The Internet package that I'm using allows up to two devices to be connected to the Internet at one time. One of those slots is taken up by the host computer and the other by someone else's device not related to what I'm doing.

If I were to connect a virtual machine to the Internet, would that count as a third device? Or would it just use the host's connection?

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    "The Internet package I'm using allows up to two devices to be connected to the Internet at one time." I have never heard of such a restriction and I'd be curious to learn how they implement it. Could you share which ISP this is? – Luc Jul 24 '17 at 6:02
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    You should ask your ISP about this. Only they will know their own mind. – Stig Hemmer Jul 24 '17 at 7:04
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    Is not the situation that the ISP's device (modem or whatever) does not perform NAT (network address translation) by default and the limitation to two devices is for the situation where the two devices would be assigned public IP addresses? --- Similar conditions could apply to a connection offered by UPC Czech Republic for example. – pabouk Jul 24 '17 at 8:30
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    You question can be interpreted in multiple ways: "Can my ISP detect it?" (in which case Darius' answer applies) or "Does it violate my ISPs Terms Of Service?" (which only your ISP can answer) or "If it violates my ISPs Termin Of Service, are those terms even legal?" (which only a lawyer and probably a case in court can answer). – Heinzi Jul 24 '17 at 8:42
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    You could just always plug in another router into their modem. That would count as a single device, yet allow other clients to connect to it for internet. – zzarzzur Jul 24 '17 at 19:47

Most ISP usually don't have visibility on the actual number of devices connected on your home because you are behind a router (that probably runs a NAT that assigns each of your home devices an internal IP).

As far as the ISP can see, there is only 1 connection (via your router) to the ISP. How many devices behind the router is usually not visible. Unless each devices have their own public IP (which is usually not the case).

If the ISP somehow has visibility of how many devices connected to the router and using this information to determine how many devices in your house - as long as your VM network is on NAT mode, it will be fine (as the connectivity is behind your host machine).

If you set it to Bridging mode (where the VM will have its own IP in the LAN) - it will be then detected as the 3rd device as the VM will need its own IP address on the LAN.

Edit (Credit to TheCatWhisperer):

It is incorrect to say that they cannot see how many devices you are using if you use your own router. Unless ALL your requests are encrypted, they can simply examine the user agent string sent in most requests. Whether they would actually go to this trouble or not, who knows.

  • Comments are not for extended discussion; this conversation has been moved to chat. – DavidPostill Jul 25 '17 at 17:48
  • iirc, ISPs in the US inspect the MAC address to determine the number of connected devices. I actually had a router in a previous work place which could fake the MAC address specifically to overcome this restriction. – Tsahi Asher Jul 26 '17 at 15:21
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    @TsahiAsher: Do ISPs even see MAC addresses behind a router? – user541686 Jul 26 '17 at 17:21
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    The user-agent sniffing approach would break even with legitimate usage - a lot of iOS apps who do HTTP traffic have their own user-agents, so there's no way they would be doing something like this as they'd get more false positives than anything else. – André Borie Jul 26 '17 at 18:17
  • @Mehrdad i believe they can, perhaps through the ARP protocol. – Tsahi Asher Jul 27 '17 at 10:58

I had a similar restriction (Fastweb Italy), it was enough to connect a router to the modem/router of the ISP. Make the router create its own NAT with its own pool of IPs.

Doing so the ISP will only see a single device connected.

To avoid problems when you need assistance from them, set the MAC address and the name of the router to the ones of one of your devices. Doing so they will not see the router but a computer.

  • Italian here. I am not sure those restrictions are legal in our country. Do you have a link about the terms and conditions that force you to use a maximum number of devices? – Andrea Lazzarotto Jul 25 '17 at 14:03
  • It happened several years ago, I think they removed this limitation already. It was just something set in the modem/router that limited the devices connected at the same time – Fez Vrasta Jul 25 '17 at 14:18
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    Gosh, that's outrageous. – Andrea Lazzarotto Jul 25 '17 at 16:53

It depends what they're looking at.

When you make web requests over HTTP (not HTTPS) your browser will send a "user-agent", identifying your platform and browser and browser version, this is how in the UK some of the mobile networks detect and warn if they detect tethering (which is against their terms). For this they will need to be doing Deep Packet Inspection (DPI).

The other way they may detect an additional device is if you typically use a Linux machine and then you start connecting to Windows Update and vice versa.

As others have mentioned if your ISP provides your router they may be able to work out what devices are connected but if it is your own router they will not be able to see LAN activity only that which goes out on to the Internet which will instead be masked by your router.

So specifically for whether your ISP has supplied a router and can detect activity on the LAN is the following:

Hypervisors typically offer 3 options for virtual machine connectivity.

  1. Bridged - which is where the OS will let it send commands over the network directly (i.e. device appears like another device directly plugged into your network)

  2. NAT - Shares the address of the host computer.

  3. Internal/Host - Doesn't communicate directly with the wider network you are connected to.

See also VirtualBox's manual for VirtualBox specific explanation although others may be different they typically offer similar functionality.

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    Wouldn't that false positive on some reasonably common privacy tricks? – not store bought dirt Jul 25 '17 at 20:58
  • Well on the mobile network example they're only expecting Android, iPhone or Windows Mobile.. Seeing a desktop user-agent (i.e. Windows 8.1 means the user must be tethering). The common privacy tricks might not involve fundamentally changing the platform part of the UA but even if they do It's difficult for us to know for sure how they enforce their policy... but these are the methods I'm aware of. – Matthew1471 Jul 28 '17 at 17:33
  • @Matthew1471 what if you use the "request desktop website" mode? It seems unreliable – Fez Vrasta Jul 29 '17 at 8:51
  • It's up to the network provider how they implement this. I couldn't comment. Even with the "desktop website" there may be some tell tale signs that it's still a mobile (i.e. a fictitious version number). – Matthew1471 Oct 20 '17 at 17:25

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