Re: Dual Homed BGP

[Tore Anderson <tore () fud no>]

* Baldur Norddahl

> If you join any peering exchanges, full tables will be mandatory. Some parties will export prefixes and then expect a 
> more specific prefix received from your transit to override a part of the space received via the peering. 

That would be a fundamentally flawed expectation, in my opinion.

An AS that that advertises a prefix to its peers must be prepared to carry traffic to that entire prefix via that 
peering circuit.

There is simply no guarantee that a more-specific prefix advertised somewhere else will make it into the RIBs and FIBs 
of all the peers of that AS.

The AS might of course opt to do so anyway for traffic engineering purposes, but there is no assurance that it will 
actually work 100% of the time. When it doesn't, the AS in question would need to carry the traffic from the peering 
circuit across their own backbone.

If the AS in question for some reason cannot do so, it would need to adjust its advertisements across the peering 
circuit so as to avoid falsely advertising reachability to unreachable destinations.

Tore