Configuring System MTU

Restrictions for System MTU

When configuring the system MTU values, follow these guidelines:

  • The device does not support the MTU on a per-interface basis.

  • If you enter the system mtu bytes command in global configuration mode, the command affects all the switched and routed ports on the switch.

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.

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 9198 bytes.

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

How to 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

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

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

Example: Configuring the System MTU

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

Additional References for System MTU

MIBs

MIB MIBs Link

All the supported MIBs for this release.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/support

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.

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