Re: OSPF multi-level hierarchy: Necessary at all?

["Alex P. Rudnev" <alex () Relcom EU net>]

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__?

On Fri, 28 May 1999, Alex Zinin wrote:

> Date: Fri, 28 May 1999 14:26:27 +0400
> From: Alex Zinin <zinin () amt ru>
> To: Vadim Antonov <avg () kotovnik com>, nanog () merit edu
> Subject: Re: OSPF multi-level hierarchy: Necessary at all?
>
>
> 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
> > anyway).
>
> 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.
>
> Rgds
> ------------------------------------------------------------------
> Alex D. Zinin, Consultant
> CCSI #98966
> CCIE #4015
> AMT Group / ISL 
> Cisco Systems Gold Certified Partner
> http://www.amt.ru
> irc: //EFNET/#cisco, //irc.msn.com/#NetCisco [Ustas]

Aleksei Roudnev, Network Operations Center, Relcom, Moscow
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