Network cable went belly-up

[bug]

So I have this network cable that's over 20m/66ft long that's mostly hidden from view via canals and furniture that decided it's was time to stop doing its job. I'm guessing there's an interruption somewhere, but I can't find it looking at the small portions of the cable that are still visible. Is there some sort of gadget that doesn't cost hundreds of $ that can detect where an interruption is located? I wouldn't need pinpoint accuracy, obviously, but enough to know where to unearth the cable and look. I'm hoping if it happened towards an end, I can just cut it and reattach the connector. I'm really not looking forward to replacing it altogether (it goes behind some shelves full of books).

TIA

 

[Bill_Bright]

None that I know of - unless you are willing to spend a fortune. There are wire trackers, but you almost have to be on top of the wire across its whole length. That won't solve your issue with the cable running behind bookshelves. The problem is, current doesn't just run up to a break (open) then stop. Current flows through a "circuit" - a word that implies a "closed" loop. If there is an open anywhere, current stops everywhere.

I will note that network cables don't just stop working. The cable (or one of the connectors) must have been damaged, perhaps through crushing (from walking on it, or setting heavy furniture on it), or being yanked/tripped over one too many times. Teething puppy dawgs are common culprits. And sadly, so is rodential and hungry 6 and 8 legged critters.

I recommend you verify it really is the cable first. Did you try a different port on the router? They can suddenly go bad. You can temporarily disconnect the old cable, run a replacement cable out in the open between the two ends, then connect the temp/new cable to the same ports to see if your distant device now works. That would, at least, verify the old cable is bad (or good).

Better yet, get yourself a decent Ethernet cable tester. As you can see, they are not very expensive. Anyone who builds their own Ethernet cables should have one of these. They also help prevent high blood pressure events and slow down radical hair loss and receding hairlines.

If you find the cable is bad, I recommend you try to use the existing cable to pull the new cable through. Before connecting new connectors to the new cable, snip off the connector from the old cable. Then, with really sticky tape (like Gorilla Super Glue Tape or Scotch Super-Hold Tape), overlap several inches of old and new cable and wrap the cables as tight as possible with the tape - trying not to make the temporary splice too fat or it will get hung up behind your bookshelves. Then try to pull the old cable out, pulling the new cable in at the same time.

Your other alternative is wifi.

Good luck.

 

[ShiBDiB]

Unexposed network cables don't typically just fail without an outside influence.

 

[bug]

@Bill_Bright Short of a replacement cable (kinda hard to get one that's 20m+ long) I have tried everything and I'm 100% sure it's the cable. The cable itself is well-protected (if it was accessible I would just be able to look at it/feel it), but it goes one story up so it has a few bends, which I guess are potential points of failure.
I am currently using WiFi as a fallback, but I don't like how it prefers to connect to the 2.4GHz band, because that always has better signal. Even if, in a straight line, my PC is like 6m away from the router, through a wooden floor.

@ShiBDiB Normally yes, but I could be in the lucky few % that got a cable with some hidden defects. Or maybe the tension around one bend may have been working against it all along. Another possibility is that it has failed at one of the connector, but the failure is just invisible to the naked eye. I guess I could try to re-attach the connectors, see if that fixes it.

 

[TheLostSwede]

Some motherboards have built in network testing utilities in the BIOS/UEFI.

Unexposed network cables don't typically just fail without an outside influence.

Actually, some seem to do. I've had several short-ish cables (1-2 meters) just stop working on me. No idea why, as they weren't touched.

 

[Bill_Bright]

Short of a replacement cable (kinda hard to get one that's 20m+ long)

Another reason to make your own. If you need a 17ft cable, you can make one instead of buying a 25ft cable. If you need a 10 inch cable to go from your modem to your router, you can make one instead of buying a 3 or 6 foot cable. I always make my own. I can make it length I want. Plus, with my tester, I can make sure it is good before using it. I note factory made cables are rarely, if ever, quality tested before they leave the factory.

but I don't like how it prefers to connect to the 2.4GHz band, because that always has better signal.

??? Afraid that does not make sense. A device should connect to the band with the better signal. If you meant you would rather it connect to the 5GHz band, then that is for short distances. 6m may qualify as short, but much also depends on other factors, like nearby sources of interference and obstacles like metal pipes and wires in the barriers (walls, ceilings, floors), or large metal objects like file cabinets and refrigerators causing RF reflections and/or barriers.

I have tried everything and I'm 100% sure it's the cable.

Then not sure the point of trying to locate the point of damage. You want a straight, one-piece run. You cannot cut out the bad section and splice in a new without significantly degrading total continuity. If there is a bad spot in the cable (other than a connector), you need to replace the whole cable.

Crimps (tight bends around corners) can cause problems. Pinch points (perhaps along baseboards) can too.

