Double NAT Detected

Understanding what Double NAT means and how to resove it

Table of Contents

What does Double NAT Detected mean?

What does Double NAT Detected mean?

"Double NAT" occurs when you have two routers connected back-to-back (for example, a Wi-Fi mesh node plugged into an ISP router that is not in modem-only mode). This creates two layers of address translation, which heavily disrupts the real-time audio (RTP) required for VoIP calls, leading to one-way audio or dropped calls.

How to fix it:

  1. Enable Bridge/Modem Mode: If you have a third-party router (like Eero, Google Wi-Fi, or Netgear), ensure your ISP-provided router is set to "Modem Only" or "Bridge" mode.
     
  2. Remove Redundant Equipment: Do not daisy-chain routers. If you need more ports, use a standard unmanaged Network Switch rather than a second router.
     
  3. Check CGNAT: Some rural broadband, 4G/5G, or Starlink connections use Carrier-Grade NAT (CGNAT). You may need to ask your ISP for a static, public IPv4 address to resolve this.