Configuring System MTU

Configuring System MTU

This module describes how to configure the Maximum Transmission Unit for a system on Catalyst 3650 Series Switches and Catalyst 3850 Series Switches.

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 sent on all switch interfaces is 1500 bytes.

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 affects all the ports on the switch.

System MTU Value Application

In a switch stack, the MTU values applied to member switches depends upon the stack configuration. The following stack configurations are supported:

The upper limit of the IP or IPv6 MTU value is based on the switch or switch stack configuration and refers to the currently applied system MTU or the system jumbo MTU value. For more information about setting the MTU sizes, see the system mtu global configuration command in the command reference for this release.

Configuring the System MTU

Configuring the System MTU

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. system mtu bytes
  4. exit
  5. 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 1600
Applies the Maximum Transmission Unit (MTU) size for all Ethernet interfaces on the switch or the switch stack.
  • The MTU range is from 1500 to 9198. The default is 1500.
Step 4

exit

Example:

Switch(config)# exit

Exits global configuration mode and returns to privileged EXEC mode.

Step 5

show system mtu

Example:

Switch# show system mtu

Displays the configured global MTU size.

Configuring Protocol-Specific MTU

When system MTU changes, the range for the ip mtu command for interface also changes.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. ip mtu bytes
  5. ipv6 mtu bytes
  6. end
  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

interface type number

Example:

Switch(config)# interface gigabitethernet 0/0

Configures an interface and enters interface configuration mode.

Step 4

ip mtu bytes

Example:

Switch(config-if)# ip mtu 900 
Sets the maximum transmission unit (MTU) size of IP packets sent on an interface.
  • The range is from 832 to 1500.

Step 5

ipv6 mtu bytes

Example:

Switch(config-if)# ipv6 mtu 1300 
Set the MTU size of IPv6 packets sent on an interface.
  • The range is from 1280 to 1500.
Step 6

end

Example:

Switch(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 7

show system mtu

Example:

Switch# show system mtu

Displays the configured global MTU size.

Configuration Examples for System MTU

Example: Configuring the System MTU

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

Example: Configuring Protocol-Specific MTU

Switch# configure terminal
Switch(config)# interface gigabitethernet 0/0
Switch(config-if)# ip mtu 900 
Switch(config-if)# ipv6 mtu 1286
Switch(config-if)# end

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 XE 3.2SECisco IOS XE 3.2SECisco IOS XE 3.3SE

This feature was introduced.