How to use a MAC Address for LAN IP address Reservation
Channel: W6FCC Videos
Date: 27/11/2019

The MAC Address (Media Access Control) is a Hardware unique Identification that can be used by your DHCP Server (Dynamic Host Configuration Protocol)  function to always assign the SAME IP address to a known MAC address that may appear (and disappear) from your network (Powered on, Powered off).

For PORT Forwarding access from outside your LAN (Local Area Network) you will connect to your public IP address (assigned by your Internet Service Provider -- ISP) using a PORT number that the Router uses to know what INTERNAL LAN address it should forward those packets. This is also known as "Port Forwarding" (Network Address Translation from an outside Network IP to your Inside LAN IP). Some routers ALSO support "Port Translation" as well, so you could come in on, say port 2221 to an internal device on your LAN, and the router will forward to the appropriate LAN Address AND change the port from 2221 to port 21, used as the standard TCP Port.

Using DHCP is great, especially for devices that appear and disappear a lot, like an iPhone, iPad, TV, Android device, or visitor who you allow to use your WiFi to access the internet.

BUT for devices you plan to access remotely, using Port Forwarding, network address translation (NAT) you do NOT want a randomly assigned LAN address for that device because if the address changes, your router will NOT forward packets to the appropriate device, and you will NOT be able to access a device when the internal LAN Address changes and you have not updated the Port Forwarding. 

A new IP address will be assigned at different times. If you reset your Router, upgrade it, or turn off the device you want to access, turn on a DIFFERENT device and the DHCP server gives that NEW device the address of your original hardware (like a radio on the LAN port).

Use DHCP for most devices, but understand WHY you might want to assign a FIXED IP to some devices, and setup your DHCP server to AVOID a block of LAN Addresses that you will be using for devices with a FIXED IP.

Maybe this video will help.

Jeff Towle, Ph.D.  W6FCC  November 27, 2019