Why have a MAC and IP address, why not just use an IP address?"?

Question

I apologize if this question has been previously posted.

Total Newbie Looking For Guidance.

I always read topics that ask, "why have a MAC and IP address, why not just use an IP address?"

Without getting into the technicalities, I would like to give my explanation and have the more experienced members decide if I m correct or not.

A MAC address is a globally unique number and does not get recycled, so that address will remain with a NIC..... 4, 5 or 10 years until EOL.

An IP Address is recyclable and may belong to different hosts over a period of years.

When assigning a truly unique address, one that can stand the test of time, MAC addressing make sense.

Any replies, will be greatly appreciated.

Thank you.

JR

Answer 1

A MAC address is somewhat similar to a person's Social Security Number. My SSN is unique to me, and my laptop's network adaptor has a MAC address that is unique to it.



My current addess in in Easthampton, MA, but if I move to Atlanta, the address used to reach me will change. Likewise, the IP address used to reach my laptop will change to one provided by the new ISP. My SSN doesn't change, and my laptop's MAC doesn't changed. The mailing address and IP address DO change.



Some people do have STATIC IP addresses that do NOT change. I could also have a permanent mailing address in Chicago that would forward my mail to me wherever I was at any moment. My SSN, however, never changes.



The MAC address is used to identify individual network adapters. The IP address tell the internet how to FIND the computer.

Answer 2

A MAC address and IP address are used somewhat differently. The MAC address is used on a local directly connected network. It is not necessarily unique in the world, it just has to be unique on that particular network. But it is not routed, so it could possibly be used in different networks. For example consumer broadband routers usually have the capability to clone a MAC on a computer connected to their LAN to their WAN IP. Or a wireless bridge may be able to clone the Ethernet MAC of a device connected to it as its WiFi MAC. Your PC has no clue of and does not care what MAC addresses are beyond your LAN.



IP address can be routed across different networks, so that is what is used to reach remote machines on the Internet. When an IP is used on a LAN, your PC first does an arp who has request of the IP address and the device with that IP answers "I do" with its MAC address. Then your PC connects to that MAC address. That is stored in your dynamic arp cache.



I little known trick is that if you do not know the IP of a local device, but you know its MAC, you can make a manual static arp entry in your arp cache of its MAC and an IP address, so you can access the device by that IP, even if that device does not have that IP, or any IP, on it. I had to use that to connect to a hand me down print server that our factory thought did not work. The reason it did not work was because someone made a typo setting it to a 192.186.x.x IP instead of 192.168.x.x. So I made a static arp entry assigning its MAC a 192.168.6.x IP for our office network and was able to access it and reconfigure it to a correct IP for our LAN.

Answer 3

Because multiple computers can share a single IP address whereas a MAC address is machine dependent.