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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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The OSPF Neighbor Relationship Cannot Be Established Between Two Devices Because the Link Between the Devices Is Faulty

The OSPF Neighbor Relationship Cannot Be Established Between Two Devices Because the Link Between the Devices Is Faulty

Fault Symptom

In the networking shown in Figure 19-10, the OSPF neighbor relationship cannot be established between Router A and its neighbor, and the neighbor is in the Exchange state.

Figure 19-10 Network diagram of the networking where the neighbor relationship cannot be established between two devices

Fault Analysis

The possible causes are as follows:

  • The OSPF configurations are improper.
  • Parameters of the two devices are incorrectly set.
  • The OSPF packets are lost.

Check the configuration of Router A and find that Router A is correctly configured.

Check the OSPF parameters on the corresponding interfaces and find that the OSPF parameters on the interfaces are set correctly.

Run the related debugging command on Router B and find that MTU negotiation fails.

The MTUs on the two devices are 4470. The debugging ospf packet dd command, however, shows that the MTU contained in the packet received by Router B is 0, which indicates that the MTU is not set on the peer device. It is concluded that the link is not working normally.

Run the following command on Router A to ping the peer device. Packet loss occurs.

<RouterA> ping 10.1.1.0
  PING 10.1.1.0: 56  data bytes, press CTRL_C to break
    Request time out
    Reply from 10.1.1.0: bytes=56 Sequence=2 ttl=255 time=5 ms
    Reply from 10.1.1.0: bytes=56 Sequence=3 ttl=255 time=5 ms
    Reply from 10.1.1.0: bytes=56 Sequence=4 ttl=255 time=5 ms
    Request time out
 --- 10.1.1.0 ping statistics ---                                          
    5 packet(s) transmitted                                                     
    3 packet(s) received 
    40.00% packet loss

Ensure that the link between intermediate transmission devices is normal. Collect traffic statistics from Router A. It is found that packet loss does not occur on Router A. Therefore, packet loss may be occurring on the board of the peer device or on the link.

Collect traffic statistics on the peer device. It is found that packet loss occurs on the board on Router B because the board is faulty

Procedure

  1. Replace the faulty board on Router B.

Summary

Sometimes, OSPF packets are not received. In this case, check connectivity at the link layer first. Enable OSPF debugging with the commands such as the debugging ospf packet and debugging ospf event commands to locate the fault, or run the display ospf error command to view the various OSPF error statistics. If the OSPF configuration is correct, run the debugging ip packet command to check whether packets are successfully forwarded at the IP layer.

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Updated: 2019-08-09

Document ID: EDOC1000079719

Views: 490796

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