As the port numbers are standard on a firewall, why dont the administrators just use random numbers? Would these be the same for a proxy firewall? How would a NAC work with a firewall?

Firewall port numbers - Clearly summarize the function of the port numbers on a firewall and on a proxy firewall.

NAC and firewall- Accurately and thoroughly explain how an NAC works with a firewall.

This subject matter is for my CyberSecurity course:Securing the Network, Firewall Design, Technologies Involved with Firewalls, and Perimeter Security Maintenance