Author Topic: Phantom network device  (Read 119 times)

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Offline Raj

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Phantom network device
« on: June 30, 2020, 06:01:07 pm »
So I have almost 20m long Ethernet cable, that when I connect to the router, with the other end connected to nothing, makes the router's port connected light, light up...
How screwed  am I?
Do i need to pull that wire off of my wall and replace it?

I think it's either caused by stray capacitance buildup in the wire or because I accidentally landed a hammer blow onto it while tacking it onto the wall...but the internals looked fine when I stripped that section of wire to inspect it, But let's not jump to conclusions.

when it is connected, my router log randomly reports "LAN4 link up 100 mbps" and "LAN4 link down" in a random interval of 2-3 minutes
« Last Edit: July 01, 2020, 06:35:04 am by Raj »
 

Offline fordem

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Re: Phantom network device
« Reply #1 on: July 02, 2020, 12:42:44 am »
My suspicion would be that there is an intermittent short somewhere in that cable - the router is seeing a link pulse when it shouldn't - and yes, you'll need to replace it, just opening up the cable (as you did to inspect) will cause issues with cross talk.

I've done quite a few cabling jobs where cables are connected to the various switches, etc., with nothing at the other end except an empty wall jack and I've never had the port lights come on, I've also seen situations where with a defective cable, you get a link light at one end, but not the other, and that has been because one end is receiving a link pulse from the other side, but the other end is getting the one sent.

If you have access to a cable certifier you can check it, generally speaking - I don't think check for capacitance, they do check for continuity, correct wiremap, length, attenuation and cross talk in a couple of different places.
« Last Edit: July 02, 2020, 12:45:11 am by fordem »
 
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Offline Raj

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Re: Phantom network device
« Reply #2 on: July 02, 2020, 04:14:04 am »
Thanks...replacing it rightaway
 


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