How can two home networks interfere with one another?

StewartR

StewartR

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My neighbour just popped round to ask me an IT question. He's concerned that his home network seems very sluggish from time to time, and he thought it could be due to "interference" from our computers, and he wondered whether there was anything we could do to prevent it.

I wasn't sure I understood quite what he meant - he's in his late 70s and he admits he doesn't really understand a lot of modern technology - so he went to get his laptop, and opened up Windows Explorer. And there, in the 'Network' section, he could see lots of our devices - our desktop PC, our broadband router, our printer, even our Sonos player. I couldn't believe it. So I went to my desktop PC, opened up Windows Explorer, and in the 'Network' section I could see his laptop and his Panasonic Smart TV.

I wouldn't have thought this was even theoretically possible, but then networking knowledge is a long way away from being my strong suit. Could anyone explain [1] how it could have happened, and [2] how we could prevent it?
 
neil_g said:
either one of you is connected to the others wifi (ever done any testing?) or do either of you have powerline adapters?
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Our wifi is password protected and they don't know the password.
Their wifi is password protected and we don't know the password.
We use powerline adapters but they don't.

Does that help?
 
In theory your power line adapters shouldn't be accessible from their house, but if something is wired wrong that could be the problem, but I think for now you can probably rule that out.

Try turning the power line adapter off and see if it still happens. Do any of your power line adapters have wifi which perhaps you have not protected?
 
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neil_g said:
that makes absolutely no sense then.

somehow one of you is connected to the others, otherwise you would not see the others devices..
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That's what I thought.

I didn't test whether or not we could actually access one another's devices, but I thought that even seeing them on the network should be impossible.

Any other suggestions?
 
ecoleman said:
In theory your power line adopters shouldn't be accessible from their house, but if something is wired wrong that could be the problem.
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thats what i was thinking, if both use powerline but theres some odd electrical connection between the properties.

only other thing i can think is there is some sort of odd ad-hoc network going on that is open.
 
Are your Powerline adapters secured? - out of the box they have *separate* security to the router.

He's hooked into your system (if he can see your router) and the Powerline is the weakest point in the chain from your description. Unplug the Powerlines and see what happens.
 
ecoleman said:
In theory your power line adapters shouldn't be accessible from their house
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You're assuming dumb Powerline adapters.

If they're wifi repeater Powerlines the situation is very different.
 
I had exactly the same thing at my house.

I never bothered to look for a reason, just changed the IP range and wireless channel that my router was pushing out. Problem solved.
 
Alastair said:
Are your Powerline adapters secured? - out of the box they have *separate* security to the router.

He's hooked into your system (if he can see your router) and the Powerline is the weakest point in the chain from your description. Unplug the Powerlines and see what happens.
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OK, I can try that.

But even if my powerline adapters are unsecured, how might that be relevant? He's not using them.

Also, with my powerline adapters disconnected I can't use my PC on the network so I can't test whether or not his PC and hisTV are still on the network.
 
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ecoleman said:
Do any of your power line adapters have wifi which perhaps you have not protected?
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Alastair said:
You're assuming dumb Powerline adapters.

If they're wifi repeater Powerlines the situation is very different.
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None of my powerline adapters has wifi capability.

Broadband router connected to TPLink TL-PA211
TV set top box connected to TPLink TL-PA4010
Desktop PC connected to TPLink TL-PA211

I've checked the specs and none of them has wifi.
www.tp-link.com/en/products/details/cat-18_TL-PA211.html
www.tp-link.com/en/products/details/cat-18_TL-PA4010.html
 
Very odd. They also use secure pairing so your neighbour would have to pair with your to access your network.

Does your router have a DHCP list of devices? If so Can you see any of his devices listed?
 
Alastair said:
Unplug the Powerlines and see what happens.
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The other issue with this is that the problem seems to be intermittent.

Our neighbour brought his laptop round with Windows Explorer running, and it had a list of our devices showing on it. I pressed F5 (refresh) and they all disappeared, leaving just his devices. But then I went to my PC, opened up Windows Explorer, and I could see his devices.

Diagnosing intermittent problems is always prone to false positives. So I'd really like to understand why we think unplugging the powerline adapters might solve it, even theoretically, before trying it.
 
StewartR said:
The other issue with this is that the problem seems to be intermittent.

Our neighbour brought his laptop round with Windows Explorer running, and it had a list of our devices showing on it. I pressed F5 (refresh) and they all disappeared, leaving just his devices. But then I went to my PC, opened up Windows Explorer, and I could see his devices.

Diagnosing intermittent problems is always prone to false positives. So I'd really like to understand why we think unplugging the powerline adapters might solve it, even theoretically, before trying it.
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A process of elimination.
There are three ways he can access your network. Ethernet cable directly to your router, wifi or your power line adapter.

As you say e doesn't know your wifi password and we assume he hasn't run an Ethernet cable to your router, the power line adapters would be the obvious choice.
 
