Weird network connection problem

[dee001]

GM, I have a cat 5 cable coming into this office and it connects to a Netgear switch then feeds a computer a large printer, the customer has been losing connection to the printer so I am troubleshooting this and getting some weird results. Now the cable that is coming into the office works but I can not locate the other end of the cable anywhere in this building, there are tons of wires in the ceiling and I have tried to tone the cable back to the switches with no luck, the customer does not know the cable layout in the building it looks like they have had a few techs over that have just run new cables anytime they have had a problem so I can't locate the other end of this cable. But the weird thing is if I connect this cable directly to their windows 10 workstation it works no problem but if I go through a switch it doesn't, also I thought it may have been a bad switch so I grab my spare switch out of the car and the same thing using my Linksys switch. Windows detects the connections but doesn't pick up an IP address but if I use that same cable from the switch to connect to my Chromebook I get right online no problem. I have used different cables with no luck still no connectivity when I go through either switch but the system works fine if I use the cable coming out the wall and connect it directly to the system. Any suggestions on what could be going on?

 

[SAFCasper]

Since it doesn't work when connecting a switch there might be a loop created somewhere and spanning-tree blocks the port. Sounds like a possibility from your description of unlabelled wires running everywhere. Perfect recipe for creating a loop.

Another possibility is one of the pairs is damaged in that cable. The devices that work are negotiating the connection down to 100Mb only using 2 pairs so the broken pair is avoided.

Realistically, until you find the other end of the cable this is going to be entirely guesswork. If you think it goes back to a switch, unplug everything from that switch then use your tone & probe as they don't work when the other end is terminated in a switch. That's unless you have a few thousand spare to buy a digital Fluke one.

 

[HCHTech]

What @SAFCasper says - Plus, can't toning a live wire potentially damage the switch on the other end? You might use an IP scanner to identify other devices, maybe you could find the switch that way if it is managed....log into it (probably still at default passwords), etc. Unlabeled piles of spaghetti are the worst!

That's why previous techs ran new lines - the offered two choices to the customer. For $800, I'll figure out this mess, or for $150, I'll run a new line. You choose. and you can guess which one they chose.

 

[SAFCasper]

Plus, can't toning a live wire potentially damage the switch on the other end?

Not sure about damage but with traditional analogue toners a switch will short the connection resulting in no tone being generated.

Digital toners resolve this but they don't come cheap.

 

[YeOldeStonecat]

Until you track down where this ethernet cable goes...you're only guessing.
There much be a router for this office...to provide an internet connection....you just have to hunt down and document <what's in between>.

You'd be surprised how many times you can find some old hub or switch....up in the ceiling somewhere...or down in a basement somewhere.

Walking in with a switch, plugging that cable into it..and your laptop into that switch too...would not create a loop. Although you see 2x laptops work, but two switches not work...it's just likely a wonky cable, weak connection...and you're seeing a 50/50 chance of it negotiating a link properly.

Time to really trace back that ethernet...stick your head up in the ceiling tiles and track it all the way back. Or basement.
SOMEwhere it comes out and leads to the router. Who knows what's in between.

If you can't replace cable...at least reterminate what you find. And take out old stuff...I hate when people leave abandoned cable behind.

Got an ethernet testing device good enough to give you distances? Like a Fluke? Can help sometimes help shorten your recon time.

 

[Markverhyden]

Angryipscanner is a great start for discovery. If you had a higher end tester, like a Fluke CableIQ you could have it blink the port. Old school toner don't work when plugged into a switch. Another option, though time consuming, is to take a picture of the switches to identify active ports. Then unplug it from the work station and look for the missing light.

You said multiple switches. What's the situation? If their managed then someone should be able to see the traffic from the work station.

 

[VISA MC]

Can you plop a static IP into the machine ans get internet access?

I don’t know the cause, but I have seen this more than once where whatever device is providing DHCP, for whatever reason was not providing DHCP to devices behind an unmanaged switch.

It’s the nickel solution to the dime problem but might at least get the user functional until the root cause is determined.

 

[DRPCNZ]

I'm picking you have a loop. What are the lights on the switch doing when you plug the cable in?