OSPF multi-level hierarchy: Necessary at all?

Alex Zinin zinin at amt.ru
Fri May 28 10:38:54 UTC 1999

At 15:33 27.05.99 -0700, Vadim Antonov wrote:
>Tony Li <tony1 at home.net> wrote:
>>I suspect that the main driver is not the amount of routing information
>>in the gross sense, but the scalability of the protocol as the number of
>>nodes increases.
>There's a better solution: decrease the number of nodes by replacing
>clusters with bigger boxes.  This has an additional advantage of reducing
>number of hops (and, consequently, latency variance).

"Have more bigger boxes rather than less smaller ones"-approach is not
for everybody and not for every case. If you have clusters sitting in one room,
powered from the same source, sharing the same ceiling that can fall, running 
the same version of soft, using the same config., etc., than yes it's ok, 
because they will more likely crash at the same moment. Otherwise, I'd think
first. Also, even if you do use a large box, you probably don't wanna know
all the details about it's connections at some level of your network.

>PS. Using DUAL or DASM instead of SPF helps, too -- these algorithms tend
>    to eliminate updates which "do not matter" unlike SPF-based algorithms
>    which have to inform everyone about local topology changes.

In SPF-based protocols we have areas for this purpose---we do not propogate
topology information across the area boundaries.
Also, magically we don't have SIAs in SPF even when there's a lot of traffic :)
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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