The biggest problem with using non-routable ip addresses on numbered interfaces whether point to point or frame or atm or whatever, is that you lose outside connectivity from those interfaces. We tried this, but the essential traceroutes from our core routes are too important when debugging BGP problems to the outside.
Robert Bowman Exodus Communications Inc.
Exactly. Especially when you have downstream customers who only announce routes via BGP to you and/or other providers, it can be important for them to be able to trace out with a source address that has global connectivity. We usually use unnumbered interfaces, though, for singly-connected customers (unless their routers can't support unnumbered interfaces). The only major gotcha with that is that if they're using a Real Router (that deleted routes associated with interfaces that aren't available), you can't get to their router if their ethernet is down... Avi