Keep losing network connectivity

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Keep losing network connectivity

Postby GeordieJedi » Sun Sep 24, 2017 7:07 pm

Hi there guys.

I'm experiencing a bit of an obscure problem, I keep (seemingly) randomly losing
network connecitvity on my PC's.

It is most apparent on my desktop PC. (Espcially if I am running it from a live
USB stick). This has been happening for a few months now, but getting progressivley
worse.

However this is just starting to affect my laptop too.

Normally a reboot or two (of the PC or laptop) will seem to resolve the issue for a little while.
But this is becoming more like 4/5/6 reboots in order to resolve the problem.
which is becoming quite frustrating.

My desktop and laptop are both hardwired via a switch. The modem / swtich / and cat cables
are all around 4-5 yrs old at this point.

My laptop sits on my computer desk, my desktop PC sits on a trolley next to my desk.
The cat cables are 5m in length, and its about 2.5m between the switch and the computers

I do move the trolley from time to time (to get that the plugs and what-not behind the
trolley), but there is a good amount of extra cable length, so there is no danger of
the cables being pulled out of the sockets in the switch.

I dont seem to get many dropouts when using wifi on my phone or tablet.


Troubleshooting -

1. I have re-seated the cat cables in all my devices (desktop, laptop, NAS)
2. Rebooted the (desktop, laptop, NAS)


This is leading me to think that I may have a dying swtich or dying ports on the switch.


Q1. Is there anything that I can check to determine where the issue lies ?
Q2. Am I missing anything ?
Q3. Am I best off just buying a new switch and or cat cables ?


Writing this out has just made me realise that I haven't powercycled the switch for
quite a while. (I will do this now).


Useful information:

My network set up is a follows -
Virgin media cable modem/router (downstairs)
Cat cable run upstairs to switch (upstairs in office)
PCs and NAS connected to switch (upstairs in office)

Modem:Virgin media Super hub 1
Switch:Linksys SE2500UK, 5-Port Gigabit Ethernet Switch


TIA for any help or advice.
GeordieJedi
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Re: Keep losing network connectivity

Postby guy » Mon Sep 25, 2017 7:16 am

Try swapping the modem-to-switch cable with one of the PC cables and see if that improves the other PC's connection.

Another thing to try (not at the same time) is swapping to different Ethernet ports.

Presumably your PC and laptop connect to the NAS, but phones etc do not? That might just affect the ones that use it, though I have little experience with remote file systems.

Also, don't rule out the Internet point of presence (PoP) at the exchange. It will be auto-configuring and sometimes they do things like giving priority to mobile traffic. Sometimes a bright idea can make them badly behaved for a while until the maintainers learn the error of their ways.
"We don't need no frikkin' aliens, we c'n do this ourselves!" — anon.
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Re: Keep losing network connectivity

Postby Dutch_Master » Mon Sep 25, 2017 10:33 am

Failing hardware is most certainly an option, but as Guy implicated, it could be anything in the chain. There's a reasonable chance it could be the network-part of your desktop and laptop, the switch or the router. The most likely chance is the switch, as you say the error doesn't affect mobile devices. Take the laptop downstairs and connect it directly to the cable modem. If that fixes the issue, purchase a new switch. If not, contact Virgin for a new modem/router.

HTH!
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Re: Keep losing network connectivity

Postby nelz » Mon Sep 25, 2017 5:06 pm

What do you mean by network connectivity? Is it just Internet connections that go down or are you also unable to contact computers on your LAN?

Does pinging IP addresses work, tricky faults like this can often be caused by DNS.
"Insanity: doing the same thing over and over again and expecting different results." (Albert Einstein)
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Re: Keep losing network connectivity

Postby GeordieJedi » Mon Sep 25, 2017 7:18 pm

Hi there guys. Thanks for the advice so far.

OK to answer your questions -

1. I seem to lose all network connectivity (both LAN & WAN)

2. I've just replicated the issue -

2.1. The desktop lost all network connectivity
I couldnt reach the internet, and I couldnt reach any other devices on my LAN
(I tried to ping both their hostnames and their IP addresses).

It failed. I got the following error message =
Code: Select all
connect: Network is unreachable


2.2. At the same time, the laptop was able to connect to both the LAN and the internet.
I could ping other devices on my LAN via hostnames or IP addresses.

2.3. Again at the same time, using my phone, I was able to connect to the modem/router
via Wi-Fi and was able to get online without any issues.


Q4. So does this mean that the problem is caused by either my connection to the switch
(cat cables), or the switch itself ?
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Re: Keep losing network connectivity

Postby nelz » Mon Sep 25, 2017 8:44 pm

If the desktop and laptop are both connected by cable, try switching the cables and the ports on the switch.

Also, try connecting the cables directly to the modem - the Virgin modem has 4 LAN ports.
"Insanity: doing the same thing over and over again and expecting different results." (Albert Einstein)
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Re: Keep losing network connectivity

Postby guy » Tue Sep 26, 2017 8:40 am

The fact that the desktop and laptop come and go independently, and the desktop is affected when booting from a different OS image (on a USB stick), suggests that this might actually be an issue with software configuration.

I have sometimes had problems when a mixed ecology of systems is present, for example some flavours of Windows used to grab control of your DNS given half a chance and muck up the connectivity of your Linux boxes. Similarly, if Linux got there first then the router would refuse to let the Win box make the grab, so it would sulk by failing to recognise the (embedded Linux) router's control of DNS. Even today, one busy machine that gets there first can hog the link and slow the others down so much that their connections break. What brand/s of mobile device get used over the WiFi? Do the periods of disconnection tend to come when there is lots of activity from (an)other device/s?

Don't stop the swapping-around experiments though, they will help to pin down the area of trouble.
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