Short answer
What is an interface address?
Network interfaces have two addresses:
A layer 2 address - The MAC address (Also called Hardware , physical or burned-in address).
A layer 3 address - The IP address (version 4 or 6).
What is it used for?
Both addresses are used in order to communicate between network devices.
MAC address - to uniquely identify every node (e.g., workstations and printers) on a network.
IP Address - used in order to communicate with a device on a network, or between different networks.
*How is it different from a normal IP address in a network?*
By ‘normal’ IP address you probably mean the gateway (router) external IP - this is what you will see if you’ll search “what is my IP address” in Google.
If you didn’t mean the router - so the normal IP addresses are probably the network interface IPs.
Some more information:
A MAC address is a six-byte identifying number which is permanently embedded in the firmware of the adapter. It is readable by the network and the OS of the device on which the adapter is installed. Every adapter has a unique MAC address.
Because MAC addresses never change, they are very useful on preventing unwanted network access by hackers and intruders. Read more about MAC filtering.
The IP address of network interface is in most cases a dynamic, private IP address which was given to the network interface by the DHCP (server or router).
If device A and device B are on the same network, and the MAC address of device B is known by device A - they can communicate directly based on the MAC addresscommunicate directly based on the MAC address.
If the two devices are on different networks, they will have to go through a router and the communication is done one level up in the TCP/IP model and will be based on the IP addresses.
The mapping between the IP and MAC address is done by the ARP protocol.
