Re: [Isis-wg] [rbridge] Why is MTU discovery important?

[Donald Eastlake <d3e3e3 at gmail.com>]

2009/4/11 Dave Katz <dkatz at juniper.net>:
> As someone who as been designing and coding this stuff since before most of
> our current crop of engineers were born, I'll throw in some practicalities:
> 1)  The thing we call "IS-IS" that has a NLPID of 0x83 (IIRC) can only be
> changed in an upward-compatible manner.  So any proposal to change anything
> in the existing L3 IS-IS beyond the addition of a new PDU type is a
> non-starter (and even that is likely to break some dubious implementations,
> which may or may not be a bad thing).

Yes, the IS-IS NLPID is 0x83. I believe changes beyond the addition of
PDU / TLV / aub-TLV will be needed.

> 2)  If TRILL ends up as a distinct protocol (by NLPID or some other
> mechanism) it can do things any which way it pleases.  It is best from an
> implementation perspective to keep it as close to IS-IS as possible so that
> a single implementation with a few checks here and there can do both.  This
> has the added advantage that foolish implementors will cut-and-paste the
> code and create themselves maintenance problems and allow Darwinian
> selection to occur, like back in the NLSP days.  ;-)  But it is entirely
> possible to share 99% of the code while maintaining protocol "distinctness."
>  And having it distinct from IS-IS avoids having to be forced to make
> compromises to avoid breaking IS-IS (at the cost of less common code).

I think it is probably a good idea for TRILL IS-IS to have a different NLPID.

Donald

> Just my 112 ZMK.
> --Dave
>
>> ...
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