I read your tutoral on MAC addresses but I still don't under

I read your tutoral on MAC addresses but I still don't understand why we need a MAC address as well as an IP address. Why is this?

i think it is for security ...MAC address cannot change , but IP can change ...

Hi Mask

I'll try and explain what i have understood, it would be great if Chris acknowledges this explanation.

Here goes...

For 2 computers to communoicate we don't need ip address at all. We can use NetBEUI protocol and they will commmunicate very well. But the problem here is that, NetBEUI is not routable hence not widely used.
IP addresses come into the picture when u use TCP/IP protocol suite.
Now, let us say that TCP/IP wasn't designed with IP address, it will try to use MAC address for communication.
The problem arises, how will u transfer a packet to different networks, in other words how will u route packets to different networks using MAC addresses.
There is no subnet mask or any sort of technique to tell that a particular MAC address belong to a computer that resides in a different n/w.
This is where the beauty of IP address lies, or shud we say beauty of the TCP/IP protocol suite.
We have subnet mask to differentiate between networks, hence packets are routed properly to their destinations.
I hope u understood what i am trying to say.

Bye [img]images/smiles/icon_smile.gif[/img]

Maskkkkkkkkkkkkkkkkkkkkkkk [img]images/smiles/icon_smile.gif[/img],

In every type of network you have two type of addresses, one is a logical (given by software - eg. IP) and the other is a hardware address , which is where the MAC address falls.

If you check the MAC address page, you will see that the logical address exists on layer 3 of the osi model, while MAC addresses are on layer 2.

When a packet arrives at a workstation it will flow up from the physical layer, to the datalink layer (mac addresses) and then to the network layer. The MAC address helps identify the computer to the network as a peice of hardware.

Let me give you a simple example to help you understand why we use MAC addresses.

If you found yourself delivering a letter to a street that had no logical numbering system (e.g the first house on the street was number 80, while the second one was number 23 ...) and the houses had NO numbers outside, what would you need to do ?

You will have to knock on every single house and ask if they are number your looking for e.g 50, and you will do this until you found the correct house.

On the other hand, if each house had its number written outside it, then you will quickly be able to find the correct house and deliver the letter.

Think of the MAC address being the little sign that tells us which number each house is. Once you understand that, then go back and read the MAC section and see how far you can get.

Keep in mind that these concepts can take some time in order to 'sink in'. I remember it took me 6 months to totally understand the OSI model, so don't feel disappointed if you still don't understand it.

If anyone else has some good examples, now would be a good idea to post them!

Cheers,

[ 14 May 2003: Message edited by: Admin ]

the explaination on "houting a house" was interesting examples.Hope to have lot of examples like that..

thank you..

If I may make a recommendation,

There is nothing better than seeing this in action, first read through the material on the site, and familiarise yourself with the protocols and the OSI model, then see how it applies to you -- get yourself a network sniffer -- from here
www.firewall.cx/download-s01-ns.php

Now the output from these tools can be a little daunting at first site as its raw packets you're seeing, but don't worry its actually pretty simple to decode if you have the basics.

Why should you do this ?
To give you an analogy, you may have looked 'under the hood' of your car.. but you'll have an even deeper understanding of how a car works if you're actually inside the engine, watching the pistons go up, watching the fuel mix with air and get ignited by spark plugs etc etc. (dont try this at home kids

Now fire up the sniffer (i recommend IRIS) and do something simple like request a webpage, or ping another computer. Look at all the packets that were sent and recieved... notice the source and destination addresses, the data in the packet (ping will have abcdefghijk or something similar, an webpage request will have the http headers), if you have an understanding of how TCP works, look at the sequence and ack numbers incrementing...

Try to visualise the packet going through your machine.. getting encapsulated with TCP, then IP, then Ethernet (or whatever) and imagine it being converted into 100101010010101... going out onto the wire... passing through a few routers and firewalls... and then being reassembled on the other end.

When you put it under a microscope, networking is jaw dropping.. i mean when you stream a video from across the globe, think of the route that packet goes through... and still comes to you so quickly that you can watch moving video ! I know I'm a networking geek but sometimes I'm just astounded by the way all the sending, routing, filtering etc happens so fast that it is transparent to us !!

Cheers,

btw, if my description a cars internal combustion engine is wrong, forgive me.