Persistently change the MTU of an network interface (Debian)

Objective

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

Background and Scenario

See Change the MTU of a network interface.

Method

If the interface has (or can be given) a static configuration in /etc/network/interfaces then its MTU can be persistently altered by adding an mtu option to the relevant iface stanza, for example:

auto eth0
iface eth0 inet static
	address 192.168.0.2
	netmask 255.255.255.0
	mtu 9000

This method does not work when using other configuration methods such as dhcp.

You can activate the new MTU can 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.

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