The Double NAT Problem

13th April 2021

NAT (Network Address Translation) is a well known solution to IPv4 not having enough addresses for the explosion of people and things that want to get connected to the internet. It uses a single IP address on a gateway device, to allow a few thousand devices have access to the internet. For bonus points it also provides a measure of security to those devices, as they are not inbound route-able. Overall a good solution.

Problems happen when your ISP (Internet Service Provider; the company you pay to get you onto the internet) uses a NAT and you have a wiz-bang firewall that also uses NAT.

Double NAT is a confusing problem as Surfing the web still works but many other services do not.
-Using a cloud service to verify your firewall is up
-Tunnel mode IPSec VPN
-Most remote control programs
-Dynamic DNS

Possible Solutions:
-ZeroTier P2P VPN
-user mode IPSec VPN?
-TeamViewer
-IPv6