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Re: Scalability issues in the Internet routing system

  • From: Per Heldal
  • Date: Wed Oct 19 07:20:50 2005

On Wed, 2005-10-19 at 09:31 +0200, Elmar K. Bins wrote:
> Susasn,
> > Using the compression ("cooking") per router can provide one level of
> > abstraction [reduction of prefix space] at router.  So cooking down your
> > Large number of routes to a "minimum" set of routes can provide some
> > leverage against the prefix growth.
> By cooking down the prefixes you unfortunately lose topology information
> which might be a bad thing, and at the same moment disrespect the site's
> wish to how it would like to be routed. Another bad thing, if you think
> of companies/sites paying for the entire network in the long run.

Don't expect an interest in your topology to reach much beyond your
peers. This isn't about prefix-aggregation, but about dropping
information from a router's memory that isn likely to be used. With many
peers you may have a large number of route entries for a given prefix
from which your router chooses one to be used and possibly
re-distributed to others. Ex: All that happens if you choose to only
keep the 2 best alternatives out of 5 or more is loss of redundancy in
case both the best routes are withdrawn. The algorithms used to select
the best path(s) remain unchanged.

> Apart from that, IMHO cooking down the prefixes only buys time, but does
> not solve the problem. More people will multihome, and with the current
> mechanisms and routing cloud, they have to do it by injecting prefixes.
> I'm not sure whether this hasn't long become an architectural question
> and should be moved to the (new) IETF arch list. Opinions?

Agree ... unless ....

> Yours,
> 	Elmi.
> PS: Btw, anyone can give me a hint on where to discuss new ideas for
>     e.g. routing schemes (and finding out whether it's an old idea)?

I'm aware of the new architecture list, but maybe the IRTF Routing
Research Group ( is an even more
appropriate place. From their charter:

  The Routing Research Group (RRG) is a group 
  chartered under the Internet Research Task Force 
  to "explore routing problems that are important 
  to the development of the Internet but are not 
  yet mature enough for engineering work within the IETF."

Of partial relevance to the recent discussion you'll find documents
there like a recent compilation of requirements for future