PC won't connect to Inet at different location


B

bill a

I had an old desktop pc with Win2000Pro connected on my DSL router and fully
updated Windows, etc and the internet connection worked fine.
I gave the box to a friend who uses a cable modem, and the box will not
connect to the internet there (no router).
The desktop settings have been the vanilla settings: obtain IP and DNS
addresses automatically, DHCP enabled, etc. The tray icon shows when the
cable is plugged in. The same modem and cable work fine when a laptop is
connected to it.
I had the guy put the laptop back on and run ipconfig so I could get the
gateway IP.
With the desktop, I could not ping the IP for the gateway address that
showed in the laptop's ipconfig.
Is there a procedure I should run to reset something after moving from a LAN
with a router to a direct connection to a cable modem?
 
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G

Greg Russell

In
bill a said:
I had the guy put the laptop back on and run ipconfig so I could get
the gateway IP.
With the desktop, I could not ping the IP for the gateway address
that showed in the laptop's ipconfig.

But did the ipconfig on the desktop show that was was configured properly,
with an IP address, netmask, DNS servers and gateway to match that of the
laptop? (different IP address though).
Is there a procedure I should run to reset something after moving
from a LAN with a router to a direct connection to a cable modem?

Two things:

1) Are you using a crossover cable for the direct connection to the modem?
Some ethernet interfaces will automatically deal with either a crossover or
patch cable, but others are insistent on a crossover cable for such a direct
connection. It may be that the two machines' interfaces differ in their
capacity for such a cable as you're using.

2) Assuming out-of-hand that the "ipconfig /all" settings are identical for
both the desktop and the laptop, and that only one of them is "directly"
connected at any given time, it sounds as if the cable modem is expecting
the direct conecction to the MAC address of the laptop which differs from
the MAC address of the desktop ... this is called the "Physical Address" in
your ipconfig output and it consists of 6 hexadecimal numbers such as:

Physical Address. . . . . . . . . : 00-20-18-C0-BB-84

The same problem happens when a simple "switch" is used to allow both of
your computers to be connected. The switch knows which MAC is connected to
each port on the switch, and swapping those connections will cause both to
fail until one power-cycles the switch and it re-learns the correct MAC
association with each port.

The problem doesn't occur with a hub, as a simple hub sends the same packets
to every port on it.

By way of testing, I'll suggest that you connect the desktop and then
power-cycle the modem, then on the desktop do an "ipconfig /renew" and see
if that fixes things.

*Always* check the "ipconfig /all" and "route print" settings before drawing
any conclusions about anything.
 
B

bill a

The patch cable I sent along with the desktop was a straight thru cable, and
we also tried the cable he had been using with the laptop, which I haven't
had a chance to look at, but I'm pretty sure he wouldn't have had a xover..
The laptop is WinXP, but I don't know where it is on SP's.
The power cycling idea sounds promising. I take it that a modem records the
MAC from whatever computer is first hooked up, and then expects that no
other MAC will be connected while the modem is powered up? I suppose in
normal usage, that wouldn't be problem.
I hope to get over to the guy's house in the next couple days. I already
told him to try the power cycling, which he may get to tomorrow.

Thanks Greg

Bill
 
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