[Wiltshire] Meeting 8 th December 2008

[Simon Fryer]

G'Day,

This is quite an interesting problem....

On 11/12/2008, dianne reuby <pramclub at yahoo.co.uk> wrote:

> > How are you connected? Do you have ADSL down a phone line or a Virgin
> cable
> > modem? Do you use a separate router? Does it have WiFi? Do you use it?
>
> > Tell us exactly what you have and use, then somebody might be able to help
> get
> > you running.
> It's really odd - I've used virgin/ntl for years, and had no problems with
> Ubuntu since I first tried it two years ago - worked immediately. But I was
> using a USB connection rather than ethernet, mainly because we never got
> round to buying a cable. :)  We just plugged the modem into whichever PC we
> were going on line with - they're next to each other so it was no hassle and
> we rarely wanted to be online at the same time.
> When we had the problem recently, the engineer put a new modem on for us as
> ours was quite old, but it only has ethernet. Ubuntu finds my card, but
> won't connect. Hence trying different cards, cables, slots, routers. XP is
> fine - although it shouldn't be, because the IP address it's using isn't the
> router default. We can't log into the router to change it, but it still
> works, which is another mystery.I have exactly the same problem with or
> without a router - going straight to the modem makes no difference.
> That's why I'm getting desperate enough to reinstall XP, so I can at least
> phone tech support and let them use their crib sheet to see if we can fix
> it, then revert to Ubuntu.  Good job my husband never gets rid of his old
> hard drives!
> Dianne

Based on my experianced with NTL for a couple of years up till the end
of 2005, I developed some understanding of how it works. I am assuming
that NTL have not really changed the way their network works since.

You are authenticated on the NTL network through the MAC address of
the modem. Assuming you can connect at least one computer through the
modem, the modem (and NTL) is fine. Although you should probably check
the DHCP leases to make sure that you are getting a lease longer than
5 to 10 minutes. NTL will give anything a short lease - long enough to
setup the modem as being valid.

The idea is that the computer connected to the modem then DHCPs an
address, DNS servers and default gateways etc for the NTL network
through the modem. The modem, not being particularly bright, then sets
its ARP table for the MAC address of the computer.

I am still a bit fuzzy as do the actual setup you are using.

If you are just moving the ethernet patch leads between the computers
then you will need to reboot the modem to clear the ARP table within
the modem.

If you are running both computers through a router (not hub or switch)
then can the XP box and the Ubuntu box see each other? I suspect the
XP box is DHCPing a lease before the Ubuntu box and getting the IP
number for the network access.

I think the solution for what you want to do is set the router to DHCP
NTL network details from the modem. The router then needs to act as a
DHCP server for the XP and Ubuntu box and perform NAT between the XP,
Ubuntu machines and the NTL network.

Good luck.

Simon

-- 
------------------------------------------------------------------------
"Well, an engineer is not concerned with the truth; that is left to
philosophers and theologians: the prime concern of an engineer is
the utility of the final product."
Lectures on the Electrical Properties of Materials, L.Solymar, D.Walsh