(if it was accessible I would just be able to look at it/feel it)

Do not assume that. Crush points can easily cause shorts or opens and not be visible or detectable by touch/feel.

 

[AsRock]

buzzer and a battery on the other end and check the cable that way ?, but that would depend on if you have the tools to add new connectors or if you have a soldering iron to take of a connector of a old unused board for the cable to plug in too.

But like bill says, better with a new cable as it be better to have no breaks in it.

 

[bug]

Another reason to make your own. If you need a 17ft cable, you can make one instead of buying a 25ft cable. If you need a 10 inch cable to go from your modem to your router, you can make one instead of buying a 3 or 6 foot cable. I always make my own. I can make it length I want. Plus, with my tester, I can make sure it is good before using it. I note factory made cables are rarely, if ever, quality tested before they leave the factory.

This isn't a matter of making vs buying, it's about whether I can avoid to replace the whole cable.

??? Afraid that does not make sense. A device should connect to the band with the better signal. If you meant you would rather it connect to the 5GHz band, then that is for short distances. 6m may qualify as short, but much also depends on other factors, like nearby sources of interference and obstacles like metal pipes and wires in the barriers (walls, ceilings, floors), or large metal objects like file cabinets and refrigerators causing RF reflections and/or barriers.

5GHz has more bandwidth and good enough signal. As you have noted, the router isn't that far. But since 5GHz always attenuates faster than 2.4GHz, the PC tends to prefer the 2.4GHz band

Then not sure the point of trying to locate the point of damage. You want a straight, one-piece run. You cannot cut out the bad section and splice in a new without significantly degrading total continuity. If there is a bad spot in the cable (other than a connector), you need to replace the whole cable.

Like I said, I was hoping I could get away with just snipping a little at one end of the other.

Crimps (tight bends around corners) can cause problems. Pinch points (perhaps along baseboards) can too.

Do not assume that. Crush points can easily cause shorts or opens and not be visible or detectable by touch/feel.

I know that. Once again, I was speaking in the event I would have gotten lucky and could easily spot the damage. But the original question was about a device that would look for a flaw I wouldn't be able to spot myself. You kinda dashed that hope, but I already had a feeling if such a device existed, it wouldn't be cheap.

Some motherboards have built in network testing utilities in the BIOS/UEFI.

Mine doesn't. Even if it did, I doubt it would be able to detect where the fault lies. Which is what I need, I already know the cable is bad.

 

[cvaldes]

I was hoping I could get away with just snipping a little at one end of the other.

You could try. After all, the connection is already kaput, you won't hurt it anymore.

Network cables can fail without any hint of damage. Physical damage undetectable to the naked eye as described by others before -- is one possibility.

Another distinct possibility is a failure where the connector plugs are. These are inserted into devices that often generate a certain amount of heat. Over time, the wires in the cable expand and contract due to temperature changes.

This is not limited to low voltage wiring like Ethernet cables. The same phenomenon happens in the wiring in your house's walls.

As mentioned before, network administrators build their own cables and use a testing device to verify signal integrity. While building your own cables isn't difficult, it's really something that is more consistently done by someone who does it frequently, just like soldering, changing your car's spark plugs, baking wedding cakes, knitting, whatever.

If you do acquiring the crimping tools, connectors, and testing gear, it would be wise to practice on a couple of short cables before trying this on your long one. I built network cables 25 years ago. However I didn't keep doing it. After ten years, I got rid of the tools since I hadn't used them and there was little chance of me doing so again. It's a skill that needs to be practiced regularly to maintain proficiency, a detail that is frequently missed by some commenters in this Q&A forum.

Best of luck.

 

[Solaris17]

Im Afraid bills right. Though I do understand its frustrating. You can try the ends if you want and see if it fixes it, but there is a good change it wont unless you know of something that is interacting with the connectors frequently (unplugging/plugging in) or maybe corrosion if you are near the water.

Otherwise if its replacement time (and it sounds like it is) like Bill mentioned, use the old cable to pull the new one. If its not that simple for you, then next time might I recommend just going to a hardware store and buying a few segments of pvc and making this easier on yourself in the future?

It may seem like a lot of work because it might take some extra hours to secure and work with pipe, but here you are without a working cable for potentially days.

 

[Calenhad]

This isn't a matter of making vs buying, it's about whether I can avoid to replace the whole cable.


5GHz has more bandwidth and good enough signal. As you have noted, the router isn't that far. But since 5GHz always attenuates faster than 2.4GHz, the PC tends to prefer the 2.4GHz band


Like I said, I was hoping I could get away with just snipping a little at one end of the other.


I know that. Once again, I was speaking in the event I would have gotten lucky and could easily spot the damage. But the original question was about a device that would look for a flaw I wouldn't be able to spot myself. You kinda dashed that hope, but I already had a feeling if such a device existed, it wouldn't be cheap.


