BGP TTL

[Geoff Huston]

This has been a concept that has floated round for some time as a way of 
limiting scope for some fine-grained advertisements.

The issue is that the network itself is quite dense (route-views sees an 
average AS path length of between 3 and 4.5 AS hops for each of the 
route-views peers) and the average AS path length for address prefixes is 
noted to be between 2.5 and 3.5 AS hops.

The question for me is whether a TTL has any practical scope limitation in 
such a richly interconnected environment.

Geoff


At 3/21/2002 06:38 AM, Andrew Partan wrote:
>A brief discussion over lunch brought up the idea of adding a BGP
>attribute - a TTL - to limit how far (by AS count) a route will
>propogate.
>
>I.e.: set TTL to 1 and your route only goes to your neighbors.
>Set TTL to 2 and it only goes to your neighbors and their neighbors.
>
>It might also help to limit the BGP ASPATH count-to-infinity problem
>when you withdraw a route (as you will only count to the TTL).
>
>This may not be useful in all cases but I suspect that it would be
>useful in enough cases that I think we should add this tool.
>
>         --asp