>>??Why MAC and IP??<<

[Invisible§niper]

Hi again,

I have been learning about networks in detail lately. And I came across something that I couldn't understand, it has to do with ARP(Address Resolution Protocol), MAC, and IP addresses.

Alright here is what I couldn't understand, for example... while using a router based network a computer on a network needs to send data to another computer/device on the network, what it does is basically shouts out for the computer with a specific IP address. For example it might shout out, "I need to know where 192.168.1.24 is" and it will shout this out to all the computers/devices on the network. Then once the computer with that IP address hears this it will send a message to the querying computer stating that it is the computer that matched the query and then it will also send in that message its MAC address so that the querying computer can add it to its ARP table or MAC address table.

Ok simple enough... but what I do not understand is that the querying computer already had the IP address, which identified the needed computer. Why does it also need that MAC address, why doesn't it only have an IP table, since the IP address was the key that located the computer it needed. Why can't or why don't the hardware vendors just let computers/devices communicate with each other IP addresses and not use MAC addresses?

[homecomputeraid]

For LAN communication (communication within the same subnet), the conversation occurs between end devices using MAC addresses, thus the whole ARP thing. To check your ARP table on a Windows based machine, type arp -a at the command prompt.

For devices which are not on the same subnet, the router on the 'foreign' subnet (the end subnet where the device you're trying to talk to) does the ARP request and gets the packet to its final destination.

Are you familiar with the ISO's OSI Model? IP Addressing is Layer 3. Once the packet is on the correct subnet, then Layer 2 communication has to occur.

Very cool that you're learning some of what goes on behind the scenes. :)

[Invisible§niper]

For LAN communication (communication within the same subnet), the conversation occurs between end devices using MAC addresses, thus the whole ARP thing. To check your ARP table on a Windows based machine, type arp -a at the command prompt.

For devices which are not on the same subnet, the router on the 'foreign' subnet (the end subnet where the device you're trying to talk to) does the ARP request and gets the packet to its final destination.

Are you familiar with the ISO's OSI Model? IP Addressing is Layer 3. Once the packet is on the correct subnet, then Layer 2 communication has to occur.

Very cool that you're learning some of what goes on behind the scenes. :)

What I was thinking is that because, for example hard drives do not know what the IP protocol is and can not speak in that language at all, nor do they know what an IP address is... hardware needs MAC addresses to identify themselves within the computer system thus all pieces of hardware have MAC address for reference. Also hence the name Media Access Control, that being that the system, as a whole has control over the access of the different devices and they can refer to them by their MAC addresses. And well if a network card did not have a MAC address it could not be refered to by any other device it would be nameless!

Does this make sense to you? I mean I might not be right, but does it make sense?

<b>::EDIT::</b>I thought I might also add this link, it's a realy interesting pixar video called "Warriors Of The Net" and it's about what happens behind the scenes of TCP/IP connections. I really liked it and I'm sure you will too, especially if you're a networking fanatic :)

[homecomputeraid]

I understand it, but it's not correct.

I'm not sure whether you're talking about Hard Drive (storgage device), or referring to the Central Processing Unit (CPU) when you refer to Hard Drive, but in either case, the purpose of the OSI Model is to make it so the application involved doesn't have to directly know anything about the intricacies of how the communication is occuring between computers.

The OSI reference model's purpose is to allow networking protocol's at different layers to operate with the same layer at the other side without knowing what's going on in layers above or below it. For example, the browser on your side resides at (or in some cases above) the Application layer. It communicates with the Application layer on the web server side without knowing anything about what happens from layers one through six.

[Invisible§niper]

I understand it, but it's not correct.

I'm not sure whether you're talking about Hard Drive (storgage device), or referring to the Central Processing Unit (CPU) when you refer to Hard Drive, but in either case, the purpose of the OSI Model is to make it so the application involved doesn't have to directly know anything about the intricacies of how the communication is occuring between computers.

The OSI reference model's purpose is to allow networking protocol's at different layers to operate with the same layer at the other side without knowing what's going on in layers above or below it. For example, the browser on your side resides at (or in some cases above) the Application layer. It communicates with the Application layer on the web server side without knowing anything about what happens from layers one through six.

I forgot to add the link to that video, anyway here it is it's worth watching, I'm sure you'll like it:

ftp://www.jcu.edu.au/pub/Videos/Warriors%...0the%20Net.mpeg

[Invisible§niper]

Sorry for double posting but I have found out why network devices have a MAC and an IP now. It's basically because when data is transferred over a distance from router to router to router ect. You always need a source address and a destination address(MAC) and the destination address will change for each hop, and so will the source address. This part is basically if one router realises that there is damage data frames, it will request re-sending of those frames from the previous address.

But these data frames still need two bits of important information, which are the originating IP address (source address that doesn't change) and the destination IP address (the place where the data needs to finally reach).

So to sumerise, the MAC address; source and destination changes along the data-frame's journey. But the final destination and the very original souce address doesn't change (IP addresses).

[homecomputeraid]

Sounds like you have it now.