Mine doesn't. Even if it did, I doubt it would be able to detect where the fault lies. Which is what I need, I already know the cable is bad.

You can set your wifi network card to prioritise 5GHz (should be in the settings for the adapter in device manager).

If your cable have no connection at all, not just degraded performance, it most likely have to be replaced. Because you need all 4 wire pairs for 1+Gbit connection, but only one pair for 100Mbit. Network equipment will usually sync 100Mbit as long as any one of the 4 pairs are intact. But some (usually older) equipment will only fallback if the middle pair is intact. So, unless you luck out and the break is at one end in whatever extra length you have there, the cable have to be replaced. The only way to test if that is the case, is to cut the cable and attach a new connector and test if it works then. (If you know what you're doing you can measure the bare wires instead)

You can buy a cheap continuity tester for network cables, but that will only tell you if there is a connection or not. Measuring the cable to located a short is a much more complex task, and probably more expensive than even hiring a professional to replace the cable. I used to do this kind of work, measuring copper lines for a telco. But that was on a different scale. Much easier to see difference in capacitance over kilometers than meters.

 

[Frick]

When I find myself in these situations I use it as an excuse to refurnish the place, or at least do a really deep cleaning. 20m of CAT6 is cheap, at least if you crimp your own connectors.

 

[Shrek]

This isn't a matter of making vs buying, it's about whether I can avoid to replace the whole cable.

I'd take a flat head screwdriver and push each blade in; that may fix a bad connection.

 

[ir_cow]

Unexposed network cables don't typically just fail without an outside influence.

You would be surprised how many I replaced in the ceiling at the news station. Either I would splice the line if it was cat5 and found a kink. or just replace the whole thing for Cat6a.

After finding the bad section and stripping the outer layer, nothing seems to be wrong. All wires intact, but one pair will have a pinch in it usually. Came from the factory that way.

Much more common failure point was the ends. I would replace the server sides all the time. Something about the bend / weight over time makes it fail.

 

[Lost_Troll]

Is there some sort of gadget that doesn't cost hundreds of $ that can detect where an interruption is located?

The cheap testers will only tell you what pairs are open.

When you buy patch cables and install them like a CMR riser cable, they will always break if they are the cheap no name ones. Get a good quality patch cable from Monoprice to replace it if you do not have the tools or the time to make the replacement with CMR riser cable.

If you are in the US, Lowes has a nice Southwire network tool kit for 36$ and tester for 32$.

When I did my house, I used Monoprice spool of 250FT CAT 6 Riser cable and a similar feed through RJ45 jack.

 

[Fangio1951]

hi Bug,

I've been making my own cables for around 35 years and always buy a 100 metre roll as it's a lot cheaper by the roll.

That way you can make your own cables whenever you want/need.

One thing to be aware off is - there are two different types of RJ45 connectors, depending on the type of cable being used.

One type of connector has straight pins for stranded cable (patch leads) and the other has bent pins for use with solid cable (structured cabling).

And definitely get a cable tester = takes the guess work out of the equation.

 

[ir_cow]

Just avoid buying Copper Clad (CC) cables. They aren't really copper wires. Good luck getting 25ft out of them.

 

[1freedude]

I'm with Frick. Use this as an opportunity to deep clean behind the scenes. Go look at my latest post in nasty rotten filthy. I was pulling cables to uncover that mess. And, I was gonna say this earlier...try to find a new route if new connectors dont fix it. Might end up being shorter.

And, @Fangio1951 I came across a new-to-me connector that staggered the wires...the odd four were in line, and the even four were just above. We used a comb thingy to align them into the termination. Not sure of the reasoning, or benefit. And, I never tried to insert the wires without the comb.

 

[freeagent]

I just replaced 50 feet of Cat5 with 30 feet of Cat7 for like 15 bucks. Probably not helpful.. in my case it was

 

[cvaldes]

It's not cost effective to buy a crimper, a bag of connectors and a cable tester for a one-off job. I will reiterate that this is a simple enough job for an experienced person (tinkerer, professional IT staffer, PC store owner) who regularly does this.

Does it make sense for some newb to buy a stand mixer, cake pans, whisk, baking sheets, silicone mats, pastry bags and tips for a one-off special occasion cake? NO.

This is a repeated theme at PC/tech forums like this Q&A forum (and other tech-related sites). I don't know why PC nerds seem so resolute in suggesting impractical approaches. This really only happens on PC/tech sites, no where else.

No one on a cooking site is going to tell you to bake your sister's wedding cake. Great, I can make good pâte à choux batter for excellent profiteroles. That doesn't make me a pastry chef. And even with my experience I might get a less-than-perfect first batch because I haven't made these for years. And I'm certainly not going to suggest to anyone who has never baked before to make their own and expect professional grade results.

