Hmm. THis is the right direction for this discussion - if someone built telephone network over IP technology (even if it's not public internet), he need quite scalable IGP protocol. Through you dont' need plain IGP schema - you have backbone (with 100 - 300 nodes) and regional access networks - every not too large. It can be build just as any ISP+customers. It's not so beautiful as multi-level scheme, but well designed and work just fine (OSPF+IBGP backbone, OSPF+iBGP customers). On Fri, 28 May 1999, Sean Donelan wrote:

Date: Fri, 28 May 1999 3:01:16 -0500 From: Sean Donelan <SEAN@SDG.DRA.COM> To: nanog@merit.edu Subject: Re: OSPF multi-level hierarchy: Necessary at all?

avg@kotovnik.COM (Vadim Antonov) writes:

...

Well, actually it is not that bad. The biggest number of locations is probably found in AT&T phone network - 250 or so. Sprint is in few dozen. The existing IGPs are quite happy with that kind of complexity, so if you belong to the "one-router-per-POP" school of thought the IGP complexity is a non-issue.

Well, the phone system is already hierarchial. The top-level is pretty small, it is the second and third levels which are monsters.

There are about 100,000 NXX's in the country. California has the largest state with about 12,000. The Los Angeles LATA is the biggest at about 5,000. Within PacBell there are about 800 CLLI locations for the Los Angeles LATA, not including all the other CLECs who may have locations in LA. Getting from the relatively few IXC access tandems to those 800 locations is the trick.

I may be doing something wrong, but I've found OSPF gets a bit cranky with far less than 800 routers and 5,000 routes in an area. -- Sean Donelan, Data Research Associates, Inc, St. Louis, MO Affiliation given for identification not representation

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