Configuring System MTU

Information About the MTU

The default maximum transmission unit (MTU) size for frames received and sent on all device 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 device does not support the MTU on a per-interface basis.

How to Configure MTU

Configuring the System MTU

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

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

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

Step 3

system mtu jumbo bytes

Example:

Device(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 4

system mtu routing bytes

Example:

Device(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 5

end

Example:

Device(config)#  end

Returns to privileged EXEC mode.

Step 6

copy running-config startup-config

Example:

Device# copy running-config startup-config

Saves your entries in the configuration file.

Step 7

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)EX1

This feature was introduced.