Force 100MB Full Duplex on Network interface

See current settings:
[root@lx root] /root> ethtool eth0
Settings for eth0:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Advertised auto-negotiation: Yes
Speed: 10Mb/s
Duplex: Half
Port: MII
PHYAD: 32
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: pumbg
Wake-on: p
Current message level: 0xffffffff (-1)
Link detected: yes

Change settings:
[root@lx root] /root> mii-tool -F 100basetx-fd

Check new settings applied:
[root@lx root] /root> ethtool eth0
Settings for eth0:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Advertised auto-negotiation: No
Speed: 100Mb/s
Duplex: Full
Port: MII
PHYAD: 32
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: pumbg
Wake-on: p
Current message level: 0xffffffff (-1)
Link detected: yes

If new settings have not been applied then restart the interface:
[root@lx root] /root> ifdown eth0
[root@lx root] /root> ifup eth0