Help please :) Intermittent network issue

[iostream]

Hello,

Wondering if someone can provide some advice, as I am running out of ideas. I'm having trouble as the problem is intermittent.

My simple home network is illustrated below:

Router -> gigabit switch (office) -> 3x PCs
Router -> gigabit switch (living room) -> NAS, AVR, Nvidia Shield, BluRay player
Router -> Raspberry Pi running PiHole
Phones etc are on WiFi, and I have no problems here.

Diagram in spoiler below:

Spoiler

The above setup has been in place for 3+ years without issue. Last month the problems began, and the culprit seems to be when my wife turns on her PC in the office. A few minutes go by, and then all Ethernet-connected devices lose connection, both to the internet and the LAN.

I work from home, and everything is rock solid all day every day until after dinner when her PC gets turned on, and down goes the network. HOWEVER - this doesn't happen consistenly. Sometimes a couple days go by and everything is fine. Sometimes the issue appears multiple times per night.

The current fix is to reboot the switch in the office, and then our PCs are back online a few seconds later.

Things I have tried:

• new Ethernet cable between the wife's PC and the office switch. Problem persists
• new gigabit switch in the office and in the living room. Problem persists
• new motherboard in the wife's PC (thought the NIC may be at fault). Problem persists (also upgraded her from W10 to W11 as I've been meaning to, but the problem still persists)
• moved DHCP server from the Raspberry Pi back to the router. Problem persists
• changed router back to ISP provided router. Problem persists, so I have resumed using my Netgear RAX120 router
• installed manufacturer's LAN drivers on wife's PC (as opposed to bundled Windows drivers). Problem persists.
• editing DCHP reservation pool so that my assigned IPs / leases are outside of this range. Problem persists.

Things I have not tried:

• new Ethernet cable between the office and the router (current one is under the floor boards, marked as 'B' in the diagram). I have trouble seeing how this cable is at fault though, as the network is rock solid until my wife's machine comes online
• running Ethernet directly from wife's PC to router
• factory resetting the router - although I find this unlikely to fix anything, as changing the router did not help either
• test each cable with an Ethernet tester kit

For the time being I have disconnected her Ethernet cable and am using a USB WiFi adapter, and now the network is stable. While this is fine, I'd of course prefer to have the machine hard wired, hence this request for input.

Sorry for the long post! Figured more detail was better than not enough.
Cheers

 

[iostream]

Have you checked that her IP isn't conflicting with something on the network such as the router?

Yeah I've had a look a few times when it occurs - no conflicts from what I can tell.

Not using any powerline adapters are you?

Only using 1 cable between each switch and device.

No powerline adapters, just direct Ethernet. And there's only 1 cable to each switch, and from there 1 to each device if that's what you mean.

Yes, check for fixed IP addresses.

So I have two fixed IP addresses, but these have been assigned within the router admin console. i.e. it shouldn't then try to give that fixed IP out to another device.
I could however assign a fixed one for my wife's machine to see if that helps.

 

[iostream]

Can you try a different LAN adapter?

Update drivers of the LAN adapter?

Deffo check the cable.

I’d also make sure that there isn’t a short that’s sending power down the LAN cable.

I've changed her motherboard in case it was the NIC / Ethernet port that was causing issues, but this didn't resolve the issue sadly.
Also did a clean install of W11 - I just used Windows Update for the bulk of the drivers, but I'll certainly go to the motherboard's driver website and try the LAN drivers from there. Will give that a go today, thanks.

And yes, eventually I'll need to run a new cable between the office switch and the router to see if it is the culprit - but it never plays up until her machine is on.

How would I go about checking for a short / power being sent down the cable?

 

[iostream]

I do actually have a spare PSU here, I will give that a go over the weekend.
Hmm and looks like a tenner will get me an "ethernet cable tester" from the Rainforest, I'll pick one of those up too.

Let's see how the manufacturer's drivers work out first.

 

[iostream]

Have you swapped out the switch from the office with the one in the living room, to rule out an issue with it? Or bypass it and run your wife's PC directly into your router.

I replaced both the office and living room switches, I'll update my post to include this. Sadly still having issues. But yes good idea, I'll also try running a cable direct from her PC to the router for a couple days to see if it crops up again.

 

[iostream]

What you set on the router console is called a DHCP reservation. You should make sure that those reservations are outside the pool of assignable addresses. For example you might have a pool of DHCP addresses going from 192.168.1.10 to 192.168.1.100 so your reservations might be 192.168.1.201 and 202.

Something else: on your wife's computer go into the properties and advanced properties of the TCPIP v4 protocol and check that everything is blank or set to DHCP or default.

Good advice, thank you - I will look at the DCHP reservation range tonight, but I am 99% sure my "static" assigned ones are within the pool of assignable addresses, i.e. something for me to fix.

Had a quick peek over lunch at TCP/IP v4 settings - both IP address and DNS are set to "obtain automatically", so everything is blank.

