Subject: Re: Comment on ISIS extensions for traffic engineering

From: Radia Perlman - Boston Center for Networking <[email-masked]>
Date: Thu, 5 Aug 1999 13:44:30 -0400 (EDT)

> Has the processing power on routers outpaced the
> growth in subdomain size sufficiently that this optimization is
> no longer necessary?

I don't believe that optimization was ever necessary.
If there is enough time
to calculate a tree with an O(E) algorithm, then there's
enough time if it's O(Elog n). Documenting it
and asking a customer to make a choice is just making it way
more important than it deserves to be. Encouraging anyone to
stick with the old option will cause interoperability problems to
persist for longer.

It would be nice if within a few years this option just completely
replaces the current one. I wouldn't want to see them both
carried around in the documentation forever, with a note about how
if you choose the 6-bit metrics, you'll be trading off computation
time of SPF vs flexibility. We're just replacing the option because
this one is better. It doesn't waste room reporting 4 metrics and
it has a larger field. I'd recommend just saying that the old one
is there temporarily for backward compatibility, but we are
migrating to the new one.

The 6-bit metric is my fault, of course. Sorry about that.
The only reason I did it was because
it was my manager who had thought up the log n optimization, so it seemed
expedient, :-) even though even at the time I thought the optimization was
not important. I rationalized that 6 bits would be OK, but that was
because I was assuming the only costs reported would be of links, rather
than entire paths.

Radia

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From: Paul Traina <[email-masked]>
Date: Thu, 5 Aug 1999 11:00:12 -0700

Thank you for the breath of sanity.