Why does the MTU value change on the Huawei router fail?

MTU is the abbreviation of MaximumTransmissionUnit, which is the largest data packet transmitted over the network. MTU of most network devices is 1500, and MTU is measured in bytes. If the MTU of the local machine is larger than the MTU of the gateway, large data packets will be split and transmitted, which will produce a lot of data packet fragments, increase the packet loss rate and reduce the network speed.

Setting the MTU of the local machine to be smaller or the same as the MTU of the gateway can reduce packet loss. MTU refers to the maximum packet size that can be passed by a layer of a communication protocol, the maximum transmission unit is usually related to the communication interface.

I. Networking Environment

The router connects to the peer device through POS1/0/0 interfaces. When you use the mtu command to change the MTU value of the POS interface to 1500 bytes, it is found that the MTU value does not take effect.

Ii. Fault Analysis

1. In the POS interface view, run shutdown and undo shutdown to restart the POS interface.

2. Execute the display interface pos command and find that the valid MTU value is still 1492 bytes.

3. Check the peer device and find that the MTU value of the Peer POS interface is 1492 bytes. If the MTU values of the two ends are inconsistent during MRU negotiation, the negotiation result is based on one end with a small MTU value.

Iii. troubleshooting

Perform the following operations on the vro to change the MTU value of the Peer POS interface to 1500 bytes and restart the interface. After the configuration is complete, the MTU values at both ends are 1500 bytes. The fault is solved.

During MRU negotiation, if the MTU values at both ends of the PPP are inconsistent, the negotiation result will be accurate at one end with a small MTU value. This is the same as the setting of the BelKin router, and data packets must be split and sent. In this case, reduce the packet length and then execute the ping command above.

Try the packet length several times from 1400 to 1472. Add the packet length to the packet header by 28 bytes to obtain the MTU value.

If the MTU value of the gateway is 1500, no modification is required.

If the gateway cannot be pinged through a firewall, set MTU to 1400.