Return to

Unreliable ethernet connections


Hey All,

I’ve started a new job as the IT administrator (the only person of the team) and I am now in charge of a network that is horribly unreliable. It seems like the previous IT person had a bad crimper that didn’t properly seat the pins into the wires. Also I have noticed that it looks like it’s the type of connector that is supposed to be used for stranded cable, not solid cable. Either way, I have devices connected through ethernet that can sit there pinging a device over and over again, and randomly have timeouts returned. I’m about ready to order a bunch of connectors and recrimp the ends of all the cables I can, and see if the problems go away. Any input on if the cable connectors could be the issue, or other possible causes of random timeouts when pinging over ethernet? Thanks.



Bad routing and VLAN setups can do that… but that depends on your network being mildly complex. If you have simplified the test case to “known working laptop on one end of the cable” and “known working tester on the other end” then that definitely points to a bad cable.

I’ve experienced weird LAN traffic behaviour with managed switches that had been on for a few months/years and which were running low on RAM due to an obscure memory leak. Rebooting the switches (temporarily) solved the problem.

Then there’s the situation where the Ethernet cables have been run too close (and parallel to) the AC power lines leading to devices like airconditioners, fridges and microwaves… resulting in signal corruption when the devices kick in.



If you know for a fact many crimps are buggered start there, quicker you get known goods the better.

1 Like


@level1 Thanks for the input. The network I inherited does have way more vlans than I’m used to working with. I might try to simplify it down to Phones, Internal and Guest VLANs and see if that fixes some of the issues. I’ll probably go and re-crimp ends as I can as well, just so I know that they are done right and well. Thanks for the input.

1 Like


What are the purpose of the current VLAN’s? Define their purpose, scale down as necessary but it sounds like re-crimping is certainly going to be in order.



There is separate VLANs for Workstations, Servers, Internal Wireless, Guest Wifi, Phones, and I think a few more that I can’t remember. I think that just having Internal Network (Wired and Wireless), Guest wifi, and Phones are all that are really needed. I don’t quite see the reason for splitting up the internal network so servers and workstations and wireless internal devices are on separate VLANs.



Excuse me. Why the F did you stop at pinging stuff? If you’re a net admin, you should have access to you switches. I can’t really understand why aren’t you checking port stats instead of fantasizing about recrimping everything. Sure, it’ll make you look busy, but it’s retarded.

Edit: apparently, the above statement is “abrasive”. Let me elaborate. I’m not saying you’re a retard. I’m saying that the idea of jumping into action on a hunch is retarded. The fact that some pings sometime get dropped doesn’t really account for much. I’m not a network (traditional, anyway) admin, and even I know qos-policies and rate-limits exist, and often used to limit ICMP throughput. Before running around with crimpers or shuffling cables around, check if there actually is a problem. Port stats and logs provided by your network switches are the very first thing you should check. Maybe you’ll find actual port errors, maybe not. Maybe it will be some faulty sfp. Maybe your network is just congested to the point where ICMP packets get dropped by qos. Maybe it’s some other random shit like misconfigured etherchannel somewhere. But using your head should be prioritized over using your legs. Collect the info, analyze it, and only then act. At the very least you’ll find which links are bad instead of recabling the whole network (which, I’m pretty sure, business owner wouldn’t be happy about).

1 Like


VLANs for Storage, Servers, Clients, Wireless, Phones, and Printers isn’t uncommon. I would get a cable tester and verify which cables are good, but only after making sure there’s no issues with the switch configs. If you don’t have one already, I’d create a network diagram of how each switch is supposed to connect to each other before hunting down cables



Lots of good advice in this thread. I just want to touch on crimping, and punching.

If the previous tech fucked up crimping, they probably fucked up punch downs too. You’re going to have your work cut out for you re-punching the patch panel, and the wall connectors. Don’t add to your own misery by crimping the short patch cables. Just buy a boatload of 1-3ft patch cables and be done with it.

Honestly, if the patch cables all look like they’ve been custom crimped, I’d probably start by replacing those with off-the-shelf patch cables. Like, I probably wouldn’t even test them. I would just play the odds that whoever crimped them eventually got tired of the process and tried to finish up as fast as possible.



2c, But it is not worth screwing around. Buy pre-made 3m patch cables for the field outlet users, buy 1, 2 and 3 m cable for the patch panel.

Fucking around building cables to length (badly) is a waste of your time; unless there really is nothing to do at that place, you have more important shit to be doing.

From the sounds of it the existing cabling is at least partly buggered and done by someone who doesn’t know what they’re doing. i’d (at least) replace dodgy cables as you find them with problem reports. As per @Levitance, if they look sus i wouldn’t even waste the time to test (chances are you don’t have a fluke tester anyway - those LED testers are pretty useless - they won’t show a whole heap of issues - there is more to it than simple continuity testing - they may have been ok back in the days of 10 or 100Mb but not gig+).

If there are still problems between A and B when there are known good cables all the way through start looking at switch error counts, etc.

Dont forget cable length can be an issue. If there are custom cables everywhere they have have been to go further than 3-5m from the field outlet (and a user may have moved a 10m cable from one port to another) and that may be outside of ethernet max 100m spec (i believe it is typically max of 90m from panel to field outlet to allow 3-5m cable either end of the run only).

I’m not a cable guy, but mates with a few of them… i leave it to them. As a sysadmin i have more important things to be doing than fucking up making custom ethernet cables.

1 Like


Amateur here, but I have built/run/snaked cat5 and installed receptacles in several small/medium offices. While I encountered a bad crimp job that would pass some intermittent data possibly 2wice, by far the majority either worked, or did not. Perhaps just my limited perspective, but my gut says: test a few of the cables through known worrking ports - and be prepared look elsewhere if they are functional.



get in the ceiling and have a look. if the connections are fucked, it is possible the cables that were run may also have issues. ideally every cable up there is secured and is a solid cable not multiple cables patched together but i have seen cat 6 cables connected by these guys in ceilings before and low and behold the connection was crap. you may also have damaged cables or cables that are too long and the connection is degrading.

1 Like


If you’re going to go to that extent (investigating/replacing infrastructure cabling), i’d suggest getting an actual cable technican with a fluke.

As a sysadmin with no proper equipment you are wasting your time. A fluke will indicate which cables are dodgy, where the break is, what type of break it is, any interference, etc.

As a sysadmin, you have Windows 7 to replace, windows 10 roll outs to do, RIDL/Spectre/meltdown to patch, etc. etc.

You can do those things properly, you can’t do cabling/cable-testing properly in any sort of reasonable time frame without the skills and equipment. Pick your battles… time is limited.


Home? Run your own cables all you want. Work? You’re on the clock. While you’re screwing around half-assing cable testing, you could/should be doing a lot of other things.

Do your layer 3, layer 2 troubleshooting, but if it looks like layer 1 (cables), and you’ve replaced the patch cables… get a pro with the tools required to do it. He/she will give you far better results, in a lot less time.

1 Like


Perhaps the other folx on this thread are more knowledgeable or specialized in what they do than I am. However cable testers are cheaper than humans testers and also work tirelessly and indefinitely. I think OP can test their own cables if they see fit.



A decent cable tester is a couple of grand…



it depends on the job. my job we do everything from wiring to cellphone repair to web design to security systems. some places you have one narrow job description and everything inbetween.