Ethernet Question

regdog said:

Is there any reason why my computer will only talk to one ethernet cable and not others? I got a new cable with my new modem but my computer wouldn't talk to it, so I went back to the old one. I checked the cable on a different computer and it works fine.

Thanks

Click to expand...

Ethernet cables are made up of four (twisted) pairs of wires on the inside. Each little wire plays a role in network communications (this configuration is sometimes known as the pinout configuration). A lot of more modern Ethernet adapters can auto-configure themselves for a cable wired straight-through or crossover. But some cannot (or might have this disabled).

On the cable that works, place the two end connectors side by side and see if the left-to-right (or right-to-left) coloring of those little wires is identical. If so, that's a straight-through connection. You might instead find that the two connectors have mirror-image color combinations as you look from left to right or right to left. That's a crossover cable.

First thought, since the one cable works in another PC, is that the cables differ in this. One is straight-through and the other is crossover, and that your PC cannot autoconfigure for this.

Generally speaking, you connect a PC to a network device with a straight-through cable, while PC-to-PC connections use a crossover.

If you're curious, here's a pretty decent article on this.

Check that cable "pinout" configuration.

regdog said:

I checked the cables. The colors are the same on both.

Click to expand...

Okay, that makes 'em straight-through. That's basically the default.

One cable works with both computers you've tried, one cable only works with one computer...

Hmm...

Are both computers connected at the same time?

Okay, cable testers can be fairly inexpensive. Here's a link, for example. But if you're only going to use it once every few blue moons, it's probably easiest to just discard the malfunctioning cable. Besides, unless you want to buy a cable crimping kit, it's going to lead you to the same result: throw the bad cable away.

NOTE, though: While the cable is by far the most likely culprit here, there's a small chance it's the network adapter in the computer where that cable doesn't work.

At this point, I say toss the incooperative cable unless you want it on standby for the PC that it still works with.

Don't know about where you are, but my local Radio Shack has a cable tester they let folks use, just in case they can sell someone a new cable.

Also lets folks test the new cable before leaving the store.

I used to build all my own cables. Now I only do it for longer individual runs. (I really dislike making cables.)

regdog said:

No. I can hook them both up at the same time and did when I was checking the cables. The modem will take 4 computers.
I even bought another ethernet by the same manufacturer and nothing.

Click to expand...

Make sure that the port on the modem doesn't matter, that is, that the cable is bad.

Also, sometimes one port is "special." It may not be labeled, but it may be set a little apart from the others.

That said, a new cable is not going to break the bank and it's always good to have a spare.

Here are a couple of network troubleshooting tips that might help shed some light on the issue. (I will use generic IP addresses for the examples, substitute your own addresses). I will also list the steps in as plain English as possible, with the assumption you have not done this before, as I don't know what level of computer skills you have.

First round hook up the computer and your modem with the old working cable. Try these steps to make sure it all works as expected.

Click the windows button and in the box 'Search programs and files' type cmd then press the Enter key. A black window should open with white text.

Type ipconfig /all and press the enter key, you should then see a bunch of text telling you about your network connection.

Look for a line in the second block of text that start DHCP Enabled, it will be either yes or no, write this down somewhere, we may need it later.

Look for the line in the second block of text that starts IPv4 Address, then write down that number, it should be something like 192.168.0.2 (the last 2 sets of number may be different). Also write down the number for the line Default Gateway.

Type ping 192.168.0.2 (or the number you wrote down in the previous step for your IPv4 address) then press enter. This tests that your computer and network card can talk. You should see a bunch of text appear with 4 lines that say Reply from 192.168.... etc. If it doesn't post what it does say.

You should now try to do the same for the default gateway. type ping 192.168.0.1 (substituting the address you wrote down earlier). This tests that your computer and modem can talk. You should see a bunch of text appear with 4 lines that say Reply from 192.168.... etc. If it doesn't post what it does say.

Finally type ping www.google.com and press enter. This tests that your computer can talk to the Internet.

Now replace the Ethernet cable in your computer and modem, making sure to use the same port. Now type ipconfig /renew then press enter. If you get an error message, post it here.

Now redo the same tests. If you get the same results then you are connected to the Internet and everything is working, the issue lies somewhere else. If you get any of the problems below, we can work to fix it.

Firstly if your DHCP enabled is set to no, then these tests won't give us the info we need.

Ipconfig results, if you don't get an IPv4 address or it looks like then this 169.254.175.12 (last 2 sets of number will be different) then you computer can't reach the modem. Make sure the cable is inserted correctly in the port at each end and that if you have multiple network cards, you only have one ethernet cable plugged in. If your PC fails here, then we are going to need more info such as you modem make and model number and type of service (ADSL or cable)

First Ping test. If your PC fails the first ping test the fault could be with your network card.

Second Ping test. If this test fails then the fault is either in the cable, the modem port or the modem. Try a different port on the modem.

Third Ping test. If you get an unknown host error then the problem is with DNS try ping 173.194.41.82 and press enter. This is an address for Google, if you get the four ping replies, it indicates the error is with DNS. Let us know what happens and we can help.

It's almost 3am here so I'm off to bed, will check back tomorrow to see how you get on. Sorry for the long post folks, but that's computers for you.

There are more things it could be as well as being really unlucky and getting multiple faulty cables. Try these and post your results

Does your computer have a wireless connection?

regdog said:

I was okay until attached the new cable and got this message.


Once I went back to my old cable everything was fine

Click to expand...

I forgot to ask, regdog. What is the length of the cable? 6 ft? 10 ft?

Those are standard lengths. They come longer, but that's most likely. Which is it?

regdog said:

I was okay until attached the new cable and got this message.


Once I went back to my old cable everything was fine

Click to expand...

You might be getting that message about the wireless because the cable (or whatever) isn't working correctly, so it tries the wireless.

If you have an active wireless device, make sure you disable that.

From the error it looks like its having problems distinguishing between wired and wireless. Do you know how to disable the wireless by turning off the radio. Is your PC a desktop or laptop?