Configuring System MTU

Information About the MTU

The default maximum transmission unit (MTU) size for payload received in Ethernet frame and sent on all device interfaces is 1500 bytes. The maximum value of System MTU is 9216 bytes.

System MTU Value Application

This table shows how the MTU values are applied.

Table 1. MTU Values

Configuration

system mtu command

Standalone switch

You can enter the system mtu command on a switch and it affects all ports on the switch.

The range is from 1500 to 9216 bytes.

For more information about setting the MTU sizes, see the system mtu global configuration command in the command reference for this release.

Beginning from Cisco IOS XE Amsterdam 17.3.x, the minimum IPv6 system MTU is fixed at 1280 as per RFC 8200.

How to Configure MTU

The following tasks describe how you can configure MTU.

Configuring the System MTU

Follow these steps to change the MTU size for switched packets:

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

system mtu bytes

Example:

Device(config)# system mtu 1900

(Optional) Changes the MTU size for all interfaces.

Step 4

end

Example:

Device(config)# end

Enters global configuration mode, and returns to privileged EXEC mode.

Step 5

copy running-config startup-config

Example:

Device# copy running-config startup-config

Saves your entries in the configuration file.

Step 6

show system mtu

Example:

Device# show system mtu

Verifies your settings.

Configuring Protocol-Specific MTU

To override system MTU values on routed interfaces, configure protocol-specific MTU under each routed interface. To change the MTU size for routed ports, perform this procedure.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 2

interface interface

Example:

Device(config)# interface gigabitethernet0/0

Enters interface configuration mode.

Step 3

ip mtu bytes

Example:

Device(config-if)# ip mtu 68

Changes the IPv4 MTU size

Step 4

ipv6 mtu bytes

Example:

Device(config-if)# ipv6 mtu 1280

(Optional) Changes the IPv6 MTU size.

Step 5

end

Example:

Device(config-if)# end

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

Step 6

copy running-config startup-config

Example:

Device# copy running-config startup-config

Saves your entries in the configuration file.

Step 7

show system mtu

Example:

Device# show system mtu

Verifies your settings.

Configuration Examples for System MTU

Example: Configuring Protocol-Specific MTU

This example shows how you can configure protocol-specific MTU:

Device# configure terminal
Device(config)# interface gigabitethernet 0/1
Device(config-if)# ip mtu 900 
Device(config-if)# ipv6 mtu 1286
Device(config-if)# end

Example: Configuring the System MTU

This example shows how you can configure the system MTU:

Device# configure terminal
Device(config)# system mtu 1600
Device(config)# exit

Additional References for System MTU

Related Documents

Related Topic Document Title

For complete syntax and usage information for the commands used in this chapter.

See the Interface and Hardware Commands section in the Command Reference (Catalyst 9400 Series Switches)

Standards and RFCs

Standard/RFC Title
RFC 8200

Internet Protocol, Version 6 (IPv6) Specification

Feature History for System 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 Everest 16.6.1

System MTU

System MTU defines the maximum transmission unit size for frames transmitted on all interfaces of a switch.

Cisco IOS XE Cupertino 17.7.1

System MTU

This feature was implemented on supervisor modules C9400X-SUP-2 and C9400X-SUP-2XL.

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