Your router has several Ethernet ports, but they might not all be for the same purpose. The Ethernet ports on the back of your router might seem interchangeable. On some routers they are, but others feature a mix of ports with different jobs and maximum speeds.

One may connect the router to your modem or fiber terminal, while others provide a wired connection for PCs, consoles and other devices around your home. Deciding on the right port depends first on what you're plugging in, then on how fast the devices at both ends can communicate. Start with WAN versus LAN; speed comes after that.

If your router connects to a separate modem or optical network terminal (ONT), the Ethernet cable from that device normally plugs into the router's WAN or Internet port. WAN stands for wide area network; here, it is the router's connection to your internet service. For router/modem combo units, you won't need this connection since one device performs both functions.

The other Ethernet connections are generally LAN (local area network) ports. These are where you connect devices inside your home, such as a desktop PC, game console, smart TV or network-attached storage (NAS). Four LAN ports don't give the router four separate internet connections; they let you connect up to four wired devices directly (rather than using wireless connections).

Some routers feature ports marked WAN/LAN that can perform either job, while other models use auto-sensing Ethernet ports instead of a dedicated WAN jack. The number of LAN ports you need depends on how many devices you want to wire directly to the router. If you run out, an Ethernet switch can add more connections without requiring another router.

Once you're considering the LAN side, the next question is speed. Some routers feature identical LAN ports, while others (like the Netgear Orbi 870) mix gigabit and multi-gigabit connections on the same device. Labels such as 1G, 2.5G, 5G and 10G refer to maximum link speeds of 1Gbps, 2.5Gbps, 5Gbps and 10Gbps.

For example, the TP-Link Archer BE900 shows why checking matters. It has four 2.5Gbps LAN ports as well as 10Gbps connections that can handle either WAN or LAN duties. There is no general rule that port 1 will be faster than port 4 simply because of its position or number.

A 10Gbps port doesn't automatically give every device plugged into it a 10Gbps connection. The rest of the Ethernet hardware has to support the faster speed as well. If your computer has a 1Gbps Ethernet adapter, connecting it to a faster multi-gigabit router port doesn't upgrade what your computer offers.

Copper Ethernet hardware typically uses auto-negotiation to determine a link configuration supported by both ends. The practical result is simple: a 1Gbps ...