largest OSPF core

Mark Smith nanog at
Thu Sep 2 21:50:18 UTC 2010

On Thu, 02 Sep 2010 15:20:05 +0300
lorddoskias <lorddoskias at> wrote:

>   I'm just curious - what is the largest OSPF core (in terms of number 
> of routers) out there?

Presuming OSPF and IS-IS SPF costs are fairly similar, the following
page from "The complete IS-IS routing protocol" (really quite a good
book, a bit of a shame that there are occasional minor errors that
better technical editing would have picked up) shows that relatively
modern (although a number of years old now) routers can perform SPF
calcs on SPF databases with 10000 routers and 25000 links in less than
a second. From that, it would seem that areas / levels are obsolete for
most networks for the purposes of reducing SPF calculation time. Still
possibly useful for route aggregation, although if BGP is carrying
nearly all your routes, that may not be that useful either."IS-IS"&pg=PA481#v=onepage&q&f=false

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