You've supposed to call IEEE and buy another block once you hit 0xFFFFFF in
the lower 6 hex digits. Sometimes I've recovered some numbers from boards
that have been returned, scrapped, and replaced, but that's a bookkeeping
hassle. I haven't manufactured network adapters for about 4 years now so
things might have changed. I suggest you check with IEEE for up to date
info. IEEE refers to the 6 hex digit number as an "Organizationally Unique
Identifier" or OUI. See http://standards.ieee.org/regauth/oui/index.shtml
to see current assignments or apply for a block. They ain't free, though.
One thing you can do in situations where you or your customer have complete
control over all adapters on the LAN is to allow redundant assignment of
numbers. I've supported this for example in sales of adapters to OEMs of
bank security systems. As long as the OEM never connected together two nets
from different banks, they were able to recycle the same sequence. Of
course with all the acquisitions that have gone on in recent years, this is
not a totally safe assumption.
-- Tom Taylor
----- Original Message -----
From: "Ken Patel" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, September 21, 2000 4:54 PM
Subject: Re: [TN] Need basic info on MAC address
> So, after getting first number, can we create our own as far as they are
not
> duplicated in sequential fashion? I was of the impression that IEEE issues
> the block of numbers and once we used them all, call IEEE and get another
> block.
>
> Please clarify.
>
> re,
> ken patel
>
> -----Original Message-----
> From: McMonagle, Mike [mailto:[log in to unmask]]
> Sent: Thursday, September 21, 2000 10:32 AM
> To: [log in to unmask]
> Subject: Re: [TN] Need basic info on MAC address
>
>
> Tom,
> I appreciate for the clarification, I didn't know
> that the IEEE controlled MAC addresses. I had though that they were
> user-developed, as long as they were not duplicated within their own
> products. Learn something new everyday, thanks....
>
> Mike
>
> -----Original Message-----
> From: William T. (Tom) Taylor
> [mailto:[log in to unmask]]
> Sent: Thursday, September 21, 2000 12:20
> PM
> To: [log in to unmask]
> Subject: Re: [TN] Need basic info
on
> MAC address
>
> 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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