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Is it possible to connect two computers together that have WiFi enabled (but they aren't connected to any ISP like Comcast, Xfinity etc)?

For instance, if both computers are connected to a router but that router isn't connected to the public internet (but it still has an IP address) would it be possible for both computers to send packets across to each other if they knew the respective IP Addresses? Or do you always need an ISP to communicate to another computer.

I guess my question is can there really be a p2p network that's created outside of being reliant on an ISP/ For instance direct communication through WiFi or Bluetooth etc.

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Two computers on the same network that can reach each other, can always communicate using any and all protocols, which includes P2P.

The router is the connector of all the devices on the local network. If internet is available, it becomes the gateway to it. But in both cases, its behavior on the local network is exactly the same (firewalls permitting).

Although P2P might work in the local network without the internet, the possibilities are very limited. For example, programs that "call home" might not work if they don't support an offline mode. As another example, copying files directly between network shares will always be much faster than using P2P.

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  • You might want to reread your first paragraph and remove/modify it. I'm sure you did not convey your intent as I know you know about p2p trackers/DNS/finder services.
    – davidgo
    May 20, 2020 at 20:55
  • @davidgo: What did you find wrong with this paragraph? DNS is not a factor here as there is no DNS server, so computers communicate by IP addresses (most P2P programs already work this way). P2P trackers can be setup locally as well, although this is really too much work, but there is no indication that the software the poster wants needs them.
    – harrymc
    May 20, 2020 at 21:01
  • I think the any and all protocols part is overreach - the structures appropriate to making computers on an isolated LAN work are different to those of a p2p network. I agree that given the ability to get and run arbitrary code you can make a lan work on p2p technologies, but I don't think anyone would ever do this, save as to develop for a p2p network.
    – davidgo
    May 20, 2020 at 21:26
  • @davidgo: The LAN is really a mini-internet. The exact same API is used to connect to internet nodes as to local nodes, so there is no reason that what works over the internet won't work over the LAN, provided that the right infrastructure of programs is created.
    – harrymc
    May 21, 2020 at 6:10
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Yes, it's possible. That's actually how your LAN works the whole time. Packets within the same subnet are just directly relayed by the Wi-Fi access point (and/or by the Ethernet switch). They don't go through your ISP connection and don't rely on any of its services.

For that matter, packets within the same subnet don't even need a router – you could create a fully functional IP network by using a plain Ethernet switch, or by directly connecting the Ethernet ports of two PCs with a cable, then by manually setting up IP addresses. (But a router is still convenient to have for DHCP-based address assignment, even if it never really gets asked to route anything.)

(The only (small) influence that your ISP may even have on your network is address assignment. For example, in IPv6 it is traditional for the LAN to use addresses provided by the ISP. But that's not required – if your network doesn't connect to others, you can use any addresses you like.)


In fact, that's how the entire Internet works – it consists of many autonomous networks which just connect to each other in some way or another, but each of them internally has its own internal routing procedures.

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Computers can be connected in a LAN so they can communicate with each other without an Internet connection. (In fact was developed first, with Internet coming later).

When it comes to WIFI (at a basic level) you generally want a router to act as a central point, even if the router does not connect to the Internet. (There are other ways to do this but they are more complex).

A p2p network has a meaning different to the one implied in your post. A p2p network is a distributed network without a central point. There are a number of ways to do this without an ISP - and this can be done with WIFI (normally as a mesh setup). Bluetooth would typically be unsuitable as a p2p technology as its typically associated with point to point, rather then having multiple simultaneous connections as required for peer to peer networking.

An ISP is little more then a paid intermediary which connects networks together, ensuring connection to the established worldwide network. The technology used to create those links can (and historically mainly was) used for private networks - as the number of peers grew. (The Internet used to be distinct from an internet)

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