links on the blink (fwd)

Paul A Vixie paul at
Fri Nov 10 03:46:23 UTC 1995

I have no idea how those two blank messages got out.  My apologies.

> Ideally, the capacity of LAN *attachments* (not the total bandwidth
> of the LAN switch!) should be about the same as the capacity
> of backbone links, multiplied by the number of backbone links attached
> to each backbone router.

Agreed, which is why the GIGAswitch works and why, once Cisco has a reasonable
100BaseT interface processor, a Grand Junction will work.

> Anyway, that boils down to the LAN switch being the single point
> of failure.

Statistically speaking, the things that go wrong with modern machines that
have no moving parts are usually software or configuration related.  Since
the LAN switch is mostly hardware with a little bit of bridging and spanning
tree stuff, it is a lot less complicated than the average router.  I think
router software and configuration errors are going to pretty much drive the
failure rates for the next few years.  I'm not worried about the LAN switches
since there are so many worse/nearer things to worry about.

> All in all, the backbone router should be scalable to the point that
> it does not need any clustering; and redundancy is provided by
> "internal" duplication. 

Agreed.  I had a conversation over coffee a few months ago and this topic
came up; my conclusion was that we were in for a really rough ride since each
previous time that the Internet backbone (or the average high end customer)
needed more bandwidth, there was something available from the datacom folks
to fit the bill.  (9.6 analog, 56K digital, 1.5M digital, 45M digital.)
Furthermore, the various framing and tariff issues moved right along and have
made it possible to provision Internet service in ways that would have made
no sense just a few years ago (witness frame relay and SMDS.)

But this time, we are well and truly screwed.  The datacom people have
gradually moved to the "one world" model of ATM, and have put all their
effort behind the mighty Cell.  They thought their grand unification of
voice, data, VOD, etc, was finally a way to stop dinking around with lots
of incompatible systems and oddball gateways (those of you who have tried
to get inter-LATA ISDN or international T1/E1 working know what I mean).

So the datacom community's answer to the Internet community is "if you're
not able to get what you need from T3, use ATM which will be infinitely
scalable and can be used as an end-to-end system."  Who knows?  If DEC can
make a 90MHz NVAX chip after some PhD somewhere "proved" that the multibyte
instruction encoding made certain kinds of parallism impossible and that
the fastest VAX would run at 60MHz, and if Intel can make a sewing machine's
CPU into a 64-bit monster with three kinds of virtual memory, then perhaps
the ATM folks can figure out how to do all the lookasides and exceptions
they need to do in their little itty bitty hundred-picosecond window.

But I don't think so.  I think we are going to have to get clever, and that
we have used up our bank account of times when brute force coming out of the
sky can save us.  This time, gentlemen, the calvary is not coming.  As much
as I despise the topic Matt and Vadim have been discussing today, I think
we're looking at some kind of load sharing.  Probably static load sharing
with no adaptation to traffic type or flow, since as Jerry pointed out a
few weeks back, that's a slippery slope and a lot of people have died on it.

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