Re: A tunneling proposal

[Iljitsch van Beijnum <iljitsch@muada.com>]

On Mon, 16 Jul 2001, Ramakrishna Gummadi wrote:

> > Tunnels can fix some types of failures, but they can't fix every type of
> > failure, like routing problems that affect the entire ISP. This kind of
> > multihoming is clearly inferior to the regular IPv4 way.

> One of the  primary goals of tunneling, I think, is to make *existing*
> connections that use transports such as UDP and TCP survive a partial
> outage within the ISP.

Yes, tunnels can be useful for this.

> True, regular IPv4  multihoming can provide this facility only because
> end-hosts use a
> single non-aggregatable address that is announced in the DFZ.

Well, maybe this is just the way things will have to be.

Is there a known limit to the number of routes in the global routing
table? I know bad things started to happen at about 4000 and 10000, but
obviously those problems have been solved. Routers run just fine with 100,000
routes at present, and unless I'm mistaken, the most common types of router
have CPUs and memory that are well below what most of us have in our desk top
PCs.

On top of that, each route takes a LOT of memory: 240 bytes for the routing 
table and for each peer route in the BGP table in a Cisco.

If we can both increase memory and decrease the route/BGP table entry size by
an order of magnitude, we should be able to run with a global routing table
of 10,000,000 routes. That's about the entire IPv4 space as individual /24's.

Link speeds are high enough, and if route lookups are implemented as
variations of binary search they are of an order log(n) so going from 10e5 to
10e7 should be just a 40% slowdown. The only thing that might be a problem is
processing so many routes when BGP sessions come up.

I think it's worth it to look at this, because with CIDR it is pretty much
impossible to efficiently route traffic: many locations are hidden behind
aggregates. Someone in Chicago has to choose between routing traffic for the
aggregate to the west coast or the east coast, and in either case some
traffic will have gone in the wrong direction.

Iljitsch van Beijnum