MAC/IP Question

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Hey guys,

Currently working through my Cisco book, and I've come across Ethernet addressing, MAC addressing for your NIC etc, I just wondered, why would you need both a MAC address and an I.P address, don't they both serve the same purpose?

Sorry if thats a totally stupid question guys, just wrapping my head around it thats all! thanks a bunch!

 

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MAC address are used to communicate with networking devices at layer 2. MAC address are also permanent and are tied to your network interface card. IP addresses are used for communication at layer 3 and are not permanent, meaning IP address can be reassigned to other networking devices as long as no other device on the same network has the same IP. If you're reading the cisco book, you probably came across how switches and routers communicate, you've also probably saw that switches and routers communicate at different layers of the OSI model, hence the need for MAC and IP addresses.

 

MAC is a hardware address of a device. Generally speaking can be said to be totally unique in the world, although realistically not always the case as you can change a MAC address ;) You can get information such as manufacturer from a MAC address.

IP is a network address assigned to something on a network, obviously this can be changed depending on what you need to do with the device.

So say think of it like a car, the MAC address is the VIN number/serial number of the car, it'll never change, it uniquely identifies the vehicle. The registration plate is an identifier on the car at that point in time, but can be changed to suit if needed.

So if you moved the car to another country (a bit like another network), you change the reg plate so it fits in, but still retains it's original VIN/serial etc.

So they service similar purposes, however whilst an IP address is assigned depending on the network the machine is on, it will always retain it's unique hardware address.

And as said above in networking terms they used at different levels for different things. Very generally speaking switches talk in MAC, routers talk in IP

 

yep as you continue through your book it wil become more clear, however one thing to note:

When two devices are communicating using IP (discounting more advanced topics like NAT etc), the source and destination IP address stays the same as the packet hops from network to networks. However, the source and destination MAC address is constantly changing as it hops from client to router to router to server.

 

I think reading up on ARP will also help you understand what is happening...

 

Also, IP gives us the ability to summarize IP networks in our routing tables, and spread IP subnets geographically.