Configuring System MTU

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.

  • When you change the size of the system MTU, reload the device for the new MTU value to take effect.


Note

If Layer 2 Gigabit Ethernet interfaces are configured to accept frames greater than the 10/100 interfaces, jumbo frames received on a Layer 2 Gigabit Ethernet interface and sent on a Layer 2 10/100 interface are dropped.

How to Configure MTU

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:

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 2

system mtu bytes

Example:

Device(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 9198 bytes; the default is 1500 bytes.

Step 3

system mtu jumbo bytes

Example:

Device(config)# system mtu jumbo7500

(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 4

end

Example:

Device(config)#  end

Returns to privileged EXEC mode.

Step 5

copy running-config startup-config

Example:

Device# copy running-config startup-config

Saves your entries in the configuration file.

Step 6

show system mtu

Example:

Device# 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: 


Device(config)# system mtu 7500
Device(config)# exit

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


Device(config)# system mtu jumbo 7500
Device(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: 


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

Additional References for System MTU

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

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 Release 15.0(2)EX

This feature was introduced.