The difference is that your home router does not get a public IP on its WAN interface, but perhaps the non-publicly-routable 100.64.0.0/10 [1] with CG-NAT.
So if you don't have a public IP address, how exactly are you supposed to forward anything? What is the other end supposed to connect to as an IP address?
Yes...? I know that, but does that cause any issues in practice other than death of P2P?
> So if you don't have a public IP address, how exactly are you supposed to forward anything? What is the other end supposed to connect to as an IP address?
I already mentioned port forwarding because with something like CG-NAT, it is often not possible (or not allowed). But I am not aware of any issues that stem from this other than an inability for others to establish connections directly to you. In fact, my network has a public IPv4 without CG-NAT and yet I am already used to being unable to receive data other than back through a TCP stream. That is the entire reason reverse proxy tunnels (such as ngrok, etc.) exist.
Well:
> If you’re a gamer using PS5, Xbox, or PC in 2025, running into Double NAT or CGNAT port forwarding issues can make online play nearly impossible. Many 5G home internet and satellite services (like T-Mobile Home Internet and Starlink) put users behind carrier-grade NAT, which blocks direct connections and port forwarding. The good news? There are still workarounds that can open up your connection for smoother online gaming.
* https://www.modemguides.com/blogs/modemguides-blog/double-na...
See also:
* https://en.wikipedia.org/wiki/Carrier-grade_NAT#Disadvantage...
When we went from dial-up speeds to DSL/cable to fibre we were able to have all sorts new applications due to higher bandwidth. Smartphones are capable of all sorts of things because they're always online: back in the day people used to talk about "being online" and saying "sorry, I was offline", because you only had connectivity at the office or at home (where you dialed into your ISP).
What kind of applications and services are not being invented because we're stuck with the current non-P2P / centralized setup of IPv4+NAT?
I don't know? I've never had CG-NAT and yet I've never seen a piece of software that takes advantage of that except maybe for games that use UPnP to open ports.
Maybe we haven't seen many products available on the market to take advantage of it because the current standard of NATs make such things practically unworkable?
Its pretty much impossible to ship smart home stuff that is hosted locally (i.e. not without it connecting to some cloud service) because people want to access these smart devices from outside their home. They're not likely to configure a VPN to connect home, they're not going to configure NATs in any workable fashion (or may be unable to, such as CGNAT), the applications probably don't want to have to handle having NAT hairpinning issues, etc.
So instead we continue down everything that's popular being something that requires a cloud proxy/relay (because that's the only way things actually work for most people), when in reality if things could just be public we could do a whole bunch more and empower people to easily host things themselves.
Which, as a sibling comments mentions, is the point.
The fact that (CG-)NAT is in the way could be precluding the development of "software that takes advantage of that". It's a form of (negative/inverse) survivorship bias: kind of like zoning for only single-family homes and yet saying "no one wants mid-rise towers/apartments as evidenced by the fact no one building them". The current rules/structure/architecture preclude any other options.
Is there anything you do on a computer that involves communicating with another user? That's not just anything - that's most things! All communication between two computers is improved by not requiring NAT.
Corporations love to keep us dependent on their central servers, of course.
