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OSPF Neighbor Relationship Between an NE80 and a Non-Huawei Router Is Interrupted at Intervals

Publication Date:  2012-07-27 Views:  104 Downloads:  0

Issue Description

A user debugs all information on a c_router. After an NE80 is connected to the c_router, the OSPF neighbor relationship between them is interrupted every two minutes. All neighbor relationships are interrupted at the same time and then recover. The OSPF state machine transitions from Full to Down.
The c_router displays that the number of retransmission attempts is too great, and the number counted by the retransmission counter keeps increasing. This causes the OSPF process to be reset.
The display ospf peer command is run on the NE80. The command output shows that OSPF processes have been reset but the log messages do not show the cause for this. 

Alarm Information


Handling Process

  Another Huawei router (running the same version as the NE80 runs) and an S6503 are connected to the NE80. OSPF is configured on each device. After the OSPF neighbor relationship is established, the OSPF neighbor status is correct.
2. After a check, ARP entries on the NE80 are correct.
3. The NE80 uses 2000-byte packets to ping the c_router. The ping is successful, and this indicates that the MTU for the link on the NE80 is correct.
4. Data exchanged between the NE80 and c_router and between the NE80 and the other Huawei router is mirrored and analyzed. It is found that the NE80 seldom responds to LSA Update packets sent by the c_router, but responds properly to the LSA Update packets sent by the other Huawei router. In addition, LSA Update packets sent by these two routers are different.
The c_router of a specified version has a limit on retransmission attempts. After 24 retransmissions, the c_router considers that a fault in the OSPF process occurs and therefore forcibly resets the OSPF process. This is why there is no response or error on the NE80.
The fault does not recur after the retransmission counter is shut down, but the number counted by the retransmission counter keeps increasing. This means that the route update process is faulty. Therefore, the NE80 and c_router are restarted at a proper time upon approval of the customer.
After the routers are restarted, the number counted by the retransmission timer does not increase. This means that the fault occurs because the c_router sends incorrect LAS Update packets. 

Root Cause

 The debugging function enabled on the c_router results in a change in the location from hardware to the CPU for processing data. This affects the interconnection.
2. ARP entry learning is incorrect. This causes OSPF LSAck packets to be sent incorrectly.
3. An incorrect MTU value is set, which causes OSPF packets to be sent incorrect.
3. The NE80 sends incorrect LSA Update packets. After receiving the packets, the S8500 cannot identify the packets and therefore cannot reply with LSAck packets.
5. OSPF mechanisms on the NE80 and the c_router are different.  


 A c_router of a specified version has a limit on the number of retransmission attempts. This means that a c_router resets the OSPF process after 24 retransmissions. If a Huawei device is connected to a c_router and the c_router resets the OSPF process, disable the limit on the retransmission attempts on the c_router by using the following command. If the problem persists, check the packet exchange (for example, whether or not lots of packets are dropped on the link) and the MTU values.limit retransmission non-dc disable (OSPF process view)