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Date:      Sun, 26 Aug 2001 16:43:56 -0700
From:      "Kevin Oberman" <oberman@es.net>
To:        Brian Reichert <reichert@numachi.com>
Cc:        Harry Putnam <reader@newsguy.com>, freebsd-mobile@FreeBSD.ORG
Subject:   Re: Frustrating network problem - need diagnotic help 
Message-ID:  <200108262343.f7QNhuR11424@ptavv.es.net>
In-Reply-To: Your message of "Sun, 26 Aug 2001 13:03:47 EDT." <20010826130347.A81961@numachi.com> 

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> Date: Sun, 26 Aug 2001 13:03:47 -0400
> From: Brian Reichert <reichert@numachi.com>
> Sender: owner-freebsd-mobile@FreeBSD.ORG
> 
> On Sun, Aug 26, 2001 at 06:55:38AM -0700, Harry Putnam wrote:
> > How does one tell if it is a bogus MAC address?
> 
> I initially had to cheat, and look at how Windows probed that card,
> for in that OS, it worked.  Ultimately, I researched the fields of
> the MAC address and found that:
> 
> - From your supplied URL, the vendor is [Toshiba America]
>   [3COM/NoteWorthy 56K Modem]
> 
>   Comparing the first three bytes or your MAC 01:d4:ff:03:00:20 against any
>   MAC vendor list implies a mismatch:
> 
>     <http://map-ne.com/Ethernet/vendor.html>;
>     <http://standards.ieee.org/regauth/ethertype/type-pub.html>;
> 
> - Although, for the life of me I can't reaconstruct the research,
>   I recall learning that that list bit of the MAC address must be
>   '1', otherwise, it's interpreted as a multicast address.  (Which
>   only makes sense in a destination address, not a source address,
>   which it what your card's MAC will be used for.)
> 
> > What do you mean by
> > `certain' above?  There were some tcp connections you could not make?
> 
> I whined to -mobile and -isp, with some feedback.  Look for these
> subjects:
> 
>   'linksys vs cisco'
>   'LinkSys NP100 vs the universe'
> 
> No solutions are discussed, but I go into great detail of the
> sypmtoms I was seeing in different environments.
> 
> In my case, though, it came down to a buggy ed driver in FreeBSD
> 4.0-RELEASE, when 4.1 came out I uprgaded, and voila! I had a
> working NIC.

For all of you who don't have a copy of 802.3 handy, there are two
special bits in a MAC address. They are the first two bits on the wire
in the MAC, but because of the bit ordering on the wire, these are the
last bits of the first byte of the MAC.

The first bit is the "group address" bit. This means multicast or
broadcast. (Broadcast is simply a special case of multicast.) It
should NEVER be set in the source address, so the first octet must be
even. 

The second bit the "locally administered" bit, indicating that the MAC
address is locally assigned and not always globally unique. Some
protocols like DECnet IV and Xerox PUP make use of this, but it is
pretty much unused these days.

In any case, a MAC address with an odd first byte is clearly not legal
as a source address.

R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman@es.net			Phone: +1 510 486-8634



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