Question: Since AirPort Express only has one Ethernet port, does it act as a LAN port, WAN port, or both?
Answer: Depending on how you have it set up, the Ethernet port can function as a LAN port (defined as either simple bridging or sharing your Internet connection via network address translation) or a WAN port (connecting to your broadband Internet service provider or upstream router). However, it never acts as both simultaneously in the way that the original AirPort Base Station (Graphite) can. When the AirPort Express is using network address translation, the Ethernet port acts as a WAN port. When it is set up as a WDS remote station, it can act as a LAN port. Assuming that your Internet service provider only gives you one IP address (the most common scenario for homes), this means that AirPort Express can only accommodate wired clients when acting as a WDS remote base station or bridge. Therefore, if you need to support wired clients and only want to get one base station (or router, as it's the routing capacity of AirPort Express that is relevant here), you should get the AirPort Extreme Base Station instead.
