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

              The NOSPIN Group is now offering Free PC Tech
                     support at our newest website:
                          http://freepctech.com