OSPF multi-level hierarchy: Necessary at all?

Alex P. Rudnev alex at Relcom.EU.net
Mon May 31 10:04:50 UTC 1999

> I was talking about ISP network which mostly is leased-line based.
> It depends on link stability and router stability.  As I pointed out
> in my previous message, the more router and link a network has (i.e.
> the large scaled network), the large chance of having link flapping
> and router crashes (if you think in percentage sense), the more flooding,
> SPF calculation and LSDB update all routers in the network have to
> handle.  If there is a hierarchy, then only a portion of routers (not all 
> the routers) would need to handle flooding, SPF calculation and LSDB update.
You are 100% right - it's the classic. 

Through the initial question whas _does we need hierarchical multi-level 
SPF routing schema?_. And my opinion was _yes, but due to administration, 
but not  CPU/memory issues (yes, this is important too but it's 
importance is usially overestimated).

And no one from this list argued for this hierarchy at all.

> Also, the large the size of network (lots of routers and links), the
> bigger the LSDB and the higher complexity of SPF calculation. 
> 						--Jessica    

Aleksei Roudnev, Network Operations Center, Relcom, Moscow
(+7 095) 194-19-95 (Network Operations Center Hot Line),(+7 095) 230-41-41, N 13729 (pager)
(+7 095) 196-72-12 (Support), (+7 095) 194-33-28 (Fax)

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