In V100R003 and earlier versions, a combo interface works as an optical interface by default.

In V100R005 and later versions, a combo interface works in auto mode by default and automatically determines the interface type depending on whether the optical interface has an optical module installed:

• If the optical interface has no optical module installed and the electrical interface has no network cable connected, the interface type depends on which interface is connected first. If the electrical interface is connected by a network cable first, the electrical interface is used for data switching. If the optical interface has an optical module installed first, the optical interface is used for data switching.
• If the electrical interface has a network cable connected and is in Up state, the electrical interface is still used for data switching when the optical interface has an optical module installed.
• If the optical interface has an optical module installed and is in Up state, the optical interface is still used for data switching when the electrical interface has a network cable connected.
• If the optical interface has an optical module installed (with optical fibers connected) and the electrical interface has a network cable connected, the optical interface is used for data switching after the switch restarts.

You can use the combo-port command to configure a combo interface to work as an electrical or optical interface.