Fix Double NAT (Two Routers in a Row)

Who this is for: Offices with an internet provider's modem or router plus their own router or mesh Wi-Fi.

What goes wrong

• One-way audio, especially on calls that come in.
• Phones go offline for a while, then come back.
• Calls work for some phones but not others.

Why it happens

NAT (Network Address Translation) is how a router lets many devices share one internet address. Each router that does NAT adds a layer.

With two routers in a row, call traffic has to get through two layers. Each one can time out, block replies, or rewrite traffic differently, so calls break in hard-to-predict ways.

How to fix it

1. Find out if you have double NAT. Look at your setup: if the internet provider's box has its own Wi-Fi or is labeled as a router or gateway, and you plugged another router into it, you likely have two.
2. Pick one router to do the routing. Usually that's your own router, since you control its settings.
3. Put the other box in bridge mode (sometimes called modem mode or passthrough). That turns off its routing so it only passes the internet connection along. Your internet provider can do this for you if you can't find it.
4. If bridge mode isn't available, look for a setting called DMZ, DMZ host, or IP passthrough on the provider's box, and point it at your own router.
5. Restart both boxes, then restart the phones.
6. If you use mesh Wi-Fi, set the mesh system to bridge mode or access point mode so your main router is the only one doing NAT.

Notes for common router types

• On most internet provider gateways, look under Firewall, Advanced, or WAN for Bridge Mode, IP Passthrough or DMZ.
• On most business firewalls, the firewall should be the only device doing NAT. The provider's equipment in front of it should be in bridge mode.
• On most mesh Wi-Fi systems, look in the app under Advanced or Network for Bridge Mode or Router Mode, and switch it to Bridge.

How to tell it worked

• On a computer in the office, check the router's internet (WAN) address in its admin page. If it starts with 192.168, 10, or 172.16 to 172.31, you still have another router in front of it.
• Run the free Net Checker.
• Incoming calls ring and have audio both ways, every time.

More router settings that affect call quality

• Turn Off SIP ALG
• Set UDP Timeouts to at Least 300 Seconds
• Allow Cannon VoIP Through Your Firewall
• Prioritize Voice Traffic with QoS
• Fix Bufferbloat with Smart Queue Management
• Stop Wi-Fi Band Steering and Roaming from Dropping Calls
• Guest and Isolated Wi-Fi Blocking the App
• DNS and Content Filtering Blocking Cannon VoIP
• VPNs and Security Software Interfering with Calls
• Mesh Wi-Fi Systems and Calls Cutting Out
• Wi-Fi Power Saving Causing Missed Calls
• Mobile Hotspots and Carrier-Grade NAT

See all router settings · What makes call quality good or bad