Bridge mode lets you connect two routers without the risk of performance issues. Bridge mode is the configuration that disables the NAT feature on the modem and allows a router to function as a DHCP server without an IP Address conflict.
Connecting multiple routers can extend the Wi-Fi coverage in your office/home. But when you have two routers -- each with their own private Wi-Fi network -- your personal devices can have a hard time communicating with each other. This scenario is called Double NAT.
For example, let’s say you want to wirelessly print a picture from your computer. If you have two Wi-Fi networks, it’s possible that your computer is on one network while your printer is on the other. And if both networks are private, your computer won’t be able to tell your printer to print the picture.
Bridge mode fixes this by letting multiple routers share one single Wi-Fi network. When do I need Bridge mode?
When two NAT devices are connected in series (for instance a modem with built-in NAT capabilities is connected to a router which is also a NAT device), it is advisable to configure your modem in bridge mode to avoid conflicts.
What is NAT? In computer networking, the process of Network Address Translation (NAT) involves re-writing the source and/or destination address of IP packets as they pass through a router. NAT allows multiple hosts on a private network to access the internet using a single public IP address.
The modem has to be bridged before connecting to a router since applications like VPN, P2P, and remote management require a public IP Address on the router WAN port for a successful connection.