You can configure the MTU size for all interfaces on a device at the same time using the system mtu command. The default maximum transmission unit (MTU) size for frames received and transmitted on all interfaces is 1500 bytes.
The system mtu command is a global command and does not allow MTU to be configured at a port level. Starting with Cisco IOS XE 17.1.1, you
can configure Per-Port MTU. Per-Port MTU will support port level and port channel level MTU configuration. With Per-Port MTU
you can set different MTU values for different interfaces as well as different port channel interfaces.
Per-port MTU can be configured in the range of 1500-9216 bytes.
Once the Per-Port MTU value has been configured on a port, the protocol-specific MTU for that port is also changed to the
Per-Port MTU value. When Per-Port MTU is configured on a port, you can still configure protocol-specific MTU on the interface
in the range from 256 to Per-Port MTU value.
If the Per-Port MTU is disabled, the MTU for the port will revert to the system MTU value.
You can view the Per-Port MTU configurations on an interface using the show interface mtu command.
The following are expected behaviour if the Per-Port MTU configuration is changed on any interface:
The interface flaps if the port-channel is in PAgP or LACP mode.
The interface does not flap if the port channel is in the on mode.
The interface does not flap if the interface is not a port channel.
You can disable Per-Port MTU by using the no form of the mtubytes command in the interface configuration mode.