From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Tue Nov 04 2003 - 15:43:08 GMT-3
At 5:49 PM +0000 11/4/03, Nawaz, Ajaz wrote:
>surely the number of networks and links matters more than the number of
>routers.
>
>Is IS-IS the only real protocol if you have more
>> than 30 routers?
>
>IMHO that generally will depend on how well the network was designed and
>will it scale effectively...
>
>ajaz
In general, the computational workload for the single-area Dijkstra
part of the SPF algorithm is proportional to:
networks**2 * log(routers)
The rest of the SPF calculation increases linearily with the number
of inter-area routes, and then by the number of externals. This
computation is internal to the link state protocol, and does not
consider the additional overhead of the main routing table
installation task checking these new routes.
This calculation represents only one instance of recomputing the SPF
tree. Conceptually, whenever a link changes state, this computation
must be redone, so processor load increases as a function of link
reliability. To some extent, you can reduce this load, at the
potential cost of suboptimal routing, by increasing the spf holddown
timer. Of course, making areas smaller reduces the computational
load as well.
The guideline of not more than 3 areas per ABR simply is a practical
rule that tends to avoid the possibility of having to run the SPF
algorithm simultaneously in more than one area.
>
>---Original Message-----
>From: Clay Maney [mailto:clay@pronettech.com]
>Sent: 04 November 2003 17:28
>To: Robert N Myhre
>Cc: ccielab@groupstudy.com
>Subject: Re: OT: OSPF
>
>
>For what it's worth, I have personally worked on a 300 router
>network that was all EIGRP, and there didn't appear to be any
>problems with it.
>
>It was in place long before I got there and they just needed
>some new stuff added to the net... as far as I know, it's still
>running (this was about a year and a half ago).
>
>Clay
>
>On Tue, Nov 04, 2003 at 08:50:10AM -0600, Robert N Myhre wrote:
>> Hello,
>>
>> I am interested to find out your experience in what the largest
>> network (in terms of number of routers) that you have worked on/seen
>> that is running OSPF. Is IS-IS the only real protocol if you have more
>> than 30 routers?
>>
>> Robert
>>
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