What's the difference between a Mac Address and an IP Address?

MAC and IP addresses are both key components to network, but they serve different purposes, and are visible in very different ways.

A MAC (or Machine Access Control) address is best thought of as a unique serial number assigned to every network interface on every device. And by unique, I do mean unique; no two network cards anywhere should have the same MAC address.

MAC addresses are 6-byte (48-bits) in length, and are written in MM:MM:MM:SS:SS:SS format. The first 3-bytes are ID number of the manufacturer, which is assigned by an Internet standards body. The second 3-bytes are serial number assigned by the manufacturer.

Operating Systems support various command-line and GUI utilities to allow users to find MAC address of the system. On Unix variants including Solaris and Linux support "ifconfig -a", "ip link list" or "ip address show" command that displays MAC address of the network device among other useful information. You can see your network interfaces MAC addresses using the command prompt in Windows including NT, 2000, XP and 2003 support "ipconfig /all" command that displays MAC address. On a MacOS, one can find MAC address by opening "System Preferences", then selecting "Network".

For example the result using command prompt in windows:
Ethernet adapter Local Area Connection 2:
.
.
Physical Address. . . . . . . . . : 00-22-FA-5A-B4-C2

An IP address is assigned to every device on a network so that device can be located on the network. The internet is just a network after all, and every device connected to it has an IP address so that it can be located. For example, The IP address is at 172.16.254.1. That number is used by the network routing equipment so that when you ask for a page from the site, that request is routed to the right server.

The computers or equipment you have connected to the internet are also assigned IP addresses. If you're directly connected, your computer will have an IP address that can be reached from anywhere on the internet. If you're behind a router, that router will have that internet-visible IP address, but it will then set up a private network that your computer is connected to, assigning IP addresses out of a private range that is not directly visible on the internet. All internet traffic must go through the router, and will appear on the internet to have come from that router.

The following is an illustration or metaphors of between IP and MAC address:

An IP Address is kind of like your postal address. Anyone who knows your postal address can send you a letter. That letter may travel a simple or complex route to get to you, but you don't care as long as it makes it.

The same is true of packets of data traveling on a network like the internet. The IP address indicates where a packet is destined, and the system takes care of getting it there. A letter may or may not also have a return address so you know who to write back to - a TCP/IP address always has a return IP address.

A MAC Address is kind of like the color, size and shape of your physical mail box. It's enough that the postal carrier (your network router) can identify it, but it's unique to you, there's no reason that anyone other than your postal carrier might care what it is, and you can change it by getting a new mailbox (network card) at any time and slapping your name (IP address) on it without affecting your delivery.

As Summary the difference between MAC and IP Address:
1. MAC address is supposedly unique to each network interface card while an IP address is usually replaced
2. An IP address reveals which element on which network it is while the same cannot be extracted from a MAC address
3. MAC is one of the security methods in WiFi
4. Both IP and MAC addresses can still be spoofed or copied

source: ask-leo by Notenboom