OSPF multi-level hierarchy: Necessary at all?

Alex Zinin zinin at amt.ru
Fri May 28 10:26:27 UTC 1999

At 11:35 27.05.99 -0700, Vadim Antonov wrote:
>>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 :)

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.

Alex D. Zinin, Consultant
CCSI #98966
CCIE #4015
AMT Group / ISL 
Cisco Systems Gold Certified Partner
irc: //EFNET/#cisco, //irc.msn.com/#NetCisco [Ustas]

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