OSPF DR and BDR elections

Humper

OK! I am slightly confused with DR and BDR elections

I have configured 3 routers, all on ethernet interfaces. RouterA connects to RouterB via f0/0 on both Routers. They are configured 10.0.0.1 & 10.0.0.2 . Now RouterB is connected (f0/1) to RouterC (f0/1) as 10.0.1.1 and 10.0.1.2 . They have all been added to ospf, and area 0. All the default timers and priorities are the same. Now! Onto the election process, according to Tom's book it says that the DR is elected by the highest priority, and if the priority is the same the highest RouterID will be used. The RouterID is determined by the highest IP address on any interface, and a loopback can be used to override that. I dont have any loopback interfaces set. Now here is some output:

Router#show ip ospf interface

FastEthernet0/1 is up, line protocol is up
  Internet Address 10.0.1.1/24, Area 0
  Process ID 2, Router ID 10.0.1.1, Network Type BROADCAST, Cost: 64
  Transmit Delay is 1 sec, State DROTHER, Priority 1
  Designated Router (ID) 10.0.0.1 , Interface address 10.0.0.1
  Backup Designated router (ID) 10.0.1.2 , Interface address 10.0.1.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:08
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 0, maximum is 0
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 2, Adjacent neighbor count is 2
    Adjacent with neighbor 10.0.0.1(Designated Router)
    Adjacent with neighbor 10.0.1.2(Designated Router)
  Suppress hello for 0 neighbor(s)
FastEthernet0/0 is up, line protocol is up
  Internet Address 10.0.0.2/24, Area 0
  Process ID 2, Router ID 10.0.1.1, Network Type BROADCAST, Cost: 64
  Transmit Delay is 1 sec, State DROTHER, Priority 1
  Designated Router (ID) 10.0.0.1 , Interface address 10.0.0.1
  Backup Designated router (ID) 10.0.1.2 , Interface address 10.0.1.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:08
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 0, maximum is 0
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 2, Adjacent neighbor count is 2
    Adjacent with neighbor 10.0.0.1(Designated Router)
    Adjacent with neighbor 10.0.1.2(Designated Router)
  Suppress hello for 0 neighbor(s)

If the priorities are the same, and the highest IP address is 10.0.1.2 then why isn't it the DR and another interface the BDR? Is there something I am missing?

Thanks![/b]

keenon

just a thought.

and a question.


it looks as if 1 router came up before the others. so routers that come up later would fall into other ospf states ( as ospf doesn't preempt )
someone correct me if i'm wrong

so the question would be which router came up first?
then have you reset all the routers and let the ospf election restart

Humper

OK I think thats what It is because 10.0.0.1 is the first one i configured...let me try shutting down all the interfaces and then bringing them back up

Humper

Yea that fixed it! Thank you!

keenon

lwwarner

ModemHumper wrote:

OK I think thats what It is because 10.0.0.1 is the first one i configured...let me try shutting down all the interfaces and then bringing them back up

Or you can:

Router#clear ip ospf process

This will drop and rebuild all ospf adjacencies forcing a new dr/bdr election.

--Bill

duncnz

While on the same subject, if you change the IP address of the interface that was used for the process ID, how do your get the process ID to update?

lwwarner

duncnz wrote:

While on the same subject, if you change the IP address of the interface that was used for the process ID, how do your get the process ID to update?

Assuming you you really mean the router ID; already answered, see above. The process ID is set in your config:

R3(config)#router ospf ?
  <1-65535>  Process ID

--Bill

duncnz

lwwarner wrote:

duncnz wrote:

While on the same subject, if you change the IP address of the interface that was used for the process ID, how do your get the process ID to update?

Assuming you you really mean the router ID; already answered, see above. The process ID is set in your config:

R3(config)#router ospf ?
  <1-65535>  Process ID

--Bill

Sorry, yeah, I meant the router ID. I did try both the Router#clear ip ospf process and shutting down the interfaces, no joy with either. Am I missing something? Do I need to do a reload?

Thanks for your help.

lwwarner

Hmm, I thought that would have done it, but you're right, it doesn't. So, I guess it's either reload or set the router ID manually and then clear the ospf process:

R2(config)router ospf 1
R2(config-router)#router-id ?
  A.B.C.D  OSPF router-id in IP address format

R2(config-router)#router-id 9.9.9.9
Reload or use "clear ip ospf process" command, for this to take effect
R2(config-router)#^Z
R2#clear ip ospf proc
Reset ALL OSPF processes? [no]: y
R2#sh ip ospf
 Routing Process "ospf 1" with ID 9.9.9.9