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OSPF process id and DR selection

 
 
hscottk hscottk is offline
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Join Date: Dec 2009
Posts: 1
 
      12-07-2009
Hello,

I am studying for the CCNA and found an odd result in the lab for OSPF DR elections. I am using a 2621 and 2821 in the lab.

Since we are told that the OSPF process id is only locally significant, I randomly chose two different numbers for the two routers (1 and 2). What I found was that the router with the process id of 1 always became the DR even when it had a lower router id. I even setup a loopback interface on the other router with a much higher IP address and still I got this result:

Scott_Lab_Router1#sh ip ospf in
GigabitEthernet0/0.2 is up, line protocol is up
Internet Address 192.168.2.1/24, Area 0
Process ID 2, Router ID 199.199.199.199, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 192.168.3.10, Interface address 192.168.2.10
Backup Designated router (ID) 199.199.199.199, Interface address 192.168.2.1
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 192.168.3.10 (Designated Router)
Suppress hello for 0 neighbor(s)

The other router......

Scott_Lab_Router2#sh ip ospf int
FastEthernet0/0 is up, line protocol is up
Internet Address 192.168.2.10/24, Area 0
Process ID 1, Router ID 192.168.3.10, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 192.168.3.10, Interface address 192.168.2.10
Backup Designated router (ID) 199.199.199.199, Interface address 192.168.2.1
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 199.199.199.199 (Backup Designated Router)
Suppress hello for 0 neighbor(s)


As you can see, the priorities on both interfaces are 1, so that can't be the issue. And when I changed the process id from 1 to 2 on router 2 (so they were both the same) the correct DR elections came up (see below).

Scott_Lab_Router2(config)#no router ospf 1
Scott_Lab_Router2(config)#
*Mar 1 01:09:01.311: %OSPF-5-ADJCHG: Process 1, Nbr 199.199.199.199 on FastEthe
rnet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
Scott_Lab_Router2(config)#router ospf 2
Scott_Lab_Rout(config-router)#network 192.168.2.0 0.0.0.255 area 0
Scott_Lab_Rout(config-router)#
*Mar 1 01:09:19.235: %OSPF-5-ADJCHG: Process 2, Nbr 199.199.199.199 on FastEthe
rnet0/0 from LOADING to FULL, Loading Done
Scott_Lab_Rout(config-router)#network 192.168.3.0 0.0.0.255 area 0
Scott_Lab_Rout(config-router)#^Z
Scott_Lab_Router2#
*Mar 1 01:09:38.019: %SYS-5-CONFIG_I: Configured from console by console
Scott_Lab_Router2#sh ip ospf int
FastEthernet0/0 is up, line protocol is up
Internet Address 192.168.2.10/24, Area 0
Process ID 2, Router ID 192.168.3.10, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 199.199.199.199, Interface address 192.168.2.1
Backup Designated router (ID) 192.168.3.10, Interface address 192.168.2.10
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 199.199.199.199 (Designated Router)

Can someone tell me why this is? Nothing in the book talks about an OSPF process id overriding other configurations in the eleciton of a DR or BDR.

Your help would be greatly appreciated
Scott
 
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donjohnston donjohnston is offline
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Join Date: Jun 2008
Posts: 38
 
      12-28-2009
Sounds like a bug in the IOS to me.

I would file it away for now and continue.
 
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