DIAGNOSIS The WAN (Internet) port isn't getting a valid IP address from your modem. This is almost always a handshake or cable issue.
FIX Power cycle the entire chain in the correct order.
- Turn off the router and modem.
- Unplug the Ethernet cable from the router's WAN port (the blue one) and plug it back in firmly.
- Turn on the modem, wait 2 full minutes for all its lights to settle.
- Now turn on the router. The red light should turn white/blue within 90 seconds.
IF THAT DIDN'T WORK Log into the router (router.asus.com) and check the WAN connection type. Go to WAN > Internet Connection. If your ISP uses DHCP (most do), ensure it's set to Automatic IP. If you have PPPoE, enter your credentials here.
HEADS UP Never connect the modem's Ethernet cable to one of the yellow LAN ports by mistake. It must go to the single, separated blue WAN port. A red light means it's in the wrong port.