OSPF Adjacency

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May 5th, 2010
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Hi serniors,

I have Lan/Wan setup in my office with Cisco routers & switches. OSPF is running on serial as well as multiaccess network. Yesterday I noticed that 2 routers changed adjacency from FULL/DROTHER to 2WAY/DROTHER. Network is running fine without any outage and impact. Later I noticed that a switch is installed on both of these routers interface that changed the adjacency but switch ports are up and running. My question is

  • why routers changed the OSPF adjacency ?



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Reza Sharifi Wed, 05/05/2010 - 17:51
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Hi Thair,

Did you add another router connecting to you current 2 routers using the same subnet.

This usually happens when you have 3 or more routers on the same subnet, one route is Designated Router (DR) and one Backup Designated Router (BDR). All other routers have a two-way adjacency established. This is normal behavior for OSPF.




tahir1234 Wed, 05/05/2010 - 18:28
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Nothing was added in that particular network. In that particular network there are 8 routers on the multiaccess network and definately on some segments there are DR and on the other therer are BDR. Routers have FULL/DR and FULL/BDR adjacency on other ports but on a certain port (as i told before) , the adjacency was FULL/DROTHER that changed to 2WAY/DROTHER. My concern is that "WHAT caused this change?" Moreover when i see the router logs , it displays that adjacency changed from full to 2way & when i run "show cdp neighbor" on both routers , neither is in the cdp neighbor list while they are connected. No one changed the priority on the routers as well.



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