OSPF Link State Updates - how often in a stable netwrok

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Dec 27th, 2007
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Link State updates - how often should they occure. The text book says a link state update should occur only when a rotuer detects a missing piece in its database or when topology changes. This would mean to me then that in a stable network, link state updates should occure very infrequently. While playing with the "show ip traffic" command this morning I noticed one of the outputs to this was the following:

OSPF statistics:

Rcvd: 9279 total, 0 checksum errors

7306 hello, 37 database desc, 12 link state req

1003 link state updates, 921 link state acks


Sent: 4948 total

3662 hello, 44 database desc, 7 link state req

945 link state updates, 294 link state acks


I've noticed that the link state updates counter is increasing.


Does this mean routing instability of some sort in my network? As I check around my network I do not see routes coming and going so I'd like to understand what those mean and if they are normal in a stable network.

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Hi There


I'm not expert, just a CCNP candidate, but I

wonder if the increasing LSU counter is down to the fact that LSU's are used for the dispersal of LSA's and an OSPF router will transmit LSA's


1. When an adjacency is first formed

2. When there is a topology

3. Every 30 minutes whether a topology change

has occurred or not


So the fact the LSA's are sent every 30 minutes and LSU's carry the LSA(s), is this the cause of the increase you are seeing?


Just a possibility. Of course it will depend on how quickly the counter is incrementing and how many interfaces on the router are taking part in OSPF.



Best Regards,


Michael

shrikar.dange Thu, 12/27/2007 - 20:32
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hi,


I think michael is absolutely right.All the three reasons are responsible to trigger LSU.

In my opinion the increased LSA counter is due to the 30 mins LSA refresh timer causing to flood the LSUs.


Regards,

shri.

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