With a few exceptions, every Ethernet adapter in the world has a unique
48-bit MAC address, or 12 hex digits.  A vendor reserves a block of
addresses from the IEEE, and is assigned one or more unique 6 hex digit
values that will form the most significant portion of the MAC address.  The
vendor then sequentially assigns numbers from this block to individual
adapters by incrementing the least significant 6 hex digits.  This value is
typically stored in onboard FLASH so it is possible to change it for special
circumstances.  Network analyzers can usually identify the manufacturer of
the adapter that sent a packet by looking up the first 6 hex digits of the
MAC address in a table.  Many schemes rely upon the uniqueness of the MAC
address.  It can be used to assign a Globally Unique Identifier (GUID) to
module interfaces developed on that computer.  It may be embedded in
software that doesn't use a dongle to restrict the use of that software to a
single machine.  It may be put on a reservation list in a DHCP server so
that the same IP address is always assigned to the machine containing that
adapter.  It is also very important in the low levels of TCP/IP for directly
routing a packet to a specific host.

-- Tom Taylor

----- Original Message -----
From: "McMonagle, Mike" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, September 21, 2000 12:41 PM
Subject: Re: [TN] Need basic info on MAC address


>                 Ken,
>                         MAC addresses are used to unique addresses that
> identify duplicate devices on a network that are from the same
manufacturer,
> such as network cards. There is no controlling organization, you create
them
> yourself for your specific products, and you control them to prevent
> duplication of the same address being used on multiple units. You can get
a
> short primer on the various network addressing schemes at :
>
>
http://www.ieng.com/univercd/cc/td/doc/cisintwk/ito_doc/introint.htm#xtocid1
> 304523
>
<http://www.ieng.com/univercd/cc/td/doc/cisintwk/ito_doc/introint.htm#xtocid
> 1304523>
>
>                 Mike McMonagle
>                 Senior SMT Engineer
>                 Telxon Corporation
>                 www.telxon.com <http://www.telxon.com>
>
>
>                                 -----Original Message-----
>                                 From:   Ken Patel
> [mailto:[log in to unmask]]
>                                 Sent:   Thursday, September 21, 2000 10:57
> AM
>                                 To:     [log in to unmask]
>                                 Subject:        [TN] Need basic info on
MAC
> address
>
>                                 What is MAC address and how is being
> controlled? Who issue them? Are there
>                                 many ways to control it?
>
>                                 re,
>                                 ken patel
>
>
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