I have some Ubuntu 14.04 machines running in an Amazon VPC. When they start, they have an MTU of 9001, but this appears to cause some problems when communicating with other servers which have an MTU of 1500. When I use
ip link set dev eth0 mtu 1500 these problems go away.
The problem is I can't seem to hit upon the correct way to make this permanent.
/etc/network/interfaces.d/eth0.cfg looks like this
auto eth0 iface eth0 inet dhcp pre-up /sbin/ip link set dev eth0 mtu 1500
I've also tried adding
mtu 1500 to bottom of that stanza too.
If I reboot, the machine comes back up with an MTU of 1500.
So what's the correct way to do this?