When to put modem into 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.

What is bridge mode?

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.

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.

Note: You will need to call your Internet Service Provider for the bridge mode settings.

Here is a list of common service providers and modems that may require setting modem to bridge mode:

Note: This list identifies only the common models and does not cover all modems.

Modems:

• Westell 2100

• Westell 2200

• Westell 6100

• Speedstream 5100B

• 2 Wire

• Zyxel

• Netopia

• Sprint 645 series

• Paradyne

• Veragia

• Broadexant

• Draytek 2400

• Comtrend Cd 507

• Arescom 800

• Zyxel Prestige 623-40

• MSN DSL 1000

• Tranzeo

• Vision net

Internet Service Providers:

• AT&T

• Sprint

• Verizon

• Bellsouth

• CenturyTel (Century Link)

How to identify NAT modems:

1. Connect the computer directly to the modem Ethernet (LAN) port.

2. Click Start > Run > Type cmd (command for Windows) and press Enter.

3. On the command prompt, type ipconfig and hit Enter.
   To view your IP address on Mac computers or Windows 8, see What is the IP address of my NETGEAR router?

4. If the IP Address displayed under Ethernet Adapter Local Area Connection is either 192.168.x.x or 10.0.x.x, then the modem should be bridged.
   Call your Internet Service Provider to set the modem to bridge mode.

5. You can also try changing LAN IP address of router.
   Log in to the router user interface and change IP address to 192.168.2.1 or 10.0.0.1 under LAN Setup (ADVANCED > Setup > LAN Setup).
   If you need assistance with router login, see How do I log in to my NETGEAR home router?

Source:

https://kb.netgear.com/000028987/When-to-put-modem-into-bridge-mode

https://gospeedcheck.com/article/how-to-access-arris-modem-in-bridge-mode-1118