Bdtyktl

So, I've been reading around about dynamic DNS and portforwarding, among others here:
Portforwarding to multiple computers

If I gather correctly, this is the scenerio that will unfold in real life: Let's say I want to setup a webserver on my local machine, but I don't want but a dedicated server, so I decide I will use dynamic DNS service with port forwarding, so that each time my current IP allocated by my ISP to me (and to many other users) will direct to my website.

Does that mean that it is impossible for another website of some user that is in the same ISP and is for the current moment behind the same NAT as me, to be reachable at the same time as my website? Because at that situation, we will share the same IP:PORT until one of us will get a new IP from our ISP.

If that's true, that just seems pretty impractical to me. Am I missing something here? Are there no ways to overcome this possible issue?

Hopefully I've made myself clear, as English isn't my native language.

Yes, technically you would be correct – but in practice, if you're behind ISP-controlled NAT, then you generally cannot set up port forwarding in the first place.

When you're behind a CGNAT and share the address with other customers, it doesn't matter if you configure some port-forwarding rules on your own router; they will have no effect on the ISP's routers which actually 'own' the public address – only the ISP can provide port-forwarding. And in most cases, the ISP will refuse to do it.

So yes, it's impractical, and that's why in practice it isn't done in the first place.

When people actually use port forwarding, it's used with ISPs which don't implement CGNAT yet – they assign a public IP address directly to a single customer. Yes, the IP:port can still be forwarded to one device only, no matter where NAT happens... but the problem isn't nearly as significant because there's no sharing between customers – only between devices belonging to the same LAN.

(In the case of HTTP, it's even less significant because the customer can set up a reverse proxy and route HTTP requests to different devices based on the domain name.)

Finally, note that Dynamic DNS is completely unrelated to this. All it does here – well, all that regular DNS does – is assign a name to the IP address, but the actual traffic doesn't know the difference. When a browser tries to set up a connection to your webserver, the IP and TCP packets look exactly the same whether DNS was used or not.