On Sat, 23 Jun 2001, Eric Oosting wrote:
Under what circumstances would the assumption (that an AS should always advertise a route to the source address of packets it transmits) not be a good one?
Assymmetrical routing is a good one (see the reference Roland Dobbins posted for part of the story). Half the networks here are advertised out of different places from which the packets leave. This is mainly due to having one way satellite links. Sure the networks are advertised somewhere, but it's on the other side of the world (and to a bunch of different providers) from where we send the packets to you. Another one we have is a pop with a small link and larger link. To make some use out of the small link you might advertise only some networks at the pop. But at the same time outgoing traffic from any of the networks at that pop may go out that link. Sure you could prepend everything half a dozen times but some people ignore prepends for directly connected peers so this won't work (we tried it, we know). Another point, if people are going to have filters then they MUST have a quick and easy way for this filters to be changed and to propogate everywhere quickly. People who insist that you provide an exact list of what you want to advertise (with the exact prefixes) and then take a week to process any changes (or 12 hours for that matter) should have prices to match their discount level of service. -- Simon Lyall. | Newsmaster | Work: simon.lyall@ihug.co.nz Senior Network/System Admin | Postmaster | Home: simon@darkmere.gen.nz ihug, Auckland, NZ | Asst Doorman | Web: http://www.darkmere.gen.nz