RE: Draft: PI addressing derived from AS numbers

On Sun, 2 Feb 2003, Pekka Savola wrote:

> For example, consider (in future) 10,000 routes coming behind a
> next-to-the-origin-AS ISP.   If something bad happens to the ISP, all
> 10,000 routes will be withdrawn, and a secondary path will be selected
> (perhaps 3,000 will go to ISP X, 3,000 will go to ISP Y, and 4,000 go
> nowhere, simplifying).

> The absolute numbers _might_ be manageable if changes were manageable: I'm
> fairly certain of that at least to the degree of O(10^6) -- memory is
> cheap.

I assume you mean 10^6 number of routes? Cisco's CEF seems to take
something like 300 bytes for a single route. That makes for 300 MB
worth of fowarding tables, which wouldn't stress current technology too
much.

BGP and routing table entries also seem to be something like 300 bytes
each, so for the main route processor the amount of memory could be
somewhat more problematic. But 4 copies of each route in the BGP table +
1 in the routing table would make for 1500 MB, also still doable.

> A way to make changes manageable could be to change how BGP works with
> regard to nested routes from multiple sources.  Or really, devise another
> protocol.  Here's a raw thought:

> When BGP is used for multihoming, all the paths are advertised throughout,
> not only the current best paths.  There has to be a marking on which ones
> aren't the best paths of course.  When a transit AS becomes unreachable,
> instead of withdrawing the routes and waiting for updates, the only thing