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Comment by daveoc64 | Hacker News Reader

People make blanket statements like this without thinking of how it is used by popular consumer devices.

As others have said it's really necessary for some consumer devices to work properly - especially if you have more than one of the same device.

Games consoles are the best example.

If you have one console only, then you can usually forward ports manually, but if you have two or more of the same console, and want them to go online at the same time, then you need to use UPnP.

If you don't have UPnP enabled on one of the consoles, you'll see issues like being unable to join some games or being unable to do voice chat with certain players.

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> Games consoles are the best example.

Not with you there bud - we have multiple game consoles and my firewall doesn’t even support UPNP. I also have never set up and DNAT or ‘punched holes’ in it to Mae them work. They just do.

I have replied elsewhere about Xbox Live, but it's generally an impossibility (without advanced forwarding or UPnP) to have two consoles (of the same type - e.g. two Xbox One consoles or two Nintendo Switch consoles), connected to the internet, both able to access ALL online features, at the exact same time.

Out of the box on most consumer networks, you're going to be able to access things like the store, downloading updates etc.

To play with certain players on peer to peer games (which are less common these days) or have a voice chat with certain players, you will need to port forward (manually or with UPnP).

You either need to forward ports manually (which can obviously only be done to one console), or use UPnP. The Xbox One and later does have an option to manually ask it to use a different port on multiple consoles for some features (so that you can port forward separately to consoles), but I am unsure if that will solve all issues in such an environment.

Only one of the two sides needs UPnP, no?

This is not true based on my experience with multiple switches and xbox one consoles.

It does depend on the game. A P2P game like Call of Duty will have problems when played simultaneously on more than one console because the external port can not be shared.

What happens though is that another external port gets forwarded to 3074 instead.

3074 -> 3074

3075 -> 3074

3076 -> 3074 etc.

Its likely uPnP does this automatically as even uPnP won't be able to map multiple devices to the same external port but it does make the process convenient.

That’s not how NAT works though. It uses random ports, and there are no collisions, unless you have thousands of Xboxes behind a NAT. Also, remember that CGNAT is a thing, with hundreds of households( with dozens of game consoles) all behind a single IP address. Essentially, the people talking about game consoles not working are wrong.

That is how NAT works for connections opened from private network to the Internet. If the console needs to listen to a port, the NAT must be configured to forward the listened port to correct device. Multiple devices behind NAT can not listen to the same port, and this is where the forwarding of different ports on public IP to same port on different private IPs comes in.

The source port would be random and conmunication would ride on that established connection. An exposed port is not necessary for client initiated communication.

Yes, you're talking about a device behind NAT which initiates a connection to an external service.

However, we're talking about a service listening behind NAT (in this case Call of Duty on an Xbox at home) that needs to be listening for connections initiated by other Xboxes to establish a P2P connection. This is what port forwarding enables and this is what uPnP automates.

Why wouldn't they use a solution like https://samy.pl/pwnat/ this is a long solved problem that doesn't require uPnP.

Is it somehow better than uPnP?

Yes, CGNAT is causing a lot of issues not being able to host multiplayer games, as I've experienced myself (with PC games, though server-client ones, not peer to peer ones).

Anyway, these days, if you don't have an IPv6 /56, you don't have a real Internet connection.

That's not true, at least for xbox live. It's NAT punching will gladly use UPnP if available, but doesn't rely on it, even for multiple devices on the same public IP.

It's unlikely that you will have an "OPEN NAT" status on more than one console without UPnP at the same time.

Depending on the game you're playing, that may or may not be an issue.

It can stop you connecting to certain players in a peer to peer scenario.

It'll be fine. They'll be on two pretty arbitrary public ports, but it works just fine if you have a vaguely sane nat implementation in your router. That's the whole point of nat punching. And even if you have an incredibly broken nat implementation that won't accept UDP packets from other sources than the server you originally connected to, there's a fallback pathway at the first layer of that port 3074 protocol that bridges p2p messages through live's backend.

As another example, last time I checked WebRTC didn't use UPnP, but has all the same issues as a fundamentally P2P UDP protocol. They use STUN/ICE/TURN, live uses custom protocols filling the same niches.

This Xbox help article explains how having a "Moderate" or "Strict" NAT can affect you and how it can be solved:

https://support.xbox.com/en-GB/help/hardware-network/connect...

I don't think anything has fundamentally changed in this area since the days of the Xbox 360. Back then it was a PITA to get two or more consoles working properly without UPnP, and I can't see anything about the problem that would be different now.

Nintendo has a similar page:

https://www.nintendo.co.uk/Support/Nintendo-Switch/Troublesh...

So does Sony:

https://manuals.playstation.net/document/gb/ps4/settings/nw_...

I hate Sony for that page. I’ve helped multiple people with router issues who turned out to have forwarded all those ports from wan to their PlayStation (or it’s previous IP). Ofc it wasn’t the issue at hand, but horrible none the less.

How does it work with IPv6-only networks?

The last I looked on PS4, they expected you to use a particular port. I don't think there was a dynamic portion, just forward port X to the PS4. I could absolutely be wrong though, it's been a while.

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