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The issue is letting untrusted or badly behaved devices on the network. UPnP works great, if you control which devices get on your network. Static port forward

The issue is letting untrusted or badly behaved devices on the network. UPnP works great, if you control which devices get on your network. Static port forwarding combined with DHCP gets annoying quickly, you end up having to set up static assignments for every device that may need a port forwarded, which can be a lot, with modern multiplayer gaming and p2p. And for applications that select a random port on startup, such as some bittorrent clients, you either have to manually forward the port every time or select a static port. UPnP serves a purpose and is extremely convenient, as long as you trust the devices on your network.

lostlogin 6y ago
> And for applications that select a random port on startup, such as some bittorrent clients, you either have to manually forward the port every time or select a static port. What if you run them over a VPN? I don’t use torrents much but have a client containerised with OpenVPN. I’m not a networking expert but I had assumed (with all the dangers that comes with) that this moved the problem to the VPN provider?
- mercora 6y ago
  it will work as long as you are the one initiating the connection. if some peer suspects you have a wanted piece available i.e. from another peer in the swarm it can not communicate the intent to get that piece from you to your client directly. i think BitTorrent can relay messages through intermediate peers to make your client establish the connection to that other peer (reversing the initiator). Otherwise peers will exchange other peers that are visible to them so that your client might eventually learn how the other peer that wanted that piece is reachable and connects to it. So it actually will work without port forwarding but reaching your client will be harder and thus less peers inside the swarm will be available to you or them, likely making it slower.
daniellarusso 6y ago
So, keeping track of which device on your network belongs to which MAC address, and reserving an address for each, is that what you mean by ‘annoying’ - the administration of that?
- KozmoNau7 6y ago
  That's the easy part. Plenty of applications (such as bittorrent clients) use randomized ports. So you have to either disable that, manually add the port forward every time you start the client, or let UPnP handle it, because you don't let any untrusted devices or apps onto your network. And multiple devices on the network may need the same port forwarded at different times, such as multiple games consoles.

lostlogin 6y ago

> And for applications that select a random port on startup, such as some bittorrent clients, you either have to manually forward the port every time or select a static port. What if you run them over a VPN? I don’t use torrents much but have a client containerised with OpenVPN. I’m not a networking expert but I had assumed (with all the dangers that comes with) that this moved the problem to the VPN provider?

mercora 6y ago
it will work as long as you are the one initiating the connection. if some peer suspects you have a wanted piece available i.e. from another peer in the swarm it can not communicate the intent to get that piece from you to your client directly. i think BitTorrent can relay messages through intermediate peers to make your client establish the connection to that other peer (reversing the initiator). Otherwise peers will exchange other peers that are visible to them so that your client might eventually learn how the other peer that wanted that piece is reachable and connects to it. So it actually will work without port forwarding but reaching your client will be harder and thus less peers inside the swarm will be available to you or them, likely making it slower.

daniellarusso 6y ago

So, keeping track of which device on your network belongs to which MAC address, and reserving an address for each, is that what you mean by ‘annoying’ - the administration of that?

KozmoNau7 6y ago
That's the easy part. Plenty of applications (such as bittorrent clients) use randomized ports. So you have to either disable that, manually add the port forward every time you start the client, or let UPnP handle it, because you don't let any untrusted devices or apps onto your network. And multiple devices on the network may need the same port forwarded at different times, such as multiple games consoles.