Every single router I ever had, including ISP provided ones had the option to port forward.

Not MiFi or other cellular connections, unless you get a special type of service. Might not be NAT, but it's definitely firewalled upstream against opening ports for listening.

> One problem is that many ISP's use NAT, meaning that other computers can't connect to your computer! Unless your computer initiated the connection. Most ISP's will give you a public IP if you ask though.

Actually, my experience has been the exact opposite on both points with every ISP I've ever had (in the United States). I've never had a problem setting up a dynamic DNS server to access my home network from outside. Likewise, I've never had an ISP that will give you a static IPv4 address. Maybe it's just luck on my part, but I was under the impression mine was the most common experience these days (for this country).

Carrier grade NAT might be a problem. In some networks, IPv4 traffic goes over a non-unique public IP address assigned to multiple users.

I live in Canada. I have a public version 4 IP address, although it is dynamic, but does not change that often. However, they once changed it to use NAT, but I was able to disable NAT easily enough on the modem, so that I could use a proper internet connection.

In most places, you need a "business" connection to get static IPs. I have several at home.

Assuming that an IP address is only assigned to you and not to other users (via a NAT that you have no control over), it's easy to occasionally ping your DNS server with your IPv4 address and assign a hostname to it.

If your DNS provider has an API, it's probably the first example in the API documentation. If not, there's DuckDNS and similar.

This is true, though there are still often port limitations. For example, with residential connections here, port 25, 80, and 443 are filtered incoming, so you can't run a web server or SMTP server on a normal port. Also servers technically violate the AUP. Business connections have no such restrictions.

Isn't NAT managed by your router? Or do you mean the "public ip" for your home is actually a local ip inside your ISP's network?

Static IP isn't necessary for hosting from home but a "Non-NAT" connection is. If you don't have a static IP, you can use a service such as dynaDNS or something which runs on your server and keeps informing your subdomain to use the ever changing dynamic address. But if your device sits behind a NAT, then its not accessible from outside at all (unless the device initiates the connection), thus its impossible to host if your ISP has placed you behind a NAT. But the plus point, on the other hand, is increased security which is probably good for the majority of people.

Or you use Amazon|DigitalOcean|anyproviderwithanapi with low TTL and set up your own dynamic DNS.

One problem for ISP is that there are not enough IP addresses. local IP's have been used for mobile connections for a while, and now also for stationary connections.