Huawei Router changes the MTU value failure reason

MTU is the abbreviation of Maximumtransmissionunit, is the largest packet of packets on the network, most network device MTU is 1500,MTU unit is byte, if the MTU of the machine than the MTU of the gateway, large packets will be removed from the transmission, This will result in a lot of packet fragmentation, increase the packet loss rate, reduce network speed.

By setting the MTU of this machine to be smaller or the same than the MTU of the gateway, the MTU refers to the maximum packet size that can be passed on a layer of a communication protocol, and the maximum transmission unit is usually associated with the communication interface.

First, networking environment

The router connects to the End-to-end device through the pos1/0/0 interface. When you use the MTU command to modify the MTU value of the Pos interface to 1500 bytes, it is found that the MTU value does not take effect.

Second, failure analysis

1, in the POS interface view, the implementation of shutdown and undo shutdown, restart the POS interface.

2, the implementation of display interface POS, found to be effective MTU value is still 1492 bytes.

3, check to the end of the device, found that the End-to-end POS interface MTU value of 1492 bytes, PPP in the MRU negotiation, if the MTU values at both ends of the configuration inconsistent, the results of the negotiations will be small MTU value of the end.

Third, the fault handling

On the router, the MTU value of the End-to-end POS interface is modified to 1500 bytes, the interface is restarted, and after the configuration is complete, the MTU value at both ends is 1500 bytes, which resolves the problem.

PPP in the MRU negotiation, if the MTU values are not configured at both ends, the negotiated result will be the same as the MTU value of the small, this is the same as the Belkin router settings, the packet needs to be removed to send. At this point, reduce the packet length, and then execute the ping command above.

Try a few more times from 1400 to 1472 to find the right packet length. The value of the MTU is obtained by adding a packet length of 28 bytes to the packet header.

If the MTU value for the gateway is detected to be 1500, no modification is required.

If the gateway has a firewall ping, try to set the MTU to 1400 directly.