PFSense - Network - Force Interface Speed or Duplex Settings

WARNING: When forcing a speed and/or duplex option, both sides must match.

You cannot force a speed on an unmanaged switch.

Having a speed/duplex mismatch will result in errors and/or degraded connectivity.

Errors will result in In/Out errors and Collisions on Status → Interfaces.

Force the speed of the network cards and set the Duplex mode

Navigate to Interfaces → LAN. This is the Physical Interface.

Speed and Duplex: Select the desired speed and duplex from the drop-down menu.
Click Save
Click Apply Changes.

Natigate to Status → Interfaces and check the Media line for the interface in question.

If the selected speed and duplex are listed, then the setting has been applied as expected.

To switch back to autoselect, use the same settings and select Default under Speed and Duplex.

NOTE: Some network cards do not support manually configuring their speed and duplex.

Notably, this is an issue with many Realtek cards, including network interfaces which utilize the re(4) driver.

The settings appear to apply, but the card remains in a duplex mismatch state.

In these cases you can work around the problem with a small managed switch.

Set the speed and duplex of one port to match the upstream, and then set the port facing the affected NIC to autoselect/autonegotiate.