NAT Configuration (cheekily fixed tripple connection to NTL)

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Chris Corbyn
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NAT Configuration (cheekily fixed tripple connection to NTL)

Post by Chris Corbyn »

Hi,

I'm trying to network a few PC's on a cable connection. Unfortunately the cable modem will only issue 1 IP so multiple users cannot use it by a simple hub/switch addition and the modem must be rebooted to issue a new IP to another PC wishing to use the net if somebody else was using it earlier.

I have an old ADSL router which has NAT on it. I've read that my particular cable modem will allow multiple PCs to onnect if you add a router with NAT so all PC' s appear as the issued IP of the modem.

I can't quite understand how to do it or if it's even possible with the ADSL router (I know you can use as a normal router for DHCP etc without connecting to ADSL).

The cable modem during this session has given me the following:

IP: 81.108.149.201
Subnet: 255.255.255.0
Gateway: 81.108.149.254

The ADSL router will issue IP's 10.0.0.4 --> 10.0.0.15 (unless defined by user in the settings). It's own IP is 10.0.0.2 and the default gateway it issues is 10.0.0.2

In the NAT setting you chose the adapter (Pvc1 - correct me if I'm wrong, for the LAN) and a User IP (You can list a few).

How do I go about sharing this connection so it looks as if all PC's are 81.108.149.201?

My method so far was to connect a PC to the net and run ipconfig to get the details. Then enable DHCP on the ADSL router and put the address 81.108.149.201 in the NAT but it doesn't work.

My networking knowledge is poor so forgive me if I didnt make much sense :-)

BTW: I connected one PC - got the IP, default gateway and subnet then pulled the pc of the network while the modem was still connected. Went to another PC, put those settings in the TCP/IP properties but it wouldnt go on the net even though the gateway could be pinged. (MAC address issue?)

Thanks :-)
Last edited by Chris Corbyn on Thu Dec 23, 2004 7:41 pm, edited 1 time in total.
timvw
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Post by timvw »

actually, all you need to do is:

[pc1] --- [router local/lan]
[pc2] --- [router local/lan] = [router extern/inet] --- [cable modem]
[pc3] --- [router local/lan]


this way:

your cable modem will only know the mac address of your router. (it will give your router a public ip)

your router can provide the lan interfaces an ip through dhcp (it will give your pc's an internal ip)
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Chris Corbyn
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Post by Chris Corbyn »

I was playing around a bit last night and what I did was to connect the modem to the router and leave it to establish a connection (and supposedly issue an IP). Then I connect my PC to the router but all that happened was that my PC picked up the IP issued by the cable modem, not the router (normally 10.0.0.7 from the router:- I got 81.108.148.2 from the modem?).

It's as if the modem cannot talk to the router (maybe to do with the fact it's IP is set to 10.0.0.2 and the cable modem wants to issue it a dynamic IP).

I have changed the subnet mask of the router to match the cable modem but it doesn't help.

Do I need to make the ADSL modem somehow think that the cable modem is the WAN itself? How I do that I don't know. I can change the WAN settings for Pvc0 thru to Pvc6 (Static IP, Subnet, Default gateway, DHCP client name etc).

This probably seems really simple to most people but I'm not too good with the hardware config stuff.

Thanks for helping me out
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Chris Corbyn
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Post by Chris Corbyn »

Unfortunately the ADSL router only has one ethernet port so you have to connect it to a swicth to allow it issue IP's to multiple users.

I've set it up like this Image

Should this make a difference?

If the image does show click here http://musick.4t.com/diag.JPG
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Chris Corbyn
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Post by Chris Corbyn »

Just read this...

http://adsltech.com/portal/forum/forum_ ... able+modem

Looks like it's not possible. That router they mention in the post is mine except with 4 ports not just one.

I wonder if you can somehow convert the RJ11 connection to RJ45 (probably cheaper to get a generic broadband router instead of ADSL specific)
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Weirdan
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Post by Weirdan »

why would you use external (and rather limited in capabilities) router when you already have full-functional pc? just get one additional network card (i believe they pretty cheap nowadays, about a 6 USD or so) and put it into one of your boxes. Then set up a NAT (or a proxy) on that box - and voila, you're ready to surf.
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Chris Corbyn
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Post by Chris Corbyn »

Come on I'm well pleased!!! Just got it working and it looks to be better than expected.

I downloaded an app called aMac from download.com.

It lets you change your mac address. I set all the pc's on my network to the same mac address, hooked them together with a switch, plugged in the cable modem and voila - all pc's were given a unique WAN side IP and default gateway and can access the net.

Also, from my observations thus far, we each have the full 300K connection (not shared) - shhhh... don't tell anyone :-)
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Chris Corbyn
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Post by Chris Corbyn »

Weirdan, your idea was good but the pc's are all in bedrooms and non of would want a pc turned on 24/7 when we're trying to sleep. Seems my fluke of a fix works pretty well. I made a note of the original mac addresses so they can be changed by if the need arises.
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Post by timvw »

don't need to donwload stuff to change your mac address ;)

linux etc have ifconfig with the -HW option if i'm not mistaken
windows (2k,xp) networking -> advanced config tab or something like that
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Chris Corbyn
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Post by Chris Corbyn »

Oh, now there's something I didn't know. Thanks for that.
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