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Disabling NAT on ADSL modem

Posted on 2009-02-16
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Hi! I have an ADSL modem/router with one WAN port, 1 USB port and 1 Ethernet port (don't use the USB port). no WiFi capabilities.

What I'd like to do is use the modem (BT Voyager 210) purely as a modem only and connect it to a Linksys router.

I'm not really sure how to accomplish this. I can turn off DHCP but when I disable NAT, I can no longer access the Internet on my computer (for now I just have a laptop connected directly to the modem's Ethernet port).

Hopefully someone can help me out with this.

Here is the modem's spec sheet:
http://www.voyager.bt.com/wired_routers/voyager_210/downloads/BT%20Voyager%20210%20Product%20Specifications.pdf

I'd be happy to provide screenshots or a list of features the modem/router supports.
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Question by:Julian Matz
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by:TIsbill
TIsbill earned 80 total points
ID: 23654268
Many DSL Modems have a bridge mode that allow you to do exaclty as you are describing. I'm not familiar with this specific device though.
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MrJemson earned 1040 total points
ID: 23654548
Here is a guide to putting you modem in bridge mode:
http://www.puzbie.co.uk/forum/viewtopic.php?t=143

Once this is done, plug it into your Linksys and configure the WAN on your Linksys as PPPoE with the username and password you had previously used on your modem that were supplied by your provider.
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by:asdlkf
asdlkf earned 880 total points
ID: 23668465
What you need to do is this:

put the modem into bridge mode (i dont have access to the interface obviously so you'll have to figure this part out)

remove any ip addresses or usernames from the bridge (it is now only basicly a 2 port hub. You can put a random BOGON address onto it if you want to manage it by IP afterwords without resetting it, but for the configuration you want, it will effectively have no ip address.)

If you have DHCP addresses from your ISP, plug your linksys's WAN port into the bridge's ethernet port (spec sheet says only 1, but if wrong, use the LAN or PC slot).

Make sure you use appropriate cabling (not sure how the ports are wired, but you probably want a cross-over cable (rather than a straight through). If one doesn't work, try the other type. Link light will tell you if it's right).

If you have a static IP address from your ISP, setup that information in the PPPoE section of the internet section of the linksys configuration page.

The linksys box will need your ADSL username, ADSL password, if you are using DHCP (or not) from your ISP, and optionally ip address, subnet mask, default gateway, and 1 or more DNS servers (and maybe an MTU if your in a non-standard network or if specified by your ISP).

Once all that is setup, configure your linksys's DHCP pool and features as if you had a regular cable connection.

-- Chris
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by:MrJemson
ID: 23674812
No need for a cross-over cable.
It is not the 90's anymore. Things will auto sense now you know :)
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by:Julian Matz
ID: 23675751
Thanks for all the help!

So basically, it sounds like I will need my Linksys router to set this up... I don't have it yet so that's why I tried setting up a direct connection to my laptop just to see if I'd be able to turn off NAT.
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by:MrJemson
MrJemson earned 1040 total points
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Correct.

If you want to test it from your laptop, you can put the modem in bridge modem etc and set up a PPPoE connection on your PC to test.

Assuming you are using Windows XP you can use the following guide to set this up and test it.
http://www.iserv.net/ConfiguringABroadbandConnection/SettingUpAPPPOEDSLConnectionOnWindowsXP.php

The same username and password would be used on the laptop's PPPoE connection as you would put in the Linksys.
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by:asdlkf
ID: 23677062
I put the cabling crossover thing in there because the data sheet on the adsl modem did not include sufficient information on the 10/100 Ethernet port. It said auto sensing, but not auto negotiating.
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by:Julian Matz
ID: 23677867
Cool, thanks!

This might be slightly off-topic, but I just want to be sure I get the right equipment...

Basically, what I have is a 3-storey building. Currently, my 802.11g signal barely makes it to the 2nd floor (I have a wireless router/modem on the ground floor).

I'd like to improve this and thought of connecting a Linksys WRT54GL to my modem and attach 2 high gain antennas to the WRT54GL.

However, I also need at least one RJ45 port for an ethernet connection on the second floor, so I then thought of keeping my existing wireless router on the ground floor and using the WRT54GL on the 2nd floor in some type of bridge mode.

I don't think I'm fully clear on the terminology/functionality though. What exactly do I need? A bridge, AP, wireless extender/repeater, WDS, or a combination of these?
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by:Julian Matz
ID: 23677983
Actually the above probably warrants a new question so I've posted it here:
http:/Q_24156850.html

Thanks again for the help. I will close this one shortly.
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by:asdlkf
ID: 23678719
I'll put this in the other question aswell...

You want:

adsl modem (bridge mode) <------->(any wirless router - linksys will do) <--- ( ( ( wireless ) ) )--->(wireless bridge with built in ethernet switch) <-----> PC's.


You might also want to look into powerline networking. Basicly instead of transmitting the data wirelessly (which can be subject to interferance from microwaves/etc/etc/ walls/ whatever, it transmits over the cables in your electrical wiring. (it uses the power wiring in the power outlet system of your building to conduct the communications signaling). it would look like this:

adsl modem (bridged) <--->wired linksys router<--->Powerline bridge<---power cables--->Powerline bridge<--->switch<--->PC's.
Concept picture:
http://www.homeplug.org/products/plc_networking1.jpg



For example, a pair of these:
http://www.netgear.com/Products/PowerlineNetworking/PowerlineEthernetAdapters/XE102.aspx
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by:Press2Esc
ID: 23681389
Although I like Powerline technology, they have a 50% chance of working.  There is still no adopted universal (IEEE) standard and the adapters do not work across power phases...
 
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by:Frosty555
ID: 23686419
Please see my comments on powerline networks in your other question. I agree with Press2Esc, they're unreliable.
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by:Julian Matz
ID: 23842039
Thanks for all the info! Closing the question now... Just have one more question relating to NAT - basically, I thought this was needed for multiple devices connected to one gateway to function correctly, hence I didn't understand why NAT would be required for a single port router, but am now wondering if NAT might be required for connections that have only a single public IP at any given time??
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by:Julian Matz
ID: 23842071
Also, are there any disadvantages of having a double (or multiple) NAT system - e.g. two or more devices on same network with NAT enabled? I would presume it would have some disadvantages since NAT, from what I understand, seems to be a bit controversial in the first place.
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by:MrJemson
ID: 23842148
NAT is a method of allowing many computers (with private IPs) to access the internet by masquerading as the one public IP address.

Essentially your computer sends the request (Perhaps for a website) to the router, the router forwards it on to the external source, but maps the connection details in its NAT table (Eg
Source IP, Destination IP, Source Port, Destination Port) so that when the server responds it knows where to send the returned request. By doing this multiple devices can access different services on the internet all from the one public IP address.

For your second question:
NAT is good. It provides firewall capabilities (Nothing can get through the NAT unless specifically allowed) and allows multiple computers to get out to the internet without having to have a public IP address for each PC.
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