However as you say it's intermittent, it could be a wifi connection with a poor signal.

Do you have an iPad or iPhone? If so download an app called FING. It will scan your network and list all the devices.
 
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If he's not using powerline adapters and yours don't do wifi then unplugging yours can make no difference.

Neil's idea of an ad-hoc connection being established is the only thing I can think of without having physical access to run tests. I've not seen a wireless device in ad-hoc mode in yonks though, and have no idea if it could be used to establish a bridge.
 
ecoleman said:
Does your router have a DHCP list of devices? If so Can you see any of his devices listed?
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I don't know. As I said, I don't know very much about networking.

My router is a Technicolor TG582n, When I log in to the admin interface, one of the panels on the screen is 'Home Network' and it lists a number of devices. Some of them have names which I recognise and some are just gobbledygook (eg 'Unknown-c0-a0-bb-1c-6b-38'). Some of the names which I recognise are our devices; some of them are devices owned by other people (eg our home automation installer) which have previously connected to our network; and some of them are devices owned by our neighbours.

I know it's not a list of current connections because some of the devices listed belong to people who are currently well outside wifi range. So it appears to be a list of all the devices which are connected or have historically connected to our network, possibly in the last [N] days/weeks/months or possibly in all time. But I don't know what I can do with this information.
 
ecoleman said:
Do you have an iPad or iPhone? If so download an app called FING. It will scan your network and list all the devices.
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FING is also available on Android, it seems. I'll give it a whirl.
 
ecoleman said:
Do you have an iPad or iPhone? If so download an app called FING. It will scan your network and list all the devices.
Click to expand...
OK, I've done that. It lists 13 devices, most of which I recognise and none of which is obviously our neighbour's.
 
ecoleman said:
You obviously didn't get as far as my second paragraph then.
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Sorry, missed that one.

From what you've said Stewart, it has to be a wifi signal a wired connection is very unlikely. Possibly some device on your network repeating the wifi back out. That can be narrowed down though, as far as I'm aware wifi is either received or sent but not both from most devices. What have you got wired into the system? - either directly or via a wired connection to the Powerlines. If your PC is wired by the Powerline but has a wifi card, disable the wifi card in settings. Same with any other PCs or laptops wired into the network.

You should be able to see what devices are active, not just those that have been active, on the router control panel page. There should be no devices you can't identify - but it may take a while to work your way around things. You need to work through that list.
 
I wonder if there is something in the "home automation" that you just mentioned. I might suspect a device that has a wired and wireless adapter bridging between both your neighbour and your networks. I would check what devices you have wired in your house to rule this out (like a laptop in a docking station maybe?). It does seem very odd though :)
 
StewartR said:
OK, I've done that. It lists 13 devices, most of which I recognise and none of which is obviously our neighbour's.
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Here's the list of devices as shown by our router. Don't worry if you can't read the tiny print, that doesn't matter. What does matter is that I've highlighted the ones which I recognise.

As you can see, our devices have made both wired and wifi connections, as expected. Devices owned by other people who have been allowed to connect have all been via wifi, as expected. But our neighbours' devices are all via wired connections, if I'm interpreting this correctly. Even their laptop, which I can identify here and which they connect to their home network via wifi.

This suggests to me that our wifi is not a problem, and that the connection between our network and our neighbour's network is not via our wifi. Anyone agree/disagree?

15384-1463407587-5c1f3d94d0b4a2ce6e3b75efb3ffd058.jpg
 
J Veitch said:
I wonder if there is something in the "home automation" that you just mentioned.
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It's an intriguing thought, and something I wondered about, but I don't think so. Our house has recently been undergoing some renovation, and part of that included installing a Loxone home automation server. But that was only commissioned on April 23rd, and our neighbour says that he's been able to see our devices on his network for much longer than that - since before Christmas at least. I quizzed him very closely about that, because I wondered if the Loxone might somehow be causing the problem, but he was very very certain that the issue has been occurring for much longer than a month. So I think that rules out the Loxone server.
 
An iPhone/Surface Pro is unlikely to be connecting over a wired link. Even if it is listed under "Ethernet".

It looks like something wired into your system is repeating it's own WiFi hotspot.

Start by matching all of your devices to the list. I'd personally be barring from the network all the stuff you've already highlighted in red. And then anything I couldn't match to a known device in the house.
 
The fact they're listed as wired does point the finger at the powerline adaptors.

Then what Alistair said. It's easy enough to bar devices - you might as well solve the real problem and then look for the cause later.
 
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Phil V said:
The fact they're listed as wired does point the finger at the powerline adaptors.
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I would normally agree, but, if the neighbour doesn't have powerline adapters and Stewart's don't do wifi the physical layer that allows it to work is absent.
 
onomatopoeia said:
I would normally agree, but, if the neighbour doesn't have powerline adapters and Stewart's don't do wifi the physical layer that allows it to work is absent.
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Unless something wired into a Powerline is rebroadcasting the network from it's onboard wifi signal. You can create a hotspot from a phone, or a laptop,or a desktop.

