OSPF multi-level hierarchy: Necessary at all?


but the main question is whether there is a demand
for it or not.

I guess the answer is pretty much not. The amount of interior
routing information in a properly designed backbone is quite
small even if there is no two-layer abstraction.

If you do not use route-summarization on the area borders,
your're gonna have flat network from the routing info's point
of view, even though the topology info is abstracted. Flat
networks are very well known to be not scalable.

(Now, the
_exterior_ information is aplenty, but OSPF is useless for it

The new approach could incorporate aggregating externals
on level borders in addition to aggregating internal routing info.

If someone proposed simplifying and cleaning up OSPF i'd be
quite for it. Building a protocol allowing to get rid of
iBGP hack would also help :slight_smile:

In OSPFv6 an ASE-LSA can point to another LSA, which per D. Ferguson
can contain BGP path attributes.
The new approach (which could be intergrated in OSPF for IPv6 btw)
could use a technique analogous to this one.


Btw. Flat network...

Routers now have - 128 or 256 MB RAM, 300 - 400 Mhz CPU. I guess you can
built flat betwork with 5,000 routers withouth hard problems.

Through it's not the question. There is _already_ 2 levels; you can use
multi-zone OSPF (independent OSPF networks connected by _redistribute_).
The question was _is 2-level hierarchy enougph__?