How to understand what is wrong with the network?

Question

Computer networks

1000 and 1 time I set up something like this, but something is happening here that is not clear to me.
In general, I don’t do anything complicated - I need the port to be accessible from the outside.
For the test, I wanted to forward the 80th port to the web server of a specific computer on the local network.
Available:

• Router with no-ip and configured forwarding (port 80 at 192.168.1.134).
  
• A configured and running web server listening on this port.
  
• The problem is that neither the domain nor the external IP is pinged, and the domain does not connect from networks other than the local one
  

What’s odd is that the external ip that the router writes is 100.64.54.* (and this IP is also written in the provider’s personal account), and all sorts of services (like 2ip.ru) write 194.58.181.*.
Moreover, if you connect the Internet directly to the computer (bypassing the router), then IP 42.56.33.* is issued and everything works fine.
Moreover, for the same provider in another apartment, a similar scheme works fine.
I sin on the router (mercusys ac12), but there I already checked all the checkboxes, but to no avail

Answer 1

In general - as it turned out, the provider was cunning here. Apparently, as soon as he starts to run out of white IPs, he starts giving out gray ones, just before that I was lucky.
Thanks to all.

Answer 2

external ip, which is written by the router 100.64.54.* (and this IP is also written in the provider's personal account), and all sorts of services (like 2ip.ru) write 194.58.181.*.
Moreover, if you connect the Internet directly to the computer (bypassing the router), then IP 42.56.33.* is issued and everything works fine.

100.64.0.0 - 100.127.255.255 (subnet mask 255.192.0.0 or /10) - This subnet is recommended by RFC 6598 for use as addresses for CGN (Carrier-Grade NAT). ( pedivicia )

The address of your router is gray, that's all

Answer 3

Problems like this, especially with networks, are solved by elimination , where you make a big guess, test it with an experiment, and then cut off half the possible causes of the problem. For example, "there is a ping, it's definitely not a problem with the wires", etc.
But here one must be careful in judgments and conclusions. Insidious causes are all sorts of intricate schemes that work under specific conditions that are difficult to guess. For example, saying "this is definitely not a provider" can be mistaken if the provider changes its behavior to a completely different one depending on the conditions (poppy address, TTL, time of day, etc.). Just in case, it is advisable to do small checks to exclude these options, although they are unlikely.
To exclude the router (its software), the easiest way is to try a completely different router, and find the same problem there. If there is no problem with another router, then this does not mean that the problem is in the previous router. But if there is a problem again, then the problem is definitely not in the previous router: it cannot be in two different routers at once. You just remove the router from the chain, this is not the same, because you touch on many more possible causes, and therefore much more careful conclusions are needed.
PS In general, it usually turns out to be "mixed up the numbers" or "forgot an elementary thing", etc. Luck with searching!