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Router/DSL modem in bridge mode

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aneesholv

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What is the intention or purpose of configure a router/DSL modem in 'bridge mode'. Can you tell a scenario which router/DSL modem
work in bridge mode ?
 

Typically you config your DSL/cable modem in bridge mode so as to by-pass the modem and drop the IP on the router; this lets you manage the router almost like a typical WAN connection without the price.
 

By putting the DSL modem in bridge mode, you remove a layer of NAT'ing (Network Address Translation) in your network. Bridging the router makes it act like a "transparent" converter box, so it doesn't have to process the packets coming to it from either direction... it simply forwards them to the next device in the path (either from the ISP directly to your router, or from your router directly to the ISP).

For the most part, it doesn't buy you much performance, unless you run your modem at near-saturation the vast majority of the time... which is highly uncommon for home users. Most ISP's don't run modems near their max bandwidth (you have a profile that is loaded into the modem by the ISP, which defines which speed package you are on... so the modem throttles your speed). So it's even less likely that you could even reach the rate of data processing where double-NAt'ing would be the first thing to impact your xfer rate.

Double-NAT'ing will impact your ping times, but only by a few ms... and it you are talking to servers on the net, those numbers are in the 10's of ms, so 1-2 more is small potatoes.
 

Double NAT’ing doesn’t even make sense???

Using bridge-mode or not you’re only going to get 1 IP from your ISP, either way you’re going to need some other device to provide DHCP/DWG for other LAN users; the cable modem translates the data from either the DSL/Telco or cable/cable provider to 802.3/usb; sorry if I’m just stupid but where is this double NAT’ing that you mention.
 

Using bridge-mode or not you’re only going to get 1 IP from your ISP

This is true at the modem's external interface (to the ISP), but a number of ISP's offer a combo modem/router unit to customers. This is how they support Wifi with just a modem (Qwest, now CenturyLink, did this for many years). The DSL modem/router would have one IP presented to the telco, but would give a 192.168.x.x pool for internal IP addresses... thus, it's providing NAT. If you hung your own (say Wireless-N) router behind the DSL modem and left it w/ default settings, it would generate another NAT.

Most cable companies that I've come across don't have that option, but a number of DSL companies I've worked with, do. If the modem is providing DHCP and a pool or private IP addresses, double-NAT'ing would occur. It's in that situation that using bridge mode is beneficial ("your" router does the DHCP and NAT, and it's external interface handles any authentication w/ the ISP... then the modem/router unit is simply transparent).

**broken link removed**
 

I get it; sorry but I work in enterprise only so I never would have thought about what your saying.
The other thing with bridge mode is that typically the customer is paying for a static IP so as to be configurable for admin, remote access, traps ect.
 

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