So long as you get the idea, I guess. The seven-layer OSI model is not very 
easy to analogize for the non-geek, and even for the geek, it can be a pain. 
Thanks for your help. :)

----- Original Message ----- 
From: "David Gillett" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, April 24, 2008 8:06 AM
Subject: Re: [PCBUILD] MAC address corrupted?


> On 22 Apr 2008 at 10:18, Kenneth Whyman wrote:
>
>> Allow me to explain a little better. MAC stands for Media Access Control,
>> and it is a common way of giving network devices a hardware address. Each
>> device has one, sorta like latitude and longitude coordinates on a map. 
>> Each
>> device gets one that is unique and unchanging, and only the next device 
>> or
>> devices that see your device will ever know about it. To talk further 
>> down
>> the chain, you need an address that can be passed along, and that is what 
>> IP
>> is. It's like sticking house numbers onto those map coordinates. They 
>> both
>> mean the same thing, just that one is easier to pass around. MAC is only
>> good for talking between points A and B which are directly connected to 
>> each
>> other on a cable or a wireless link. IP allows you to stretch your
>> communications from point A to point Z way on the other side of the net.
>> Another way to look at is is using a bucket brigade. MAC gets the bucket
>> (your data) between individual people (network devices) in the chain, and 
>> IP
>> makes sure the bucket goes all the way down the chain end to end.
>
>  There are a couple of problems with this analogy.
>
>  One is that a MAC address is completely *unlike* latitude and longitude 
> in
> that it has no association with location at all.  If two devices have MAC
> addresses that are "close" to each other, it probably means they once came
> off the same assembly line around the same time, not that they are in any
> sense close to each other NOW.  IP addresses are much more like latitude 
> and
> longitude, in that they are likely to change if a device is moved to a
> different place in the Internet -- and traffic routing can generally be
> based on that info.  (For *public* IP addresses, anyway...)  IF a remote
> site obtained your MAC address, it might imply what kind of NIC you were
> using, but not where or how to reach it.
>
>  The other big problem is the notion of "next device", which really needs
> to specify "next LAYER 3 device".  The MAC address will propagate through
> any number of layer 2 devices (hubs, switches, wireless access points), 
> but
> not through a layer 3 device (routers, or most separate hardware 
> firewalls).
> Don't worry if you don't have a router -- your ISP probably has several
> between you and the rest of the Internet.
>
>  Here's a better analogy:  When I show up at your door in a taxi, there's
> nothing about it that tells anyone what flight I came into town on or what
> taxi took me from my home to the airport from which that flight took off.
> Each of those identifiers was only meaningful for one leg of my journey -- 
> and that first cab driver didn't need to know what city I was going to
> visit, just that I needed to get to the airport.
>
> David Gillett
>
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