ospf neighbourship DR

[SJ K]

Hi all

Switch1#show ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.0         128   FULL/BDR        00:00:36    192.168.254.25  GigabitEthernet1/0/4
1.1.1.0         128   FULL/BDR        00:00:36    192.168.254.18  GigabitEthernet2/0/12
1.1.1.0         128   FULL/DR         00:00:36    192.168.254.1   GigabitEthernet1/0/24

Current switch1 router-id = 1.1.1.1

Neighbor router-id = 1.1.1.0 / default priority is 128

Any idea why the 1st/2nd entry current router 1.1.1.1 is a DR and 3rd entry - current router 1.1.1.1 is a BDR ?

3rd entry is a /30 link though

Thank you

[Georg Pauwen · Accepted solution]

Hello,

I somewhere recall that if the OSPF priority is the same on all routers (1, if you haven't changed it manually) and the router IDs are identical, the first router to come online becomes the DR.

You could test that by bringing up the third router (which is now the DR) last...

[SJ K]

Hi George

Thanks for your reply

Neighbor router 1.1.1.0 priority is 128

How do i see the current switch 1.1.1.1 priority ? - if it is default 1 , then why is it the DR for the 1st / 2nd entry ?

Switch1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.0 128 FULL/BDR 00:00:36 192.168.254.25 GigabitEthernet1/0/4
1.1.1.0 128 FULL/BDR 00:00:36 192.168.254.18 GigabitEthernet2/0/12
1.1.1.0 128 FULL/DR 00:00:36 192.168.254.1 GigabitEthernet1/0/24

Thank you

[Georg Pauwen]

Hello,

the priority seems to be 128 for all three routers. If what I said applies, the third router came online first. As suggested, test if that actually works by e.g. bringing the third router online last...

[SJ K]

Hi George

There are only 2 routers

1.1.1.0 with priority 128 and 1.1.1.1 with default priority

They are connected by 3 links

Not sure why 1.1.1.1 is DR for the 1st/2nd entry since 1.1.1.0 has a higher priority

Thank you

[paul driver · Accepted solution]

Hello

Isn't necessary the case the higher rid, The router that's powers up before any other and starts ospf will promote itself to be the DR irrespective if it has RID priority lower than the rest

Once a DR has been elected, It cannot be substituted by another router with even an higher opsf priority ..etc, This can only be changed by manually forcing the clearing of the opsf process (clear ip ospf process), or a reload or the interface disconnects so try these examples of clearing the ospf process and post the results.

[SJ K]

Hi Paul

George and you are right - after i do a shut no shut on the interfaces - R1.1.1.1 is the BDR for all 3 links

Thank you