Setting network speed in linux , ifconfig media, ethtool

For a "secured university network" we had to make sure that before we connected a computer to the network the network card needed to be "set to 100 FULL DUPLEX "

Otherwise it could block the port and we would have to call the networks team again.

This isn't hard but we were pulling our hair out for hours.

ethtool -s eth0 speed 100 duplex full

but before this works you NEED to turn off auto negotiations

ethtool -s eth0 autoneg off

If you don't turn off the auto negotiation the command seems about as useful as:

ifconfig media 100baseT