> Classless aggregation is mostly an 'external' routing feature, insofar
> as private networks are concerned. The idea of classless aggregation
> is more of an 'internet end-to-end' routing mechanism, at least for the
> moment. While there are certainly valid (and valuable) methods for
> summarizing routes internally, we will begin to see more and more
> folks opting for RFC-1597 addressing internally, while announcing
> one or two valid networks (or CIDR blocks) to the Internet community.
> I totally agree with Bill in that people really need to stop thinking
> of IP address space as classful, and beging to think of it as classless.
> The down-side to this is that there are thousands of networks using
> classful routing internally and unable (for whatever reason) to use
> BGP(4) to summarize and announce aggregate networks to the remainder
> of The World. Most of this summarization is now being done by the
To give you some idea of hacks possible with routing, I've setup 6
subnets using 26/6 (I have to use Unix boxes to route between these),
using static routrs, and advertise these to the cisco as three 24/8
routes (a single CIDR block/mask wouldn't work either because of the
numbers involved :-(). Oh, I announce the three routes using RIP :-)
The biggest problem, currently, with using anything other that class
based routing inside a Unix box is that *VERY FEW* support classless
routes. The only versions of Unix where I know it is possible are
those based upon NET-2 (ie BSDI/NetBSD/FreeBSD).
p.s. why was this on firewalls ? I assumed it was on an ID*R list.