OSPF multi-level hierarchy: Necessary at all?

Sean Donelan SEAN at SDG.DRA.COM
Fri May 28 08:01:16 UTC 1999

avg at 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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