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