JohnH said:
The cable modem has one outlet. I unplug the desktop and plug it into
the laptop with the same configuration + firewall off but it wont
connect to the internet.
Any suggestions?
Thanks
John
There are two kinds of Ethernet cables. "straight Thru"
and "Crossover" cables.
http://en.wikipedia.org/wiki/Ethernet_crossover_cable
A Crossover cable, is used when you connect two computers
directly to one another. The Crossover cable connects the
TX of the first computer, to the RX of the second computer.
It also connects the RX of the first computer, to the TX of
the second computer.
The Straight Thru cable works, when the computer and the
"other box" have opposite wiring on their jacks. Then the
proper TX-RX and RX-TX connection gets made, without any
crossing of the wires being needed.
So when an Ethernet connection doesn't work, you read
the instructions to see if the cable type is mentioned
in the user manual, with respect to connecting a computer
to the box. It may tell you whether a crossover cable is
needed or not.
There are cases where the cable type doesn't matter. If
the computer has a "gigabit" or GbE or 1000BT network
interface on it, they usually come with MDI/MDIX capability.
The interface figures out where the TX and RX are, and
automatically corrects things for you. My current computer
has that on it, so I never have to worry about the cable.
As it is, I keep one cable of both types close by, for any
emergency. My "Crossover" cable has a red connector on one
end, and a blue connector on the other end. Implying the two
ends are "not the same". That is how I can tell what I did with
my Crossover cable, by checking the colors. A "Straight Thru"
cable will likely have same colored connectors on both ends
of the cable.
The next step, is debugging. How can you tell if there is
something on the other end of the cable ?
Some Ethernet NICs have a test capability. Marvell GbE
NICs have a cable tester, and that gives a confirmation
that all the wires are making electrical connections. When
I first got this computer, I had to use that, to find one
of the contacts on the connector was dirty. Not every
computer has that, so we move on to the next test.
If you open a "Command Prompt" window, that window
accepts DOS commands. A useful command is the "ping" command.
For example, I know the address of my router box. My computer
connects to the router. The router manual tells me the
default address of the router is xxx.xxx.xxx.xxx, which is
an IP address. To see if I can reach the router, I go to the
Command Prompt window, and enter the command
ping xxx.xxx.xxx.xxx (where the x's are the IP address)
If the ping returns a response, then I know I'm connected
to the other device. The rest of your problems, are then
higher layer (protocols and rules and the like).
If there is no response, either the cable is bad, or the
cable is the wrong type. I reach for my trusty "alternate cable"
and try it, repeating the ping command.
Other useful commands for the "Command Prompt" window:
ipconfig (shows your network address)
ipconfig /renew (renew DHCP lease)
nslookup
www.microsoft.com (DNS lookup test - returns IP address)
(May also mention which DNS server used)
One tiny issue with cable modems, is the MAC address. The MAC address is
a physical layer address, and it is supposed to be unique. The cable
modem may have taken note of the MAC address, and that may be preventing
the laptop from using it. The second article mentions "cloning" a MAC
address - that would be the process of assigning the same MAC address
to your laptop, as your desktop used. In general, such a practice
is not really that bright (like when you next try to connect the
laptop directly to the desktop
), so if you do that, place a
sticker on the computers, noting the fact you've been messing
around with the MAC. Record the original MAC on the sticky label,
so you can later restore it. It will help someone unravel what you've
done, later.
http://en.wikipedia.org/wiki/Mac_address
"Cable MODEM "Married" to an Ethernet MAC Address"
http://www.duxcw.com/faq/ics/cablemac.htm
A search like this may dig up more info on the cloning process,
if you figure that is what is holding you back. I've never
had to do this myself. On one of my computers, the cloning
function is actually supported on the BIOS flashing tool,
but that is the exception rather than the rule.
http://www.altavista.com/web/results?q=cloning+mac+address
This is one reason, it is nice to connect a router to the
cable modem, from day one. The cable modem "marries" the
MAC address of the router, and you can plug any old computer
into the router and get your connection to the Internet.
At least, until the day comes, that the router dies...
Good luck,
Paul
