What is the limit? (was RE: multi-homing fixes)

Wed Aug 29 23:08:11 UTC 2001

On Wed, 29 Aug 2001, Sean M. Doran wrote:

> | I think there is real promise in SMP though.  There are many SMP
> | applications that scale near linearly, and I think properly designed
> | routing can be one of them.  If a linear SMP solution can be found
> | then there is at least one way to scale the routing infrastructure
> | to near infinate size simply for $$$'s.
> 
> So like I have to hop on a plane, but the Russian guy wakes up
> really soon, and this is very much his field...  :-)
> 
> You won't like the answers though, 'cause they're consistent
> with mine.  Oh well.

Hmm. Actually, routing info processing parallelizes fairly well.
Computationally heavy things like policy evaluations and BGP protocol
engines are generally done on per-peer basis, so you can do it on a bunch
of processors in parallel; the path comparison (aka best route selection)
is done on per-prefix basis (i.e. the best path for each prefix is
generally independent from all other prefixes) - so it can be segmented by
address blocks (i.e. one processor does path selection for 0/2, the second
for 1/2, the third for 2/2, the fourth for 3/2; etc; you got the idea :)

That said, implementing heavily parallel routing software in practice is
quite hard.  Even non-parallelized routing code is not easy to do right,
as was convincingly demonstrated by OFRV.

The approach I advocated when starting Pluris was to dramatically reduce
topological complexity of networks instead by having only one large
(internally redundant) IP router per POP instead of clusters of smallish
boxes.  I still think this is the best approach, because it improves not
only exterior routing performance (smaller iBGP meshes) but also interior
routing.

Like, Keep It Simple :)

--vadim