Routing Updates Across the WAN

Unanswered Question
Jul 3rd, 2007

Hi,

I am wondering how much is the average BW utilizization when OSPF and EIGRP multicast routing updates are happening?

Regards,

Haitham

I have this problem too.
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rais Tue, 07/03/2007 - 06:50

This should be dierectly proportional to the number of routes in your updates.

For single-homed networks you can use default routes.

Thanks.

Edison Ortiz Tue, 07/03/2007 - 07:01

It depends on the size of your routing table, therefore - there isn't any average.

The answer depends also on the routing protocol and how many changes you perform in the network that would trigger the routing protocol to send updates.

With that say, you will not experience bandwidth degradation due to the use of any routing protocol out there.

haithamnofal Wed, 07/04/2007 - 05:48

So, assuming a big enterprise using OSPF; with the complete routing update which happens every 30 min, although it is compressed, do you think will there be a serious BW consumption with the updates being communicated from the HQ to the remote branch?

Regards,

Haitham

Edison Ortiz Wed, 07/04/2007 - 06:41

OSPF is a link-state-routing protocol, it won't send a complete routing table every 30 minutes

haithamnofal Wed, 07/04/2007 - 07:29

Hi,

True OSPF is a link-state protocol why it sends an immediate routing update as soon as there is a change in the network topology, however it also send a complete compressed routing update every 30 min. Please refer to" RFC 1245:

http://www.ietf.org/rfc/rfc1245.txt

Regards,

Haitham

Edison Ortiz Wed, 07/04/2007 - 07:35

Haitham,

I stand corrected, good info there. I remember reading something similar a few months back but it escaped me when I posted, I should've verified before posting, my apologies.

However, you can reduce the LSA Flooding:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hirp_c/ch15/1chospf.htm#wp1016201

I believe you have to measure the impact of the WAN Circuits based on the size of the routing table. If you have some kind of bandwidth monitoring device, check the amount of traffic OSPF consumes every 30 minutes and adjust your OSPF configuration accordingly.

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