[nsp] ospf default routes and bgp injection

[Neil J. McRae]

> As Nick mentioned, using OSPF to carry your infrastructure 
> networks (Loopback interface IP's mostly) and using iBGP to 
> carry your internal and customer prefixes is quite a scalable 
> approach.
> 
> Nick (sorry to post this in Oliver's thread), you're right. I 
> don't think I have seen a supporting document anywhere yet 
> (there could be, though), but this is something that has been 
> presented and agreed on multiple operators forums and 
> seminars that I've been a part of. 
> 
> It scales quite well and offers more features in terms of 
> filtering, flexibility and all. Just FYI, this is how I run 
> my backbone.

Over the past year or so we have been integrating the many
COLT ASes into AS8220. We have just completed one of the most
difficult parts which was caused by the former network carrying
customer routes in IGPs. Around 5000 routes where in the IGP
and every time we tried to do anthing including minor stuff 
IGP flaps killed us. We migrated these routes into BGP4 and 
management of the network became a million times simpler.

One gotcha is that you need to be aware of how you would do
high availiblity services, such as ISDN backup, dual homing
etc.

Neil.