PacketTracer 4.1 - Flaw with OSPF Priority?

r_durant

I used PacketTracer 4.1 to simulate the hands-on lab in the add-on of OSPF DR and BDR Elections from the Sybex 5th Ed.

It simulated 3 x 2500 routers connected via their e0 interfaces, what I tried was not part of what is in the lab, but I tried it just to see what would happen...

I used 1841 routers because PT doesn't have the 25xx series...

I Router3 (10.1.1.3/24) was the DR and had a priority of 1, Router2 (10.1.1.2/24) was a DROTHER with a priority of 1 and Router1 (10.1.1.1/2) was the BDR with a priority of 3.

I changed the priority of Router1 to 0, did a shut and no shut and saw the elections taking place, Router1 was then elected DR and Router2 was BDR....

I know setting the priority to 0, should restrict a Router from participating in the election and setting it's status to a DROTHER....Or, does the RID have some say in the election??

Here's the "sh ip ospf int" for Router1...

Ethernet0/0/0 is up, line protocol is up
Internet address is 10.1.1.1/24, Area 0
Process ID 1, Router ID 10.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 0
Designated Router (ID) 10.1.1.1, Interface address 10.1.1.1
Backup Designated Router (ID) 10.1.1.2, Interface address 10.1.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 10.1.1.2 (Backup Designated Router)
Adjacent with neighbor 10.1.1.3
Suppress hello for 0 neighbor(s)

Router2...

Ethernet0/0/0 is up, line protocol is up
Internet address is 10.1.1.2/24, Area 0
Process ID 2, Router ID 10.1.1.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 10.1.1.1, Interface address 10.1.1.1
Backup Designated Router (ID) 10.1.1.2, Interface address 10.1.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 10.1.1.1 (Designated Router)
Adjacent with neighbor 10.1.1.3
Suppress hello for 0 neighbor(s)

Router3...

Ethernet0/0/0 is up, line protocol is up
Internet address is 10.1.1.3/24, Area 0
Process ID 3, Router ID 10.1.1.3, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DROTHER, Priority 1
Designated Router (ID) 10.1.1.1, Interface address 10.1.1.1
Backup Designated Router (ID) 10.1.1.2, Interface address 10.1.1.2
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 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 10.1.1.1 (Designated Router)
Adjacent with neighbor 10.1.1.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)

dtlokee

No the RID has no say if the priority is 0. There are two things that could be going on here, First the simulator is bugged (likely) and second, OSPF does not support premption of the DR/BDR role so changing te priority after the neighbors have been formed and the DR has been elected may not cause them to be reset and new DR/BDR election.

r_durant

Well, I'm thinking it's buggy...becuz since then, I changed the priority on the DR (Router1) to 3, an election took place and then Router2 became the DR...the original DR then became the BDR.