Configuring System MTU

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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.


Note

The switch supports jumbo frames at CPU.

System MTU Guidelines

When configuring the system MTU values, follow these guidelines:

  • 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.

How to Configure MTU Sizes

Configuring the System MTU

Beginning in privileged EXEC mode, follow these steps to change the MTU size for all 10/100 or Gigabit Ethernet interfaces:

SUMMARY STEPS

    1.    configure terminal

    2.    system mtu bytes

    3.    system mtu jumbo bytes

    4.    end

    5.    copy running-config startup-config

    6.    reload

    7.    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) Change the MTU size for all interfaces on the switch stack that are operating at 10 or 100 Mb/s.

    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 interfaces on the switch or the switch stack.

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

     
    Step 4end


    Example: 
    Switch(config)#  end
     

    Returns to privileged EXEC mode.

     
    Step 5copy running-config startup-config


    Example: 
    Switch# copy running-config startup-config
     

    Saves your entries in the configuration file.

     
    Step 6reload


    Example: 
    Switch#  reload
     

    Reloads the operating system.

     
    Step 7show 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)EX

    This feature was introduced.