How to make the transition from a subdomain to an intranet site?

Question

Domain Name System

We have the following task:
the CRM intranet on a local server accessible for example 192.168.1.2/crm
forwarded port 80 on a router with an external 1.2.3.4 hoster to which the domain is delegated has an A
record for office.domen.ru and a static address 1.2.3.4 is entered.
the logic seems to have everything, but the office.domen.ru/crm transition does not work. Tell me in which direction to continue the setup

Answer 1

The web server on the side of your CRM, by any chance, does not write anything about the error in the log? If the network part is done correctly, you have a missing name problem when the client comes in and types in the Host: header.
Logs, in short, look.

Answer 2

What kind of web server do you have on the local server? Maybe in Apache it is necessary to create?

Answer 3

I think I need to dig in the router. Or rather, check port 80, whether it sends to port 80 or to another. There are routers that change ports, since port 80 is usually occupied by the router itself.