So it does not make sense for IBM or Sony to run dynamic routing in their internal networks?!?

Well.... it probably doesn't make sense for IBM or Sony to assign a different AS number to each router in their network and speak BGP between them. It's a matter of degree we're talking about here; of course it doesn't make sense to run full routing everywhere, just as it doesn't make sense to manually set up static routes everywhere. The point we're debating is what point along the line it makes most sense to set the slider. Most corporate networks are dendritic; as Vix noted, you run dynamic routing protocols in the center where there are multiple paths, and on hosts on the leaf nets you point default at the first router in the direction of the core and then forget about it (simple arrangements like this tend not to break and mess up your day). Maybe if you're feeling generous you rip a default route into the leaf nets so that if someone gets a new machine that's running evil routed and doesn't know about default routes and such they won't lose. On the other hand, maybe you would consider such a move to be anti-Darwinian and encouraging sloped-forehead, knuckle-dragging behavior.

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The border router does aggregation outbound and points the aggregates at Null 0 with a high metric.

True.

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This is for cases in which there is no other router participating within the customer iBGP mesh, and where there are N (N>=1) upstream providers, and where dynamic routing must take place within the ISP's routing domain for various reasons (portable dialup links, links that are time-sensitive, etc.)

The assumption in this case is a common egress point.

What percentage of the Internet's end-user customers have a single egress point for their networks? At a guess, I'd say 95%. If taking the preemptive step of installing pull-ups for those networks could reduce route flap by 75%, I submit that doing so expeditiously would get out of the woods at least for the time being. This is one of those cases in which the 90% solution is indeed the Right Thing. No, it won't scale if every end-user decides to become multihomed, but I don't see any great rush in that direction and compared to getting custom hacks put into the router code, it is very cost- and-effort-effective. If space to hold the statics in the configuration memory of the routers is an issue, you don't even have to do that -- a PC running BSDI with a trivially- hacked gated and connected to the fddi ring or "utility ethernet" in your POP can dynamically broadcast the pull-ups into your routers via rip or ospf, and would probably be easier to maintain and blow automatically-generated configs into than loading up the statics directly on the routers (at least you'd only have to do it once per POP instead of once per router). ---Rob Robert E. Seastrom -- rs@digex.net Network Engineer, Digex International My posting, my opinions, not speaking for the company, etc. etc.