The IP Over NBMA (ION) Archive

[Albert Manfredi <manfredi@engr05.comsys.rockwell.com>]

gja@bellcore.com wrote:

[ ... ]

> Please - to encourage clarity of people's understanding of the issues
> here I'd like to see an end to this bogus association of NHRP with
> multicast (cut-through or otherwise).

Interesting point. Which says we need MCNHRP, or ...

> NHRP addresses a palpable need people have to dynamically bypass
> topological mismatches between IP unicast paths and underlying
> ATM paths. That is all. (It is only of secondary importance that
> you reduce the number of reassembly/segmentation hops.) In so far
> as it achieves this need, it is a good thing. However, it is
> also worth remembering that if you minimise your topological
> mismatch, you reduce the need for unicast cut-throughs (regardless
> of the name of the protocol you use to discover them).

Re your last sentence, a point worth emphasizing. Also, if you _abolish_ 
your topological mismatch, ...
 
> The issue for multicast cut-throughs is not whether you can conjecture
> a use for them, but whether it is worth the effort to construct and
> manage them.

A philosophical point: when RFC-1112 was written, a very well-defined 
mapping between IP multicast addressing and the underlying medium's own 
scheme was developed. This situation is not entirely different. At that 
time, Ethernet with its own scheme existed, and IP was the new kid on the 
block. This time, IP and its scheme exists and ATM is the new kid on the 
block (wrt multicasting).

I get the continuing sense that we're trying to solve problems the 
hardest possible way. Let's ask Steve Deering whether he thought of using 
a multicast resolution server while developing RFC-1112.

Bert
manfredi@engr05.comsys.rockwell.com