Ethernet conundrum

In My Humble Opinion
1

(putting this in IMHO because of its diagnostic/opinion type nature, my apologies if it belongs elsewhere.)

I recently broke up with one of those scary boyfriends who knows a lot more about IT than I do and wasn’t afraid to use it. :rolleyes:

The day he left my friends’ house where he was living, the internet stopped working. So, the ISP guy came out, and said it looked like someone took a ball point pen to the ethernet port on the cable modem. He replaced the modem.

Now, it’s a a simple (wired) network, with PC-1 in the living room, PC-2 in another room, and a router. When the ISP guy left, PC-1 would go online, and PC-2 would not – I had plugged PC-1 directly into the cable modem for his convenience.

When I hooked everything back up the way it was and it didn’t work, I tried plugging PC-2 directly into the modem; that didn’t work, so finally I switched the ethernet card from the working PC into PC-2, because it gets used much more.

So now PC-2 is fine, the router is fine, but PC-1 will not get a connection. I have tried both the onboard ethernet port, and a replacement ethernet card, presumably working.

The router has 3 green lights – its power indicator, the “internet” light, and PC-2’s connection light. No light for PC-1 though it’s plugged in. I looked at the other ports; they all look undisturbed.

Of course I have reset the cable modem and router a few times; also I have gone into the router control program, changed the password, and made sure that it is set up for several addresses.

In addition, I tried plugging PC-1 into each of the four ports in the router (this includes the port that works for PC-2), and I went into the BIOS and disabled the onboard LAN when I put the new ethernet card in, in case of conflict. No dice.

I am stumped. Why would PC-1 go online just fine with the one ethernet card, but not another one, or its onboard LAN?

2

Your cable company records the mac address of the computer connected to it. You need to click start menu/run on the computer that works, and type ipconfig /all
Find a section called Physical address and write those numbers/letters down.
Go into your router configuration, and add that address under “MAC Address Cloning” or something similar. Unplug everything and plug it back in and it should all work.

3

Who is your ISP? Sometimes the DSL guys like to set you up so the login is happening on the PC not the router, making for some obnoxious behaviors under such circumstances.

If its a broadband provider like Cox or Comcast that is an odd puzzle.

MAC cloning would not explain one computer getting on through the router but not the other since the modem would still see the routers MAC address, this should leave you with no connection or both machines up.

4

Sounds like I should’ve mentioned the one thing I left out – when I tried to clone the router to PC-2’s MAC, everything stopped working. This is with the ethernet card from PC=1 installed.

I think that still means I should try jacobsta811’s suggestion. I’ll let you know. Gotta cook dinner first tho. Thanks!
P.S. It’s Comcast.

5

Roast in. Rice on. I was in the process of entering the physical address into the MAC cloning section of the router configuration when I realized that I recognized the MAC because it’s the same one I tried to clone before. However, maybe I didn’t unplug every single thing, so I’ll try anyway.

6

Have you checked the cable you are using ? If MAC cloning isn’t working or only still allowing PC2 on, and the connection light isn’t on I would tend to think you have some kind of hardware issue- bad cable, or bad NIC. It would be odd (but not impossible) for both the onboard and a PCI card to both be dead, unless you had some sort of power surge with them both plugged in. I guess make sure you are testing the onboard LAN without the PCI card in the computer at all, if a known good cable still isn’t getting a light at the router.

7

First off, based your indication that the link light on the router does not come on when one of the computers is connected, that indicates that the physical connection is faulty. That means a bad Ethernet cable, a bad NIC in the computer, or a bad switch port on the router. This is where you want to start looking.

I wouldn’t worry about trying to clone MAC addresses. Most ISPs, including Comcast, don’t filter access by MAC address anymore. Most of the time all you need to do is power cycle the cable modem when you change the device directly connected to it. Unset it on any devices where you tried to configure it. You don’t want duplicates on the internal network. Even if you were properly cloning MAC addresses in an appropriate situation, it would have no effect on only one LAN computer not being able to access the Internet. The ISP can only see the device directly connected to the cable modem - that is your router. If one computer on the LAN can access the Internet, it means it is correctly communicating with the router, which is correctly communicating with your ISP. Problems with additional computers, then, are between the computer and the router.

You need to get the network back to the way it was before you started fiddling with all the hardware. It’s easiest to start with all the power cords unplugged and computers shut down. Connect the Ethernet port on the cable modem to the WAN/Internet port on the router. Then connect the two computers to the LAN ports on the router. If your router doesn’t seem to have a separate set of LAN ports and a WAN/Internet port, you probably have a switch or hub instead of a router, in which case you need to get a router. Now plug in the cable modem and wait for the status lights to show that it’s connected. Then, plug in the router and wait for it to show that it’s connected. Finally, turn on the PCs. Verify that the computers obtain IP addresses from the router (valid ones will start with 192.168). Now we can start looking for problems.

Does computer 1 still not show a link light when connected to the router? In order, try a different port on the router, try a different cable, and try a different Ethernet card.