strange lan network issue?

Question

I am hardware technician last day i faced a strange lan network trouble never see before such an issue.
ok i wil expline it
there are 12 computers connected in a lan two switchs and one router modem connecting it each other. among this computer only one computer is in upstairs , a 35 mtr utp cable connected with this pc. and evrything working fine expect the pc in upstair. The pc in upstairs only sending bits not receiving signal so its not communicating with other pc's. At first i thought problem with the lan card so i change the lan card same problm was der. then i change the entire pc same problem this time agine. then i change the pc that time same problm exists . so plan to change switch and lan cable same problm remains at last i remove the cable (it was going through a 1/2 inch pvc pipe to upstairs) and i use the same cable to connect with other pc that time it works fine. when ever the cable go through the 1/2 inch pvc pipe to upstaires it doesent works so what may be the problem ? will any electric cable induction effect it (but it was working fine before few days until it get malfucntions last 1.5 years it was working fine)what happening here any one experienced ever ?

Answer 1

The problem is easy- whatever is connected to the upstairs cable will not be able to communicate to the LAN. Finding the solution will be a challenge. Some things to try are...



a) release and renew the IP address of the upstairs computer. If it isn't picking up a good IP address then it means it can't see your DHCP, which is the whole mischief right there. I will wager that you'll be getting the garbage 169.254.x.x IP address it comes up with when it can't find the DHCP.



b) find a shorter wire and use it to replace the wire going upstairs, and then plug a computer into this short wire, essentially replacing the upstairs computer with another downstairs computer. If it picks up a valid IP address then something is causing interference on the wire going upstairs (IEEE rules say ethernet cables need to be at least six inches away from any open power outlet due to electromagnetic intereference) If it still can't pick up a valid IP address then there's a problem with the switch it's plugged into that prevents it from seeing the DHCP server.



c) just to be sure, try to give the upstairs computer a static IP address and then see if it can connect to anythign on the LAN. If it can't then it's definitely a problem with the connection, and if it can, then the problem is with the DHCP. Are you sure the scope is large enough and has enough spare addresses to accomodate all the computers on that subnet?



I had a similar problem as this a number of years back. After tracing the wire I found the user had all on her own wrapped the spare length of ethernet wire around the computer's power strip to make it look neat. She might as well have cut the wire with scissors.

Answer 2

It could be a surge protector that may creating a problem, as other PC are working with switches and when you bring the same PC and connecting directly it works fine. Call the electrician and check the cable line in that area and if possible change the T-connector too.

Answer 3

The black magic of Ethernet wiring. If the cable is really long its possible that its picking something up. It's possible that in removing the cable from the wall you moved something on the connector. I'd try replacing the cable first and see if that gives different results. At minimum chop of the plugs or sockets and install new ones.

Answer 4

What does netstat -in say? Are there collisions? Output/input packets?



Cat cable is shielded, you can't induce interference. That being said, are you using

the correct Cat certified cable?