Gordius has left the building. Was: RE: The Gorgon's Knot.

[Bender, Andrew]

Deepak Jain wrote: 

> The problem is where the RIB, or forwarding table is exported to 
> the line cards which frequently have less than 128MB of usable 
> RAM/SRAM/memory storage/etc. This essentially means that the line 
> cards can only directly talk to other line cards for a specified, 
> limited number of routing prefixes. I do not know the algorithms 
> used when the line card is out of memory, but in many cases this 
> memory is not field upgradeable beyond a certain point.

Srinivasan, Vargese, and others have demonstrated / observed that space
is not a material problem for the architecture you describe. Rather, it
is the time to complete a longest-match (or equivalent) operation for
each forwarding event, especially for high(er) interface speeds.

Regardless, 128MB is a LOT of table memory, especially when it is
virtually unknown to see anything larger than 10-20Mbit CAMs; prior to
reduction / expansion / etc, there's scarcely 11B of unique information
in an IPv4 route. Adding in some bytes for mysterious 'other stuff',
this is easily 4-8MM routes. We'll have to see another knee in route
proliferation before this becomes a problem, and space exhaust would
most certainly prevent this from happening. 

> Many smaller networks can and do use PCs for BGP and for 
> forwarding because their total forwarding needs at their core are 
> say sufficiently less than 800mb/s upto which PCs seem to handle. 
> However, the desires and models of these smaller networks don't 
> scale much beyond this level with currently available PC 
> technology.

Agreed... as regards PCs lets remember that history has offered certain
commentary on the non-role of PCs (indeed general purpose computers) in
network infrastructure... viz. there aren't many GRFs / DDP516Rs / etc.
around anymore. I doubt this is an 'interesting problem' for the op or
planning community. 

Regards,
Andrew Bender
taqua.com