Cable Modem Configuration - VPN

HandyMac · 29-12-2006, 13:41

Please note that I am broadly familiar with PC networking and TCP/IP, so I don't need the idiots guide to do network configuration, I just need to know the basics for making the following change happen.

I have NTL broadband which is working perfectly. Unfortunately (or not) I have a need to use a VPN tunnel to connect to a remote location. Problem is that VPN won't work because both sides of the VPN tunnel are using the same IP subnet (192.168.0.x/255.255.255.0). So one of them has to change.

Configuring my end of the network I have no problem with, until I get to the NTL cable modem bit. I don't even know what it's IP address is but I guess it'll be on the 192.168.0.x subnet (feel free to correct me if I'm wrong!). I'm assuming that I will have to change the CM's local IP address.

So, how do I go about connecting to this cable modem to carry out a change of its IP address? I seem to recall from when the CM was installed it was configurable via a browser, but for the life of me I can't remember the details. If I could get to the CM's control panel I'm sure I can figure the rest out.

I'm on a 10M connection and the CM is a small blue box about 4x5x1in. No make or anything I can find. It has both an RJ45 and a USB socket on its rear end (only the RJ45 is connected). I'm sure this is a regular NTL CM.

So basic information about how to get to the CM control panel (with passwords if necessary) would be gratefully received.

Cheers,
Andrew

Paul K · 29-12-2006, 14:16

Changing anything within the modems config screen is a no no. The modems public (external) IP adress will more than likely begin with 10.xxx etc and if you ping an address via a CMD prompt you should get it. Or just try ipconfig /all

HandyMac · 29-12-2006, 14:30

Thanks Paul. I did an IPCONFIG /ALL from a command prompt, no 10.x addresses anywhere, and no addresses I don't immediately recognise.

The 192.168.0.1 gateway address I can see is my NetGear FVS318 firewall/router, and that's sitting between the cable modem and my network.

I know this may sound a bit thick, but do I assume that I won't need to change anything on the cable modem? I can obviously change the FVS318 to a new IP address no problem, but I'm not sure whether it will rely upon another address on the other side of itself (which I can't see with IPCONFIG).

Just worried that if I move the 192.168.0.x addresses to 192.168.1.x I will lose my NTL connection.

Andrew

Paul K · 29-12-2006, 14:33

Have you tried a tracert? That will show the IP address as the route begins. You will need your external IP address as that is the one that your tunnel will aim at.

29-12-2006, 14:34

Quote:

Originally Posted by HandyMac

Thanks Paul. I did an IPCONFIG /ALL from a command prompt, no 10.x addresses anywhere, and no addresses I don't immediately recognise.

The 192.168.0.1 gateway address I can see is my NetGear FVS318 firewall/router, and that's sitting between the cable modem and my network.

I know this may sound a bit thick, but do I assume that I won't need to change anything on the cable modem? I can obviously change the FVS318 to a new IP address no problem, but I'm not sure whether it will rely upon another address on the other side of itself (which I can't see with IPCONFIG).

Just worried that if I move the 192.168.0.x addresses to 192.168.1.x I will lose my NTL connection.

Andrew

The external ip will be issued by dhcp. Look in your router for the wan address.

this tool should help you

http://www.broadband-help.com/tools/clientInfo.aspx

You cannot change the external ip of your modem as it is issued via dhcp and is not fixed on a residential service.

Stu038 · 29-12-2006, 14:34

After much messing about a couple of years back the only way I could get VPN to play was by changing the subnet of my internal network to something other than 192.168.x.x I use a 12.x.x.x subnet now and let the router handle all of the NAT stuff, it seems to work fine, she who must be obeyed regularly connects into the systems of the companies she does work for with no problems.

The ntlTW DHCPs assign a "broadcast" IP address to the modem and a "private" address to your PC/router, unfortunately there's no way that you can adjust those, but if you want to have a nose about a search of the forums will provide you with the address you need to logon to the modem, passwords etc. Theres also been several similar threads over the years so one of them may be able to provide you with more info.

HandyMac · 29-12-2006, 17:37

Useful information - thanks everyone.

I guess that maybe my NetGear FVS318 might not care about the IP address it is getting its broadband feed from, and maps that up automatically based upon the fact that the incoming broadband is on a separate port. In which case I only have to worry about the local 8 ports on its bum being on the same subnet.

Andrew