Re: ND NS/NA support required on point-to-point links?

[Mark Smith <[e-mail]>]

On Wed, 14 Jul 2010 15:25:54 +0200 (CEST)
[e-mail] wrote:

> > >However, it would seem that several of the major vendors (e.g. Cisco,
> > >Juniper) have interpreted this differently, and chosen not to perform
> > >ND on point-to-point links.
> > 
> > Do you mean perform, as in issue the NS request or also in not responding
> > to a NS request from the peer?
> 
> I have no idea whether an NS request would be answered on a point-to-point
> link for these vendors. When I have tested this in the lab, the observed
> behavior is that an NS request is never issued.
> 

It's also a bit interesting to look at the multicast groups that have
been subscribed to on the interfaces. Some of the
implementations subscribe to the solicited node multicast group(s) for
the local addresses. It's as though they're "half" ND NS/NA enabled.

> > So I wonder, with all the IPv6 interoperability testing and certification
> > going on, how come nobody ever noticed that this is an issue?
> 
> The ping-pong behavior on IPv6 point-to-point links has most certainly been
> noticed, see for instance
> 

It seems the the consequence of not implementing ND NS/NA on
point-to-point links has been noticed, not the root cause. The root
cause seems to be an assumption that any non-local interface addresses
on the link within a prefix must exist and are always available at the
other end of the point-to-point link, so traffic can be forwarded onto
that link without validating that assumption. When implementations at
both ends of the link are making that assumption, the ping pong problem
is the result.



>     http://tools.ietf.org/html/draft-ietf-ipngwg-p2p-pingpong-00
>     http://tools.ietf.org/html/draft-kohno-ipv6-prefixlen-p2p-00
>     http://www.janog.gr.jp/meeting/janog22/program/day2/data/day2-1-e.pdf
> 
> Steinar Haug, Nethelp consulting, [e-mail]