Persistently change the MTU of an network interface (Red Hat)

Objective

To persistently change the MTU of a network interface on a Red Hat-based system

Background and Scenario

See Change the MTU of a network interface.

Method

Edit the configuration script for the relevant interface in /etc/sysconfig/network-scripts/. If named directly after the interface eth0 then this would be called ifcfg-eth0, however other names are possible (including ifcfg-Auto_eth0 if using the Gnome Network Manager). If no configuration script exists then you will need to create one.

Add a line to specify the MTU, for example:

DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.168.0.2
NETMASK=255.255.255.0
MTU=9000

Unlike the corresponding method for Debian-based systems, it is possible to set the MTU of interfaces that use DHCP:

DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=02:00:00:00:00:00
ONBOOT=yes
MTU=9000

It is permissible for the values given in this file to be single- or double-quoted.

The new MTU can be activated by taking the interface down using ifdown then bringing it back up using ifup:

ifdown eth0
ifup eth0

Alternatively you could reboot the machine.

Testing

See Change the MTU of a network interface.

Errors

SIOCSIFMTU: Invalid argument

See Change the MTU of a network interface.

Invalid mtu value

An error of the form:

Error: argument "x" is wrong: invalid "mtu" value

indicates that the specified MTU could not be interpreted as an integer.

Alternatives

The following configuration programs have the ability to change the MTU of a network interface:

Distribution	Command	Menu item
Centos 5.5	system-config-network	System ⇒ Administration ⇒ Network
Fedora 14	nm-connection-editor	System ⇒ Preferences ⇒ Network Connections
OpenSUSE 11.3	yast2	Computer ⇒ YaST

These interoperate with the configuration script described above, so it should be possible to switch between manual and assisted configuration with caution.

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