At a one network site, ME60s are upgraded from V600R006C00SPC300 to V600R008C10SPC300 and then restarted. Before the upgrade, the OSPF status of all interfaces is Full. After the upgrade, some interfaces remain in the Exchange state and cannot establish a neighbor relationship with an ME60.
The status of the corresponding interface remains in the Exchange state and cannot be changed to Full.
1. Ping the device to check the link status. The ping succeeds. Therefore, the interface connectivity on the ME60s after the upgrade is normal.
2. Compare the configurations of the device interfaces at both ends. It is found that the OSPF configurations, such as the MTU, addresses, OSPF authentication, and network advertisement address, are consistent.
3. Run the disp ospf error command. It is found that 135 errors with the type of Unknown neighbor exist.
4. Delete the OSPF authentication information from interfaces at both ends and then reconfigure the OSPF authentication. The problem persists.
5. Enable the debugging function on the ME60s and collect OSPF information. It is found that the corresponding interface receives information from the target device. The MTU value is 1548, indicating that OSPF packet exchanges have reached the LSA-U stage.
6. Based on the preceding information and the OSPF packet exchange process, if the link status is normal, the problem may arise from incorrect OSPF configurations. Because the authentication information has been modified, delete the MTU from the ME60 interfaces. After that, the OSPF status of the corresponding interfaces is changed to Full and the OSPF neighbor relationship can be properly set up.
Based on the OSPF error analysis and debugging analysis, Hello packets have been exchanged to set up OSPF neighbor relationships, and the OSPF neighbor status is changed as follows: init -> 2-way -> Exstart -> Exchange. .In the Exchange state, when routers exchange DD packets containing the link status information, negotiation fails between the two ends. As a result, the OSPF neighbor relationship fails to be set up. Packet discarding occurs because the receive end cannot process the DD packets received from the transmit end during DD packet exchanging. In addition, the ME60s are on the live network and therefore involves exchanges of lots of DD packets. When the local ME60 interface sends data packets carrying the configured MTU, the peer device cannot properly receive the packets. Such packets are discarded. Therefore, the OSPF neighbor relationship fails to be set up.
Additionally, it is doubted that the actual MTU on the peer device is inconsistent with the configured MTU. When the default MTU is used to receive data, the data packets received from the local device are sent based on the configured MTU. The peer device cannot receive such packets and therefore the data packets are discarded.
Delete the MTU configuration from the local interface and configure the ME60s to send data packets with the default MTU settings.
After the OSPF peer status is changed to Exchange, put the focus on interfaces' MTU configuration and OSPF configuration. Modify the MTU and OSPF configuration as required and locate the root cause of the problem.