Re: (ngtrans) NUD for ISATAP Routers

["Fred L. Templin" <ftemplin@IPRG.nokia.com>]

Karen,

Karen E Nielsen (TED) wrote:
> What I do not understand is why an Isatap ROUTER in the "base specification"
> SHOULD perform NUD in accordance with 2461 on it's Isatap hosts, when we agree that
> this mechsnism is broken and for ROUTERS amounts to nothing (except for overhead).
> I would suggest either to omit this requirement for ROUTERS or then at
> least describe how the NUD mechanism from 2461 should be altered in order to
> make it meaningful (and scalable) for a ROUTER.

I believe what you are saying is consistent with our intended
meaning. But, the text in the draft seems to be coming across to
you as too restrictive and this was not our intention (Tim, Mohit,
or Dave - please let us know if you disagree.) Let's look at the
two elements of section 5.1 that may be causing confusion in
more detail:

   Protocol addresses (IPv6) in ISATAP are resolved to link-layer
   addresses (IPv4) by a static computation, i.e., the last four octets
   are treated as an IPv4 address.

I do not believe there should be any confusion in what is being
said here, but what is *not* said is whether/not the node should
send NSs and wait for NAs at the time the static computation is
done. This seems to me to be an implementation alternative that
may provide faster unreachability detection in some cases, i.e.,
it is not required for interoperability. Perhaps a sentence could
be added to the effect of "Nodes MAY send NSs and wait for NAs
when performing static computation." I personally don't believe
this is needed, but I could possibly be convinced otherwise.

   ISATAP nodes SHOULD perform Neighbor Unreachability Detection (NUD)
   as specified in [DISC, 7.3], and MUST send solicited neighbor adver-
   tisements as specified in [DISC, 7.2.4].

The "SHOULD" here seems to be your bone of contention, and I can
understand your concern. But, I believe we were intending a looser
interpretation of the SHOULD, based on our earlier discussions on
NUD for routers. Perhaps a slight re-wording such as the following
could help disambiguate things:

   + ISATAP routers MAY and ISATAP nodes SHOULD perform Neighbor
   + Unreachability Detection (NUD) as specified in [DISC, 7.3].
   + ISATAP nodes MUST send solicited neighbor advertisements as
   + specified in [DISC, 7.2.4].

Does this address your concerns?

Fred
ftemplin@iprg.nokia.com