Configuring Per-Port MTU

Restrictions for Per-Port MTU

  • Per-Port MTU cannot be configured on the management port.

  • Per-Port MTU cannot be configured on SVL links.

  • On the Cisco Catalyst 9500 Series Switches - High Performance models,, members of a port channel cannot be configured with Per-Port MTU, they derive their MTU from the port-channel MTU configuration.

    On the Cisco Catalyst 9500 Series Switches, you can configure per-port MTU on a port-channel interface, but cannot configure per-port MTU on the port-channel members.

  • Per-Port MTU is not supported on subinterfaces and port-channel subinterfaces.

Information About Per-Port MTU

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.

Configuring Per-Port MTU

Follow these steps to change the MTU size for switched packets on a particular port of an interface:

Procedure

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password, if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

interfacetypeswitch-number/slot-number/port-number

Example:

Device(config)# int FortyGigabitEthernet2/5/0/20

Configures the interface and enters interface configuration mode.

Step 4

mtubytes

Example:

Device(config-if)# mtu 6666

Configures the MTU size for a particular port on the interface.

Step 5

end

Example:

Device(config-if)# end

Exits interface configuration mode, and returns to privileged EXEC mode.

Example: Configuring Per-Port MTU

This example shows how to configure Per-Port MTU on an interface:

Device# configure terminal
Device(config)# interface FortyGigabitEthernet2/5/0/20
Device(config-if)# mtu 6666 
Device(config-if)# end

Example: Verifying Per-Port MTU

This example shows how to verify Per-Port MTU on an interface using the show interface mtu command: 

Device# show interface mtu

Port           Name               MTU         
Fo2/5/0/19                        1500        
Fo2/5/0/20                        6666        
Fo2/5/0/21      ixia_7_21         1500

Example: Disabling Per-Port MTU

This example shows how to disable Per-Port MTU on an interface:

Device# configure terminal
Device(config)# interface FortyGigabitEthernet2/5/0/20
Device(config-if)# no mtu 
Device(config-if)# end

Feature History for Per-Port MTU

This table provides release and related information for features explained in this module.

These features are available on all releases subsequent to the one they were introduced in, unless noted otherwise.

Release

Feature

Feature Information
Cisco IOS XE Amsterdam 17.1.1

Per-Port MTU

Per-Port MTU defines the maximum transmission unit size for frames received and transmitted on a particular port or port channel.

Support for this feature was introduced on all the models of the Cisco Catalyst 9500 Series Switches.

Use Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to https://cfnng.cisco.com/.