I guarantee that if you have never used a stand mixer you will soon spray ingredients all over your kitchen counter because you don't know what you are doing. At least you can eat a misshapen profiterole. You can't do anything with a botched network cable. No one picks up a cable crimper and starts pumping out flawless network cables.

If you are going to toss the crimper and cable tester into a cabinet the moment you turn the router on, forget it. It's a good skill to have if you're regularly doing this type of work but it's not something you can put on your resume.

Just pay someone to install a new custom length network cable the correct way or do it yourself with off-the-shelf cabling.

 

[Jacky_BEL]

Some motherboards have built in network testing utilities in the BIOS/UEFI.

Motherboards with Marvell network onboard can have this testing feature.

2.9 Virtual Cable Tester® Feature
The 88E3015/88E3018 devices Virtual Cable Tester (VCT™) feature uses Time Domain Reflectometry (TDR) to
determine the quality of the cables, connectors, and terminations. Some of the possible problems that can be
diagnosed include opens, shorts, cable impedance mismatch, bad connectors, termination mismatch, and bad
magnetics.
The 88E3015/88E3018 devices transmit a signal of known amplitude (+1V) down each of the two pairs of an
attached cable. It will conduct the cable diagnostic test on each pair, testing the TX and RX pairs sequentially. The
transmitted signal will continue down the cable until it reflects off of a cable imperfection. The magnitude of the
reflection and the time it takes for the reflection to come back are shown in the VCT registers 26.12:8, 26.7:0,
27.12:8, and 27.7:0 respectively.
Using the information from the VCT Registers 26 and 27, the distance to the problem location and the type of
problem can be determined. For example, the time it takes for the reflection to come back, can be converted to
distance using the cable fault distance trend line tables in Figure 11. The polarity and magnitude of the reflection
together with the distance will indicate the type of discontinuity. For example, a +1V reflection will indicate an open
close to the PHY and a -1V reflection will indicate a short close to the PHY.
When the cable diagnostic feature is activated by setting Register 26.15 bit to one, a pre-determined amount of
time elapses before a test pulse is transmitted. This is to ensure that the link partner loses link, so that it stops
sending 100BASE-TX idles or 10 Mbit data packets. This is necessary to be able to perform the TDR test. The
TDR test can be performed either when there is no link partner or when the link partner is Auto-Negotiating or
sending 10 Mbit idle link pulses. If the 88E3015/88E3018 devices receive a continuous signal for 125 ms, it will
declare test failure because it cannot start the TDR test. In the test fail case, the received data is not valid. The
results of the test are also summarized in Register 26.14:13 and 27.14:13.
11 = Test fail (The TDR test could not be run for reasons explained above)
00 = Valid test, normal cable (no short or open in cable)
10 = Valid test, open in cable (Impedance > 333 ohms)
01 = Valid test, short in cable (Impedance < 33 ohms)
The definition for shorts and opens is arbitrary and the user can define it anyway they desire using the information
in the VCT registers. The impedance mismatch at the location of the discontinuity could also be calculated know-
ing the magnitude of the reflection. Refer to the App Note "Virtual Cable Tester® -- How to use TDR results" for
details.

 

[A Computer Guy]

Some motherboards have built in network testing utilities in the BIOS/UEFI.


Actually, some seem to do. I've had several short-ish cables (1-2 meters) just stop working on me. No idea why, as they weren't touched.

Some managed network switches also have testing utilities.

 

[Shrek]

I've had several short-ish cables (1-2 meters) just stop working on me. No idea why, as they weren't touched.

Oxidation of the blade to copper connection?

 

[TheLostSwede]

Motherboards with Marvell network onboard can have this testing feature.

I've had that on Intel and Realtek chips as well.

Oxidation of the blade to copper connection?

Nah, they were just not transmitting data any longer. Tried cleaning, using with different devices etc. Cheap cables I guess.

Some managed network switches also have testing utilities.

Right, yes, my Netgear switch does, but it's somewhat limited. Forgot about that.

 

[The_Enigma]

Short of a replacement cable (kinda hard to get one that's 20m+ long) I have tried everything and I'm 100% sure it's the cable.

You can get a shielded Cat6A from Monoprice in 75ft length for $34. Or a Cable Matters brand on Amazon of the same thing for $25.

I would also suggest having a Klein Tools VDV501-851 around to do cable testing for situations like this where you don't know the problem and think you are sure you narrowed it down to the cable. A tool like that is an easy way to check a cable first and verify it is fully functional.
It does measure cable length too, but not in a really accurate and professional capacity and I don't think it will tell you the distance to a break, but it is still a great tool to have to verify cables. The cheapest devices to more accurately measure the distance to a break would be from NetAlly, but they are expensive for the home user who only checks things like this once a year on average