Or if the home automation system is wired into the router but communicating via wifi with its components you have the usual situation for a screw-up with a smart device that's smarter than the operator/installer. Dumb home FTW.

According the posted screenshot there are no known devices of the neighbours communicating with the router by direct wifi suggests that the router security itself is ok (it's not a password issue). But that a compromise has been introduced by something added to the system. The easy way is to remove devices from the system until the problem goes away, then you have your suspect device.
 
Alastair said:
You should be able to see what devices are active, not just those that have been active, on the router control panel page. There should be no devices you can't identify - but it may take a while to work your way around things. You need to work through that list.
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OK, done that. Here are the results.

Active via wifi:
* SonosZP - We have a Sonos player, so that's probably it, even though it's not currently playing
* Unknown-00-40-9d-62-28-93 - No idea what this is
* android-4c77f05502143597 - Could be my phone or my Android tablet
* kindle-639c00d36 - Odd; we have two Kindles but they're both in airline mode (I checked)
* android-9a14bafc45053c41 - Could be my phone or my Android tablet
* EPSON0S6594 - Our Epson printer

Active via Ethernet:
* STEWIRIS-8 - Our desktop PC
* Loxone - Our home automation server
* Unknown-00-21-ed-20-2b-2d - No idea

So an interesting mix of the expected and the unexpected. What does this tell me?

15386-1463409041-11d07ae209deec38d372acee12423617.jpg
 
Are you sure he doesn't use powerline adapters? Would he know what they are? Do you know how his smart TV is connected to the internet wired/wireless? Could his Router be a AdHoc connection from your wireless device/router?

Do you have an older house that would share a ring main or earth with next door?
 
All your neighbours devices show as coming from your wired port. I would go and unplug each of the wired devices (maybe just the ethernet cable at the router ports?) until you can no longer see your neighbours devices, then you will know which one is bridging your wired network to their wireless network.
 
Alastair said:
SWhat have you got wired into the system? - either directly or via a wired connection to the Powerlines. If your PC is wired by the Powerline but has a wifi card, disable the wifi card in settings. Same with any other PCs or laptops wired into the network.
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OK. Wired into the system:

Technicolor TG582n router - obviously has wifi, but it's secured
Desktop PC - doesn't have a wifi card
TV set top box - no wifi capability
Loxone server - has wifi capability to allow use with controller app

The Loxone server is connected to various switches and devices throughout the house. It uses Cat5 cabling, but I understand that the control circuits are not connected to the home network - it just used Cat5/RJ45 because that's so convenient. Even if it were connected to the home network, all the downstream devices are definitely dumb (eg light switch) so there's no way they could be responsible for any security breaches.

The list of active devices I posted shows three which are wired. Two of these are the desktop PC an the Loxone. I don't know what the third one is. I think the TV set top box is 'HUMAX' on the list, which is currently inactive. The STB is currently in standby mode, though I don't know whether that means it's inactive on the network.

Are we getting anywhere?
 
Alastair said:
I'd personally be barring from the network all the stuff you've already highlighted in red. And then anything I couldn't match to a known device in the house.
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Phil V said:
what Alistair said. It's easy enough to bar devices - you might as well solve the real problem and then look for the cause later.
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Does that solve the problem though? The problem is that our devices show up on our neighbour's network. How does barring his devices from our network solve that?
 
Did you read what I wrote above?


That's exactly what was happening in my network. Next door was BT and I'm Virgin.

I suspect that the two routers formed their own wireless connection with my router acting as a relay for the BT one.

Once again, the fix is:

Change your DHCP IP range from the default one and change your WiFi channel from auto to a fixed one, preferably at least 2 to 3 channels away from your neighbours.

And yes, we had hard wired, PoE adapters and wireless running.
 
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J Veitch said:
All your neighbours devices show as coming from your wired port. I would go and unplug each of the wired devices (maybe just the ethernet cable at the router ports?) until you can no longer see your neighbours devices, then you will know which one is bridging your wired network to their wireless network.
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Good suggestion. However I cannot see any of his devices on our network at present. It is an intermittent problem. Unplugging things and seeing what has happened is not an efficient means of solving it - albeit it might be the only means if we can't come up with anything better.
 
admirable said:
Do you have an older house that would share a ring main or earth with next door?
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Do they need to be on the same ring main (unlikely) or just on the same phase? Some years ago, my parents and their neighbour used one of the old fashioned intercoms that communicated through the mains. These were supposed to be for internal communication in a single house but because the 2 houses were at the end of the line, they were on the same phase and worked between the houses.
 
I'd expect the Humax to be the TV box, as it's a brand associated with this.

Is the Loxone purely a hardwired system? - I wondered if many of the "unknown" devices could be connected. If you switch it off, how many drop off the active list? There are four "unknown" devices with labels that follow the same pattern as the rest on the wireless section of the list - any remote controls or remote sensors?
 
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