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Error: OSPF:0 Lost Slave Neighbor 10.10.8.50 (10.10.8.30) due to flag mismatch (seq 31176 vs 31176), MS: 1, 1, I:1 repeating over and over on the console.

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Information

 
TitleError: OSPF:0 Lost Slave Neighbor 10.10.8.50 (10.10.8.30) due to flag mismatch (seq 31176 vs 31176), MS: 1, 1, I:1 repeating over and over on the console.
Symptoms

Error:

OSPF:0 Lost Slave Neighbor 10.10.8.50 (10.10.8.30) due to flag mismatch (seq 31176 vs 31176), MS: 1, 1, I:1

is repeating over and over on the console.

OSPF neighbors appear to be stuck in EXST state.

Environment
Software Release: N/A
Fixed in Version: N/A
Cause

Possible reasons may be due to a mis-match in the IP MTU between neighbors, packet loss, or high CPU condition.

Resolution

Following are a list of actions to take based on the cause:

1) MTU Mismatch
To verify the that the IP MTU size is matching on both neighbors, issue a sh ip int e x/y on the BigIron RX and verify it is the same IP MTU as its neighbor. If they do not match either change the IP MTU size to match on both OSPF neighbors or configure one of the OSPF neighbors to ignore the MTU using the command: ip ospf ignore-mtu.

By default, the Layer 3 Switch compares the MTU in an OSPF database description packet received from another OSPF router with the MTU on the Layer 3 Switch. The Layer 3 Switch allows formation of an adjacency with the other router only if the MTU in the other routers packet matches the MTU on the Layer 3 Switch. Configuring the ospf mtu-ignore command enables you to disable the comparison to allow OSPF adjacency formation even when the Layer 3 Switch and the other OSPF router have different MTU values. To disable the MTU comparison, enter the following command at the interface configuration level:

BigIron(config-if-e1000-1/2)# ip ospf mtu-ignore

You can also issue the command debug ip ospf events to verify the MTU's being used on both OSPF Routers. Note: If remotely accessing the device the debug output will need to be redirected to your remote session, to determine the session number issue the sh who command.

BigIron-RX# debug destination telnet 1
BigIron-RX#
debug ip ospf events


To change the IP mtu size on the BigIronRX prior to software release 2.2.01, set the command default-max-frame-size at the global level.
To change the IP mtu size on the BigIronRX using software release 2.2.01 or later, set the commands default-max-frame-size at the global level and the ip mtu at the interface level.

2) High CPU
Issue the command sh cpu lp to verify the cpu levels of the LPs in the system. If they are high, click see SLN924 for troubleshooting help. (i.e. search for "SLN924" in the Brocade Knowledge Base without quotes).

3) Packet Loss
Verify the interface counters to see if any errors are beinglogged on the interface.
Run a ping test that traverses the BigIron RX to see if any ping loss is being experienced. If so, please contact Brocade Support for further assistance.

Additional notes

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