Engadget: Adding a second router usually isn't the answer for weak Wi-Fi

A home router creates a local network and uses Network Address Translation, or NAT, to let connected devices share an internet connection while sorting traffic. Most homes only need one device doing the actual routing, Engadget says. When a second router is connected in normal router mode behind the first, it creates another private network and performs NAT again, a condition known as double NAT. That typically does not make ordinary web browsing or streaming noticeably slower, but it can cause problems for online gaming, port forwarding, and Universal Plug and Play. Two separate home networks can also make it harder for devices to find each other, so a computer on one router may not reach a printer on another even in the same house.

For weak Wi-Fi coverage, mesh systems are built to extend one network throughout a home with nodes that work together instead of creating independent routed networks. Many existing routers can also be reused in access-point mode, in which the device only acts as a Wi-Fi connection point while the primary router continues managing routing and firewall functions. If the room with weak Wi-Fi has an Ethernet connection, a router set to access-point mode can use that wired link to extend coverage, Engadget says. When coverage is already fine and more wired connections are needed, an Ethernet switch adds ports without introducing another routing layer.

Internet providers often supply a gateway that combines a modem or fiber connection with router functions and Wi-Fi. Plugging a separate router into that gateway and leaving both devices in their default modes can produce double NAT. Engadget says users who want their own router to manage the network should check whether the ISP gateway supports bridge mode, which stops the gateway from acting as a router. Alternatively, the secondary device can run in access-point mode, letting the ISP gateway handle routing while the extra device mainly improves Wi-Fi coverage. The trade-off is that some router features may stop working; Engadget notes TP-Link says access-point mode disables NAT forwarding, VPN, QoS, and some parental controls.

Running two active routers is only justified in setups where separate networks are intentionally desired, such as a home lab that keeps experimental devices and services away from the main network, according to Engadget.