Software Configuration Guide, Cisco IOS Release 15.2(2)E (Catalyst 2960, 2960-S, 2960-SF and 2960-Plus Switches)
Configuring System MTU
Downloads: This chapterpdf (PDF - 1.26MB) The complete bookPDF (PDF - 13.41MB) | The complete bookePub (ePub - 3.33MB) | Feedback

Configuring System MTU

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.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http:/​/​www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

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.

You cannot set the MTU size for an individual interface; you set it for all 10/100 or all Gigabit Ethernet interfaces. When you change the system or jumbo MTU size, you must reset the switch before the new configuration takes effect.

How to Configure MTU

Configuring the System MTU

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

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
     

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

     
    Step 3system mtu jumbo bytes


    Example:
    Switch(config)# system mtu jumbo 7500system mtu 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 9000 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)# 
    Switch(config)# 
    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:

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

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