Configuring System MTU

Information About the MTU

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

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. show system mtu

DETAILED STEPS

  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

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

Step 3

system mtu jumbo bytes

Example:

Device(config)# system mtu jumbo7500

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)# 
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: