Any network provider which is using multiple ANS/NSFNET connections to split load should have an addressing plan that assigns a different aggregate to each exit point. The basic rule is: for each routing policy you have, you should have different CIDR block. I thought we'd been over this in at least the Regional Techs forum before.

I have actually been aiming towards supporting having one's cake and eating it too, with route colouring. That is, a neighbour who wanted to split their load between several direct gateways, but who also wanted to advertise a provider aggregate, would advertise the aggregate route plus enough more specific routes to get us to the correct gateway. We would colour the more specific routes not to be advertised to anyone else, so only the aggregate route would be propagated elsewhere. This isn't quite done yet, but it is being worked on. This assumes, of course, that everyone else pulls enough routes out that we have the luxury of forwarding table space to support this. I suspect a 32M RS/6000 can carry a bigger routing load than a 16M cisco but not a whole lot more, so if we get to the point where 16M ciscos are crashing-and-burning more frequently we'll also be looking for ways to shed routing load. I think we're getting perilously close to a time when there will be no time to experiment with this stuff, it'll be do, or die, or make your router vendors very wealthy ordering upgrades. In fact the way things are going I sort of wish I'd found a job with a router vendor rather than an operator. Dennis Ferguson

A lot of the regional networks have more than one attachment point to ANSnet. Some use one as primary and one as backup. Most of the regional networks announce some of their networks as primary at one attachment point and other networks at another attachment point. This means that that regional could not aggregate before reaching ANSnet because to do so would mean losing the load balancing. One longer term way around this is to have ANS accept more specific routes plus an aggregate and propogate the more specific routes into it's IBGP but not propogate them further (just the aggregate).

Is this really a common case? BARRNet has two attachments to ANS/NSFNET, but they are strictly primary/secondary, so the same aggregates will be advertised at both locations.

PREPnet is planning to put such a scheme into place in the near future.

Any network provider which is using multiple ANS/NSFNET connections to split load should have an addressing plan that assigns a different aggregate to each exit point. The basic rule is: for each routing policy you have, you should have different CIDR block. I thought we'd been over this in at least the Regional Techs forum before.

Unfortunately, PREPnet already has a CIDR block half allocated, and it doesn't match the policy needed to do traffic splitting into ANSnet. It would be wise to do this, but only when you can foresee what the policies will be in advance. If you can't guess what your policy will be in the future... I'm sure Noel would have inspiring comments to make about re-addressing at this point. --Jamshid