At 2:05 AM -0500 2/8/02, Mannan Venkatesan wrote:
>Guys,
>Sorry for the off-topic. I am doing an OSPF network design review and trying
>to document the resources used by OSPF (link bandwidth and router
CPU/memory).
>I have already gone through RFC 1245. Just wondering whether there is any
more
>good reference/documents regarding this.
>
>Thanks,
>Mannan
I'm copying this to the general list because it doesn't pertain
specifically to the CCIE lab, and some people on the lab list are
very sensitive to posts perceived to be off-topic.
First, the current OSPF specification is RFC 2328.
There is no simple answer, but let me give some ideas. LSAs are
variable length, but typically take up 200-400 bytes of memory each.
LSAs, of course, need to be preceded by packet headers, and there are
only so many LSAs that can fit into a packet.
How much bandwidth is consumed largely depends on how many LSAs are
in the area and how often they change. You could be conservative and
assume there will be a burst of all of them every 30 minutes,
although newer IOS implementations will spread that out over time. In
addition to this, you have variable-length HELLOs at a default
interval of 10 seconds.
To get an idea of CPU load, start with a single area. The CPU
loading for the route computation is proportional
(numberOfPrefixes**2)*log(numberOfRouters)
As you start introducing inter-area and external rates, they cause
the load generally to go up in a linear fashion, where the intra-area
computation (the true Dijkstra) increases the load exponentially.
The actual processor load, of course, will depend on how fast the
processor is. You could, I suppose, create a synthetic load and
measure the route table computation percentage of CPU (it should take
<1 second) and extrapolate that to the number of prefixes and routers
you expect to use.
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