When you have the “Mismatched OSPF Network Types” issue in Cisco switches, you may encounter log messages indicating the problem. These log messages can provide valuable information to help diagnose the issue. Here are some example log messages you might see in the Cisco switch logs:

  1. Message: %OSPF-4-ERRRCV: Received invalid packet: mismatched area ID from <Neighbor IP> on interface <Interface> Explanation: This log message indicates that the OSPF router received an invalid OSPF packet due to a mismatched area ID with the neighbor router on the specified interface. The area ID must be the same for OSPF routers to form adjacencies.
  2. Message: %OSPF-5-ADJCHG: Process <Process ID>, Nbr <Neighbor IP> on <Interface> from LOADING to EXSTART, SeqNumberMismatch Explanation: This log message indicates that the OSPF neighbor adjacency on the specified interface is transitioning from LOADING to EXSTART state due to a sequence number mismatch. This can occur when OSPF routers have different OSPF network types, causing synchronization issues during adjacency formation.
  3. Message: %OSPF-5-ADJCHG: Process <Process ID>, Nbr <Neighbor IP> on <Interface> from EXCHANGE to DOWN, Neighbor Down: Too many retransmissions Explanation: This log message suggests that the OSPF neighbor adjacency on the specified interface is transitioning from EXCHANGE to DOWN state due to excessive retransmissions. The adjacency may fail to establish due to mismatched OSPF network types causing Hello packets to be ignored or lost.
  4. Message: %OSPF-4-ERRRCV: Received invalid packet: mismatched hello parameters from <Neighbor IP> on <Interface> Explanation: This log message indicates that the OSPF router received an invalid OSPF packet due to mismatched Hello parameters with the neighbor router on the specified interface. Hello parameters, including Hello Interval and Dead Interval, must be consistent for OSPF routers to form adjacencies.
  5. Message: %OSPF-4-ERRRCV: Received invalid packet: mismatched authentication from <Neighbor IP> on <Interface> Explanation: This log message suggests that the OSPF router received an invalid OSPF packet due to authentication mismatch with the neighbor router on the specified interface. OSPF routers must have the same authentication settings to establish neighbor adjacencies.

These log messages provide valuable insights into the potential “Mismatched OSPF Network Types” issue and help in identifying the root cause of OSPF adjacency problems. When troubleshooting OSPF neighbor issues, monitoring the switch logs can be instrumental in identifying and resolving the problem effectively.

Reason: When OSPF routers have mismatched network types, their Hello packets contain different parameters related to the network type, such as the Hello Interval and Dead Interval. As a result, routers do not recognize each other as neighbors, and adjacency formation fails.

Solution:

To fix the “Mismatched OSPF Network Types” issue, ensure that the OSPF network types are consistent across all OSPF-enabled interfaces. The correct network type depends on the type of connection between routers.

  1. Broadcast Network Type:

For Ethernet interfaces, use the broadcast network type.

Cisco IOS Command to configure OSPF with the broadcast network type:

Router(config)# interface <interface>
Router(config-if)# ip ospf network broadcast

  1. Point-to-Point Network Type:

For point-to-point connections, use the point-to-point network type.

Cisco IOS Command to configure OSPF with the point-to-point network type:

Router(config)# interface <interface>
Router(config-if)# ip ospf network point-to-point

  1. Non-Broadcast Multi-Access (NBMA) Network Type:

For Frame Relay or other NBMA connections, use the non-broadcast multi-access (NBMA) network type.

Cisco IOS Command to configure OSPF with the NBMA network type:

Router(config)# interface <interface>
Router(config-if)# ip ospf network non-broadcast

  1. Point-to-Multipoint Network Type:

For point-to-multipoint connections, use the point-to-multipoint network type.

Cisco IOS Command to configure OSPF with the point-to-multipoint network type

Router(config)# interface <interface>
Router(config-if)# ip ospf network point-to-multipoint

  1. Point-to-Multipoint Non-Broadcast Network Type:

For Frame Relay or other point-to-multipoint non-broadcast connections, use the point-to-multipoint non-broadcast network type.

Cisco IOS Command to configure OSPF with the point-to-multipoint non-broadcast network type:

Router(config)# interface <interface>
Router(config-if)# ip ospf network point-to-multipoint non-broadcast

Remember to replace <interface> with the actual interface name, such as “FastEthernet0/0” or “Serial0/0”.

By configuring OSPF with the correct network type on all interfaces, you ensure that OSPF routers can form neighbor adjacencies successfully, allowing for efficient routing information exchange within the OSPF domain.