 

[iostream]

A lunchtime doodle, if if simplifies my wordy opening post:

Spoiler

 

[iostream]

I'm lucky with FTTP, so that uses up the WAN port on the router (just double checked).
Thanks for the suggestion though!

LAN drivers updated to use manufacturer's drivers, so will be testing that tonight along with editing the DCHP range.

 

[iostream]

She's got an 'MSI X570 Gaming Plus', spec page says 'Realtek 8111H Gigabit LAN Controller', so I think I'm safe from the almighty Killer NICs....although my work laptop (Dell XPS 13 9305) does have a 'Killer WiFi 6 adapter' - but this is turned off as I am wired via a dock that has Ethernet.

 

[iostream]

It might be a long shot, but what happens if you unplug the network cable from your wife's PC and then turn it on?
I had a faulty monitor power supply many years ago that put out so much noise over the mains that it knocked out the ADSL connection, but only while the power supply was 'warming up' as the monitor came out of standby.

Interesting! I worry it will be something wild like this that has cropped up. However sometimes an hour or two can go by after she boots up before the network goes down, so it isn't during boot up.

 

[iostream]

Definitely check this as Mac flapping on the switches can bring the network down.

Alright, DHCP reservation range is now updated to be between 192.168.1.2 and 192.168.1.180.
Both of the reserved IPs are in the 192.168.1.19x range.

Shall report back tomorrow.

 

[iostream]

Remember to do an IPCONFIG /RELEASE and IPCONFIG /RENEW on both PCs with reservations.

The two reservations I have are on the Raspberry Pi (so I can remote in and update PiHole etc) and on a Windows 10 NUC that serves as my network storage / Plex server etc.

Before your post I've remoted into each and rebooted them, and I can see from the router admin panel that they have the expected IP addresses.

Does my reboot achieve the same as the IPCONFIG /RELEASE and IPCONFIG /RENEW?

 

[iostream]

Well, all was well for a week, thought it was solved!
Network down again twice tonight. As usual, rebooting the office switch solves it (temporarily anyways).

My Ethernet testing tool has arrived, so I shall test all the cables next.

 

[iostream]

Sorry for the thread necro, but wanted to post in case someone stumbles across this in the future.

I THINK the problem is either my work laptop (Dell XPS 13 9305) or the Dell dock (WD19TB). The laptop is running Windows 11. I noticed that when I put the laptop to sleep after work instead of shutting down, my problems arise. Seems while it is in sleep mode, it's still doing things, I can often hear the fan running etc. I don't think that in itself is a problem, but that's when the network appears to go down.

Anyways my solution has been a smart plug in the wall socket that powers the dock and laptop. I have it scheduled to cut power when my work day finishes. So now it doesn't matter if the laptop is sleeping or shut down, the dock has no power (and therefore isn't sending traffic via Ethernet).

Seems odd, but that's been in place for about 6 weeks now and I've not had a single issue. So in theory, issue resolved.

 

[iostream]

Looks like there is one 'payload' that has a new version (see below). Running the update now, thanks for the link.

Spoiler

 

[iostream]

Not really fixed though is it?
It's one of two devices and you have to fully turn them off to stop the issue. It's going to eat away at you until you sort it!

So when one of those devices is in standby, it's doing something funky and polluting your network with weird packets possibly. Surely, just eliminate the dock by not using it and then try putting the laptop in standby and see if the issue persists? I thought you said it was your wife's machine anyway or did I miss something?

EDIT: Can you only get ethernet via the dock?

Haha true, although I've largely forgotten about it seeing as it's been an error free 6 weeks
But yes, as per your edit I can only get ethernet via the dock, the laptop only has USB C for IO.

Everything is fine until the following combination - laptop is in sleep mode (and powered via dock) and wife's PC is in use. So I guess there is some sort of conflict. It's fine though if the laptop is either on or off, just not sleep. And sometimes an hour or two goes by before the network goes down - I'm guessing it goes down when the laptop comes out of "sleep" to do Windows updates etc.

 

[iostream]

There may also be a setting in your laptop BIOS that determines whether the dock passes through the MAC address of your laptop or uses its own, try changing the setting to whatever it isn't set to at the moment.

Ah interesting, good idea. I shall take a peek at the BIOS, thanks.

 

[iostream]

@Caged - found the setting, it is currently set to pass through the MAC address. Unfortunately 99% of the BIOS settings are greyed out, looks like I need an admin password from my work's IT department.

Spoiler

 

[iostream]

Good question. Ok I've checked MAC on the laptop, dock sticker and wife's machine - none of them match sadly.
Truth be told I'm ok with the scheduled power off switch for the laptop / dock, not only does it save a bit of power throughout the night, I don't need to listen to the fan every now and again when it's supposed to be sleeping. And of course so far, it has 'solved' the problem.

Although I'm happy to keep troubleshooting as suggestions and questions come in