Improperly configuring a secondary router as a standalone device instead of an access point can create a double NAT issue that disrupts smart home connectivity and remote access services.

Key Points

• Double NAT occurs when two routers on a single network both perform network address translation, creating two stacked private subnets.
• Common symptoms include failed port forwarding, unreliable smart home device discovery, and connection timeouts for self-hosted services like Jellyfin or Vaultwarden.
• Users can diagnose the issue by checking if a secondary router’s WAN IP address is a private IP range rather than a public one.
• Running a traceroute can confirm the problem by showing multiple hops through private IP addresses before reaching the public internet.
• Switching a secondary router to "Access Point Mode" disables its DHCP and NAT functions, allowing the primary router to manage all network traffic.

Why it Matters

Double NAT often goes unnoticed because it does not impact basic web browsing or video streaming, leading users to incorrectly blame their ISP or hardware for intermittent connectivity issues. Properly configuring network topology is essential for maintaining stable peer-to-peer connections and ensuring that self-hosted applications remain accessible from outside the home network.