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New Member

OSPF

Can someone tell me how to calculate the amount of bandwidth consumed by OSPF when sending LSAs and Hello Packets?

Thanks.....

2 REPLIES
Gold

Re: OSPF

Hello packets are small, so figure about 64 bytes per hello, by the rate at which the routers on the link are sending hello's. For LSA's, figure about 20 routes per LSA, I think, maybe 25, for a full 1500 byte packet, and then a 64 byte ack. So, I'd think you could probably come close by figuring the number of routes in the database, dividing by 20, and then multiply by (1500 + 64), or something like that. But, that would be for a full database....

At initial convergence, you're also going to exchange some number of DBD's. I'd think about 100 or so LSA ID's per DBD, so the same sort of calculation as above. For ongoing convergence, it's going to depend on the number of routes changing, how often they change, and how many LSA's you can get into a packet (which is partially based on the LSA origination and other timers in the network).

It's rather more complex than it looks at the outset--I'd say it's next to impossible to actually calculate in any reliable way.

Russ.W

New Member

Re: OSPF

Thank you...that was very helpful.

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