OSPF: DR/BDR election

Unanswered Question
Jul 16th, 2007

I have two P2P links both running parellel from router rtrA=======rtrB. The second link (backup)always hangs in exchange state with too many retransmittions. I am fairly new to OSPF, i think this is because both links are fighting to be the BDR. Not sure what to do. Any suggestions appreciated.

I have this problem too.
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Richard Burts Mon, 07/16/2007 - 12:19

Chris

If the links are Point to Point then the issue is not fighting to be the BDR. On P2P links there is no election of DR or BDR in OSPF.

It might help to start with posting the config of both routers. Also it would be helpful if you post the output of show ip ospf interface.

To resolve this we may need to run some debugs, but lets start with the config and interface information and see if we can find some answer.

HTH

Rick

Chris Lane Mon, 07/16/2007 - 13:04

Here is a debug. rtrA has lo0=RTR ID and interface x.x.x.x/30 to rtrB Same for rtrB.

Here is a snippet of my debug.

20:39.940: OSPF: Send DBD to x.x.x.x on Vlan50 seq 0x13DA opt 0x52 flag 0x7 len 32

Jul 16 13:20:39.940: OSPF: First DBD and we are not SLAVE

Jul 16 13:20:40.141: OSPF: Rcv DBD from x.x.x.x on Vlan50 seq 0x13DA opt 0x52 flag 0x2 len 1172 mtu 1500 state EXSTART

Jul 16 13:20:40.141: OSPF: NBR Negotiation Done. We are the MASTER

Jul 16 13:20:39.940: OSPF: 2 Way Communication to x.x.x.x on Vlan 50 state 2WAY

priority for both links are default (1)

sorry if this isn't enough.

Richard Burts Mon, 07/16/2007 - 13:30

Chris

I am puzzled about a couple of things. Your original post described a problem of hanging in Exchange State with too many retransmissions. But this debug does not show that at all.

I am also puzzled about the interfaces. You described the interfaces as P2P but the debug contains information about activity on interface VLAN 50. A VLAN interface would be treated by OSPF as a broadcast interface and would go through the process of election of BDR and DR. Did you describe the interfaces as P2P because they are /30 have have only a single neighbor or are they truly P2P. Posting the output of show ip ospf interface would probably be the best way to resolve this question.

The debug output shows the neighbors going to 2WAY state. This is not necessarily a problem. I would suggest that you shut down the interface on one router, start the debug, no shut the interface, and let the debug run until the situation has stabilized. That should give us better information about the problem.

HTH

Rick

Chris Lane Mon, 07/16/2007 - 13:44

FastEthernet7/1 is up, line protocol is up

Internet Address x.x.x.x, Area 0

Process ID x Router ID x.x.x.x, Network Type BROADCAST, Cost: 100

Transmit Delay is 1 sec, State BDR, Priority 1

Designated Router (ID) x.x.x.x, Interface address x.x.x.x

Backup Designated router (ID) x.x.x.x, Interface address x.x.x.x

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

oob-resync timeout 40

Hello due in 00:00:00

Supports Link-local Signaling (LLS)

Cisco NSF helper support enabled

IETF NSF helper support enabled

Index 4/4, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 1, maximum is 44

Last flood scan time is 0 msec, maximum is 4 msec

Neighbor Count is 1, Adjacent neighbor count is 0

Suppress hello for 0 neighbor(s)

GigabitEthernet6/0 is up, line protocol is up

Internet Address x.x.x.x, Area 0

Process ID x.x.x.x, Router ID x.x.x.x, Network Type BROADCAST, Cost: 5

Transmit Delay is 1 sec, State BDR, Priority 1

Designated Router (ID) x.x.x.x, Interface address x.x.x.x

Backup Designated router (ID) x.x.x.x, Interface address x.x.x.x

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

oob-resync timeout 40

Hello due in 00:00:09

Supports Link-local Signaling (LLS)

Cisco NSF helper support enabled

IETF NSF helper support enabled

Index 2/2, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 40, maximum is 40

Last flood scan time is 0 msec, maximum is 4 msec

Neighbor Count is 1, Adjacent neighbor count is 1

Adjacent with neighbor x.x.x.x (Designated Router)

Suppress hello for 0 neighbor(s)

NOW::

FastEthernet7/1 is up, line protocol is up

Internet Address x.x.x.x, Area 0

Process ID x.x.x.x, Router ID x.x.x.x, Network Type BROADCAST, Cost: 100

Transmit Delay is 1 sec, State BDR, Priority 1

Designated Router (ID) x.x.x.x, Interface address x.x.x.x Backup Designated router (ID) x.x.x.x, Interface address x.x.x.x Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

oob-resync timeout 40

Hello due in 00:00:09

Supports Link-local Signaling (LLS)

Cisco NSF helper support enabled

IETF NSF helper support enabled

Index 4/4, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 1, maximum is 44

Last flood scan time is 0 msec, maximum is 4 msec

Neighbor Count is 1, Adjacent neighbor count is 0

Suppress hello for 0 neighbor(s)

x.x.x.x 1 EXCHANGE/DR 00:00:00 x.x.x.x FastEthernet7/1

And NOW i just recieved this:

%OSPF-5-ADJCHG: Process x.x.x.x, Nbr x.x.x.x on FastEthernet7/1 from EXCHANGE to DOWN, Neighbor Down: Dead timer expired

This is from my Core which has 2 P2P wireless links to a Cisco 3750, which i have access ports with vlans. The only reason i feel there is issue is due to logging adj. This causes my logs to fill with neighbor on F7/1 bouncing.

Chris Lane Mon, 07/16/2007 - 13:48

Jul 16 13:25:10.151: %OSPF-5-ADJCHG: Process x, Nbr x.x.x.x on Vlan50 from EXCHANGE to DOWN, Neighbor Down: Too many retransmissions

Jul 16 13:26:10.151: %OSPF-5-ADJCHG: Process x, Nbr x.x.x.x on Vlan50 from DOWN to DOWN, Neighbor Down: Ignore timer expired

Jul 16 13:28:52.811: %OSPF-5-ADJCHG: Process x Nbr x.x.x.x on Vlan50 from EXCHANGE to DOWN, Neighbor Down: Dead timer expired

This is why i stated retransmissions. This is on my 3750.

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