Short answer: your new router may be using WPA3 security or Wi-Fi 7 features that an older device can’t handle. Check the router’s security setting first and use WPA2/WPA3 transition mode. If a device still won’t join, try WPA3-Personal compatibility mode if your router offers it, or give older devices a separate WPA2 network. Then look for device updates. Turning off Wi-Fi 7 features is a last resort, because it takes them away from every device on that network.

If several devices fail, including new ones, the cause is probably something else; start with can’t connect to Wi-Fi.

Why an upgrade can lock older devices out

Security is the usual reason. The Wi-Fi Alliance has required WPA3 support in new certified devices since 2020, and WPA3 is mandatory in the 6 GHz band. ASUS says some older smart-home devices may be incompatible with WPA3, and that many Wi-Fi 7 routers default to it. Apple says WPA3 works with all Wi-Fi 6 devices and some older ones.

First: confirm it’s a WPA3 problem

Look at the security setting on your router’s main network. If it’s WPA3 only, and new phones connect while one or more older devices fail with the right password, WPA3 support is a likely cause. Some routers already default to a mixed mode: ASUS’s main network, for example, defaults to WPA2/WPA3-Personal. If yours is already mixed, skip to step 2.

To check a device, ASUS suggests asking its manufacturer or looking it up in the Wi-Fi Alliance’s Product Finder. Router settings are covered in how to log in to your router.

Step 1: use WPA2/WPA3 transition mode

Transition mode lets WPA3 devices connect with WPA3 while older devices use WPA2, with one password for both. The Wi-Fi Alliance notes that if the password stays the same, existing devices can connect without being set up again. Apple recommends this mode for compatibility with older devices. What you give up compared with WPA3-only is covered in WPA2 vs WPA3.

Step 2: if transition mode isn’t enough

Transition mode doesn’t fix every device. The Wi-Fi Alliance acknowledges that some legacy or uncertified devices have interoperability problems with transition-mode networks. It offers two ways round that. Both leave the older devices on WPA2, so they don’t get WPA3’s protections; WPA2 vs WPA3 explains the difference.

WPA3-Personal compatibility mode. This mode hides WPA3 from older devices, so they connect with WPA2 while updated devices use WPA3 on the same network. It requires updates to the router (access point), and the Wi-Fi Alliance asks makers to label it “WPA3-Personal compatibility”. If your router’s security list shows it, try it before setting up a second network, since it keeps one network for everything; keep the firmware current either way (see how to update your router firmware).

A separate WPA2 network. The Wi-Fi Alliance’s other alternative is two networks on the router, one WPA3 and one WPA2, with different passwords. Your phones and laptops stay on WPA3, and the stubborn devices get a WPA2 network of their own. Some ASUS Wi-Fi 7 routers, including the RT-BE58U and RT-BE55, build this in as an IoT network whose default security is WPA2-Personal. ASUS says it needs firmware 3.0.0.6.102_34946 or later; the menu is called Smart home Master on older firmware and was renamed Network from version 3.0.0.6.102_35404.

Step 3: update the device

If you haven’t already, check the device maker’s site for a firmware update. The Wi-Fi Alliance notes that some existing devices gain WPA3 support through a software update.

Step 4: Wi-Fi 7 settings, as a last resort

Some devices struggle with Wi-Fi 7 itself rather than security. For devices that can’t work with Wi-Fi 7, ASUS describes turning off Wi-Fi 7 mode on the main network, or turning off MLO, Wi-Fi 7’s multi-link feature. On the ASUS Wi-Fi 7 routers that FAQ covers, both are on by default.