Template:MTU/Debian

While the /etc/rc.local way is almost always guaranteed work in Debian, Debian won't absolutely guarantee the network is up before init reaches rc.local, so it's best to use /etc/network/interfaces instead.

If you're using DHCP:

auto eth0
iface eth0 inet dhcp
post-up /sbin/ip link set eth0 mtu [nnnn]

If you're using static addressing:

auto eth0
iface eth0 inet static
  address 192.168.1.nnn
  network 192.168.1.0
  netmask 255.255.255.0
  gateway 192.168.1.1
  broadcast 192.168.1.255
  mtu nnnn