RJ45 Explained: The Ethernet Connector on Routers

What Is an RJ45 Port?

An RJ45 port is the rectangular socket on a router that accepts an Ethernet cable. It is the wired network port you use when you do not want to depend on Wi-Fi for a particular device. The connector has a small latch that clicks into place, and the same style of port appears on modems, network switches, computers, media players and mesh nodes.

RJ45 is also the term people use for the Ethernet connector found on LAN and WAN ports. For buyers, the practical definition is simple: the RJ45 port is where an Ethernet cable goes. If you are comparing routers, the port layout matters as much as the Wi-Fi standard, because the wired ports carry traffic to your modem and to the devices you choose to connect by cable.

What RJ45 Ports Do on a Router

Routers typically separate their RJ45 ports into WAN and LAN. The WAN port connects the router to the modem, ONT, or upstream network. LAN ports connect local devices, switches and mesh satellites. When shopping, the number of LAN ports tells you how many devices you can wire directly without adding a switch. See router ports, WAN port types and how many Ethernet ports.

A wired connection through an RJ45 port is often a good choice for a desktop, game console, smart TV or mesh satellite. It keeps that device off the Wi-Fi airtime and gives it a direct path to the router. The tradeoffs between wired and wireless are covered in Ethernet vs Wi-Fi.

• WAN port: connects the router to the modem, ONT or upstream network
• LAN port: connects a PC, game console, smart TV, switch or mesh node
• Wired backhaul: uses an Ethernet jack on a mesh node to carry traffic between nodes

Same Connector, Different Capabilities

The RJ45 shape tells you only how the cable fits, not how fast the port is. Router makers use the same physical connector for standard Ethernet ports and for faster multi-gig ports. When comparing models, check the port speed class and the number of faster LAN ports instead of assuming that identical connectors are identical ports.

Some routers include SFP ports as an alternative to RJ45. SFP is a different port shape that accepts a removable module, commonly used for fiber connections. If your internet service arrives over fiber, SFP vs RJ45 WAN ports explains the difference.

Ethernet cable quality also matters, but the connector fits the same way. A router's RJ45 port accepts a standard Ethernet cable with an RJ45 plug, and the port specs tell you which speed class the router supports.

RJ45 and Your Network Layout

RJ45 ports are part of the wired side of your network, while Wi-Fi is defined by the IEEE 802.11 standard for wireless LANs. The IEEE 802.11-2020 standard describes the medium access control and physical layer specifications for wireless LANs. When you connect through an RJ45 Ethernet port, you are using wired networking; when devices connect over Wi-Fi, they use an 802.11-based link. See Ethernet for the wired side.

You do not need to plug every device into a router's RJ45 ports. A network switch adds extra Ethernet ports, and a mesh system can use Ethernet backhaul to connect nodes by wire. In a typical home network, the router is the center, and RJ45 cables run to the modem and to the most important stationary devices.

Wired backhaul is one reason to pay attention to RJ45 ports on a mesh system. If a node has an Ethernet jack, you can run cable between it and the main router, which may be more consistent than relying only on the wireless link. The tradeoff is that you need cable runs, while wireless backhaul keeps installation simpler.

How Many RJ45 Ports Do You Need?

A small home network may leave most LAN ports unused, but a desktop, smart TV or game console changes the picture. If you prefer to wire several devices, look for a router with enough LAN ports for them, or plan to add a network switch. The decision is explained in the router port guides above.

Mesh routers change the calculation. A satellite with an Ethernet jack can serve a wired device, and a wired connection between the main router and a satellite creates an Ethernet backhaul. The difference between wired and wireless backhaul is covered in Ethernet backhaul vs wireless backhaul.

Security and Wired Ports

RJ45 ports are not just a convenience. A device plugged into an Ethernet port bypasses Wi-Fi encryption, so physical access to the port can matter. Keep the router where only people you trust can reach the ports, and consider disabling unused ports if your router supports it. Public resources such as NIST's Small Business Cybersecurity Corner highlight practical steps to manage cybersecurity risk, including protecting the devices attached to your network.

For the wireless side, the Wi-Fi Alliance says WPA3 is mandatory for Wi-Fi CERTIFIED devices and requires Protected Management Frames. That protects Wi-Fi connections; the wired side relies on the physical port, your router firewall and the rest of your network setup. See router security basics for a broader view.

What to Pick

If you are buying a router, do not choose only by Wi-Fi specs. Check the RJ45 port layout: a WAN port for the modem or ONT, enough LAN ports for your wired devices, and the right port speed for your internet plan and local transfers. The best multi-gig port routers guide is the starting point when you need faster wired ports.

For most buyers, a current router with standard Ethernet LAN ports is enough. Wi-Fi 6 and Wi-Fi 7 give you strong wireless performance, and the Wi-Fi Alliance lists features such as 320 MHz channels, multi-link operation and 4K QAM for Wi-Fi 7. Those features improve wireless links, while RJ45 ports handle the wired connections. Compare Wi-Fi 7 routers for the wireless side, and use the buying guides for your port needs.

What to pick for your use

Questions

Is an RJ45 port the same as an Ethernet port?

For router buyers, yes: an Ethernet port on a consumer router uses the RJ45 connector shape, and you use the same twisted-pair Ethernet cable. Ethernet is the broader technology, while RJ45 describes the physical connector.

Can I use an RJ45 port for a mesh node?

Yes, if the mesh node has an Ethernet jack. Plug the main node into the router's LAN port, then connect another node through one of its Ethernet ports to create a wired backhaul. This is commonly called Ethernet backhaul.

Do RJ45 ports affect Wi-Fi speed?

They do not directly change your Wi-Fi signal, but moving heavy traffic to Ethernet leaves more wireless capacity for other devices. A wired backhaul between mesh nodes can also improve the Wi-Fi that nodes broadcast.

Do I need a special cable for an RJ45 port?

Use an Ethernet cable with an RJ45 plug. The port defines the connector shape; the cable category and termination affect signal quality. Avoid forcing an Ethernet plug into a smaller telephone-style jack.

Are all RJ45 ports the same speed?

No. The connector shape is the same, but the electronics behind the port differ. Check the port speed class on the spec sheet, and consider a router with faster wired ports if you need them for a fast internet plan or local file transfers.