Configuring the MTU
Context
The size of data packets is limited at the network layer. Any time the network layer receives an IP packet to be sent, it checks to which local interface the packet needs to be sent and obtains the MTU configured on the interface. Then, the network layer compares the MTU with the packet length. If the packet length is greater than the MTU, the IP layer disassembles the packet to fragments, each not greater than the MTU.
- If the MTU is too small whereas the packet size is large, the packet is probably split into many fragments. Therefore, the packet may be discarded due to the insufficient QoS queue length.
- If the MTU is too large, packets are transmitted slowly or even lost.
Procedure
- Run system-view
The system view is displayed.
- Run interface pos interface-number
The POS interface view is displayed.
- Run mtu mtu
The MTU is configured for the POS interface.
By default, the MTU of a POS interface is 1500 bytes.
After changing the MTU on an interface using the mtu command, run the shutdown and undo shutdown/restart commands in the interface view to restart the interface for the configuration to take effect.
