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Tuesday, October 26, 2010


Again working on the following OSPF lab and trying to figure out how does a router update and "erase" routes for neighbor routers?!
While summarize the networks from R4 (10.4.x.x) on the ABR (R3) i have done some packet capture in order to see the process of LSA update. I have run wireshark on the f0/0 interface, on R3, which connected to area 0 (SW1) and here are the results:

Before i have configured summarization on R3, he advertised 4 networks (,,, after configuring area 2 range, R3 which is the DR of area 0 has send two LSA updates to (AllSPFRouters), the first an LSA update with, take note for the LA age which is 1 and the metric which is 65

The second LSA update packet was with 4 LSA's, 1 identical to the update on the summary address and 3 more, one for each subnet. But this time pay attention to the LS age and metric...

Each subnet was advertised with LS age of 3600 seconds and a metric of 1677215, by that the ABR keeps that the no new request (LSR) regards these subnets will be sent and the metric, which is in it's maximum value, is 16777215 so no SPF calculation will choose this path.

Following these packet capture findings i assume that subnets 10.4.x.x should be placed on the OSPF database for at least 1 hour more (LS age 3600) but i can't find the show command to see them...

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