability with
> Vyatta/Quagga(ripngd)?
>
> Thanks.
>
> - Simon
>