Configuring System MTU

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Information about the MTU

The default maximum transmission unit (MTU) size for frames received and sent on all switch interfaces is 1500 bytes. You can change the MTU size to support switched jumbo frames on all Gigabit Ethernet and 10-Gigabit Ethernet interfaces and to support routed frames on all routed ports.

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.

  • If you enter the system mtu bytes global configuration command, the command does not take effect on the switch. This command only affects the system MTU size on Fast Ethernet switch ports.

How to Configure MTU Sizes

Configuring the System MTU

Beginning in privileged EXEC mode, follow these steps to change the MTU size for switched and routed packets:

SUMMARY STEPS

    1.    configure terminal

    2.    system mtu bytes

    3.    system mtu jumbo bytes

    4.    system mtu routing bytes

    5.    end

    6.    copy running-config startup-config

    7.    reload

    8.    show system mtu


DETAILED STEPS
     Command or ActionPurpose
    Step 1configure terminal


    Example: 
    Switch# configure terminal
     

    Enters global configuration mode.

     
    Step 2system mtu bytes


    Example: 
    Switch(config)# system mtu 2500
     

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

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

     
    Step 3system mtu jumbo bytes


    Example: 
    Switch(config)# system mtu jumbo 7500
     

    (Optional) Changes the MTU size for all Gigabit Ethernet and 10-Gigabit Ethernet interfaces on the switch or the switch stack.

    The range is 1500 to 9198 bytes; the default is 1500 bytes.

     
    Step 4system mtu routing bytes


    Example: 
    Switch(config)# system mtu routing 2000
     

    (Optional) Changes the system MTU for routed ports. You can also set the maximum MTU to be advertised by the routing protocols that support the configured MTU size. The system routing MTU is the maximum MTU for routed packets and is also the maximum MTU that the switch advertises in routing updates for protocols such as OSPF.

    Note   

    This command is not supported on switches running the LAN base feature set.

     
    Step 5end


    Example: 
    Switch(config)#  end
     

    Returns to privileged EXEC mode.

     
    Step 6copy running-config startup-config


    Example: 
    Switch# copy running-config startup-config
     

    Saves your entries in the configuration file.

     
    Step 7reload


    Example: 
    Switch#  reload
     

    Reloads the operating system.

     
    Step 8show 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 1900
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: 

    Switch(config)# system mtu jumbo 25000
                                   ^
% Invalid input detected at '^' marker.

    This is an example of output from the show system mtu command: 

    Switch# show system mtu
Global Ethernet MTU is 1500 bytes.

    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 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 Information for System MTU

    Release

    Modification

    Cisco IOS 15.0(2)EX1

    This feature was introduced.