Analysis on TCP/IP Fault Handling

Some faults are inevitable during the use of the network. So this time we will analyze the problem of TCP/IP faults. First, let's take a look at what the TCP/IP fault is, and then handle it again.

TCP/IP fault

TCP/IP faults usually result in abnormal packet forwarding, including:

◆ Packet forwarding fails. If the ping fails.

◆ Packet loss.

The general guiding ideology for locating such problems is to break down from big to small. The procedure is as follows.

Procedure

1. Determine whether the forwarding subsystem is faulty.

Check whether the forwarding subsystem receives and sends packets.

2. You can run the display interface command to view the number of packets sent and received by the interface. If the statistics are normal, the forwarding subsystem of the current node does not have a problem. You need to locate the problem of the next node in the same way along the forwarding path.

3. Determine the module.

Once a faulty node is found, such as a vro, You need to determine the module where the problem is located.

You can run the display ip statistics and debugging ip packet acl-number commands along the forwarding path to view statistics or debugging information.

Use the preceding two commands to check whether the packet is discarded at the IP layer and why, such as TTL and Checksum.

4. Confirm the specific reason

Check whether the route is correct. Run the display fib command to view the forwarding table and check whether the corresponding forwarding item exists. Whether the next hop and outgoing interface of the forwarding item are correct. If the forwarding item is incorrect, the problem occurs in the routing subsystem. For details, see NE80E/40E router troubleshooting IP routing.

If the problem is caused by TTL, check whether the routing loop is faulty. Execute the display ip statistics command to view the specific location of the routing loop, or use the tracert command to determine the location where the loop occurs.

To check whether the IP layer receives the message, run the "display ip statistics" command to view the "Input" section in the display information.

◆ If no message is received, the link layer may fail. Of course, packet loss may also occur in the IP-related features. check whether there are any special configurations, such as QoS.

◆ If the message has been received, check whether the number of messages sent is correct.) if the message is sent correctly, run the display interface command to check whether packet loss occurs at the link layer and physical layer.

TCP/IP Fault Handling summary:

In short, check the relevant statistics and debugging information according to the forwarding process to locate the module where the problem occurs.