Router configuration - what does the NAT option mean?

Question

In my router I have this option:

I know what is NAT, but what does it mean the bridge option here? and how the NAT is related to it? what is more secured enable or disabled or bridge?

Answer 1

Missing information: device brand and model. My best guess at the moment:

Enable: device act as a router, external/WAN/ISP interface is connected to one subnet and internal/LAN interface to another. Outbound traffic from LAN to WAN is NATed behind external IP address.

Disable: device act as a router, external/WAN/ISP interface is connected to one subnet and internal/LAN interface to another. Outboud traffic from LAN to WAN is forwarded with original source IP address.

Bridge: device act as bridge/switch, and both external/WAN/ISP interface and internal/LAN interface(s) are on the same network (broadcast domain).

Answer 2

Bridge, I assume, is used for IPX/SPX over TCP/IP and what not. Network Address Translation is for using an internal network with one of the set-aside private blocks like 192.168.x.x, as opposed to classical routing which is a can of worms we will not get into.

Just use NAT.

Answer 3

It depends on your modem/ISP, which you haven't told us.

• Some will require your router to do NAT, and will not work if you disable it.

• In other cases, the modem already does NAT. "Double NAT" is horrible and will almost certainly break UPNP port forwarding, which is required for P2P protocols such as the running a game server, sharing files through MSN messenger, BitTorrent etc.