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

 

[ChrisD.]

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

 

[bledd]

Not using any powerline adapters are you?

Only using 1 cable between each switch and device.

 

[Quartz]

Yes, check for fixed IP addresses.

 

[JollyJamma]

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.

 

[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?

 

[JollyJamma]

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

Not sure. It could be a chassis short (much like that which Gamers Nexus covered recently). Maybe try a different PSU?

I had a driver issue with a network adapter that was only fixable with a manual update of the driver from the manufacturers website. Doing a windows reinstall didn't help because it was an old driver being bundled in with the OS.

 

[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.

 

[ChrisD.]

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.

 

[bledd]

Could be a bad switch or cable.

 

[Quartz]

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.

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.

 

[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.

 

[ChrisD.]

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.

Very good point.

 

[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

 

[Quartz]

Have you checked the ports on your router? Sometimes particular ports are dedicated to particular functions. For example one port may actually be a WAN port or an isolated network segment exposed to the internet (I'm having a middle-aged moment as to the precise term). If you've plugged your office switch into one of those ports you may well have troubles.

 

[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.

 

[Quartz]

or an isolated network segment exposed to the internet (I'm having a middle-aged moment as to the precise term).

FWIW the term is DMZ - DeMilitarised Zone.

LAN drivers updated to use manufacturer's drivers,

Ooh - that PC doesn't have a 'Killer' NIC by any small chance? Those used to be sure-fire disaster areas, but my knowledge there is well out of date.

 

[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.