Configuring System MTU

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

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Restrictions for System MTU

When configuring the system MTU values, follow these guidelines:

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

Information about the MTU

The default maximum transmission unit (MTU) size for frames received and transmitted on all interfaces is 1500 bytes. You can increase the MTU size for all interfaces operating at 10 or 100 Mb/s by using the system mtu global configuration command. You can increase the MTU size to support jumbo frames on all Gigabit Ethernet interfaces by using the system mtu jumbo global configuration command.

Gigabit Ethernet ports are not affected by the system mtu command; 10/100 ports are not affected by the system mtu jumbo command. If you do not configure the system mtu jumbo command, the setting of the system mtu command applies to all Gigabit Ethernet interfaces.

System MTU Values

The following MTU values can be configured:

    How to Configure MTU

    Configuring the System MTU

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

    SUMMARY STEPS

    1. enable
    2. configure terminal
    3. system mtu bytes
    4. system mtu jumbo bytes
    5. end
    6. copy running-config startup-config
    7. show system mtu

    DETAILED STEPS

      Command or Action Purpose
    Step 1

    enable

    Example:

    
Switch> enable

    Enables privileged EXEC mode.

    • Enter your password if prompted.

    Step 2

    configure terminal

    Example:

    Switch# configure terminal

    Enters global configuration mode.

    Step 3

    system mtu bytes

    Example:

    Switch(config)# system mtu 1900

    (Optional) Changes the MTU size for all Fast Ethernet interfaces.

    The range is 1500 to 1998 bytes; the default is 1500 bytes.

    Step 4

    system mtu jumbo bytes

    Example:

    Switch(config)# system mtu jumbo 7500

    (Optional) Changes the MTU size for all Gigabit Ethernet and 10-Gigabit Ethernet interfaces.The range is 1500 to 9000 bytes; the default is 1500 bytes.

    Step 5

    end

    Example:

    Switch(config)#  end

    Returns to privileged EXEC mode.

    Step 6

    copy running-config startup-config

    Example:

    Switch# copy running-config startup-config

    Saves your entries in the configuration file.

    Step 7

    show system mtu

    Example:

    Switch# show system mtu

    Verifies your settings.

    Configuration Examples for System MTU

    This example shows how to set the maximum packet size for a Gigabit Ethernet port to 7500 bytes: 

    
Switch(config)# system mtu 7500
Switch(config)# system mtu jumbo 7500
Switch(config)# exit

    If you enter a value that is outside the allowed range for the specific type of interface, the value is not accepted. This example shows the response when you try to set Gigabit Ethernet interfaces to an out-of-range number:

    Additional References for System MTU

    Error Message Decoder

    Description Link

    To help you research and resolve system error messages in this release, use the Error Message Decoder tool.

    https://www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi

    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

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    http://www.cisco.com/support