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?
>other
Well you just handwaved away the most significant difference between NAT and native IP, obviously there won't be any major difference to discuss about anymore!
No, we can't ignore port forwarding. The key thing to realize about NAT is that someone owns the NAT. Back then, the NAT lived inside each of the home routers, so even if you have a "strict" NAT (endpoint-dependent mapping NAT, i.e. one that doesn't allow for hole-punching), you can easily bypass it by setting up a manual port forwarding entry.
With CGNAT that's no longer possible, you do not control the NAT. If your ISP decides to screw you over, you essentially do not have a choice but to get a relay, which needlessly costs you money.
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But if you really want to know what advantages native IP has over NAT, I'd say the lack of keepalive packets (to keep a holepunched NAT entry from being removed) is a pretty nice thing.
Port forwarding is nice, but everyone already knows you can hardly run a server at home (even in countries where port forwarding is standard). It's been this way for as long as I can remember. So yes I handwave it away because it doesn't matter. If that's the only drawback to CG-NAT (other than single IP address bans applying to entire nations or something) I hardly understand why it warrants treatment as such a terrible awful disaster.
I will raise you the opposite point: why deprive people of their ability to have a globally addressable IP address?
>But even UDP should work through CG-NAT.
I have already told you why it is wrong to make such as assumption, haven't I?
I have heard of stories coming from China and Vietnam that some ISPs implement so-called "type 4 NAT", otherwise known as symmetric NAT or NAT with endpoint-dependent mapping.
This kind of NAT is NOT hole-punchable. And because you don't control the NAT, you are simply SOL if one day your NAT decides to switch to it. Can't even use Tailscale without significant service degradation now, ouch.
Granted, I have only heard about it in Vietnam and China, and it's not a national thing -- only some provinces seem to have symmetric NAT implemented. But I feel the need to remind you that the ISPs there were able to get away with it, because the two countries have significant IPv6 presence. [0]
>Port forwarding is nice, but everyone already knows you can hardly run a server at home (even in countries where port forwarding is standard).
You can hardly run a server at home because we have been facing address space depletion since the dot com bubble.
>I hardly understand why it warrants treatment as such a terrible awful disaster.
You haven't faced an overloaded CGNAT gateway, have you? [1]
[0]: https://stats.labs.apnic.net/ipv6/XD
[1]: https://www.reddit.com/r/ipv6/comments/1as8dvy/is_there_a_wa...
