What is a "Double NAT"?
NAT (Network Address Translation) allows your devices to share a single WAN IP address (provided by your Internet Service Provider) by changing the public IP address to a private IP address. This process also secures your network by blocking any direct access to your local IP address.
Double NAT is when you connect your router behind another router creating two different private networks. For example, connecting your NETGEAR router behind a modem/router provided by your ISP. Double NAT does not prevent your devices access to the internet but may cause problems with playing online games, opening a specific service port, connecting to a VPN tunnel, or visiting secure sites with SSL. Also, the devices connected to the first private network may not be able to communicate to the devices connected to the other private network.