MAC address confusion

Mailman List Mirror (Read Only)
1

Whic one of these, is locally assigned unicast MAC address, when talking about
output format CSCO uses?

4000.0000.0000 (Local IXPs choice)
0200.0000.0000 (My money is here)

http://standards.ieee.org/regauth/oui/oui.txt
02-07-01 (hex) RACAL-DATACOM
A0-6A-00 (hex) Verilink Corporation

In either case two of the lowest or highest bits of 1st octet seems to be
happily used to assign addresses. What am I missing here?

2

Whic one of these, is locally assigned unicast MAC address, when talking about
output format CSCO uses?

4000.0000.0000 (Local IXPs choice)
0200.0000.0000 (My money is here)

the second one. most significant byte is on the left, but within the
byte, most significant bits are on the right. so U/L bit is the second
one counting from the left.

http://standards.ieee.org/regauth/oui/oui.txt
02-07-01 (hex) RACAL-DATACOM

good point, dunno.

3

http://standards.ieee.org/regauth/oui/oui.txt
02-07-01 (hex) RACAL-DATACOM
A0-6A-00 (hex) Verilink Corporation

In either case two of the lowest or highest bits of 1st octet seems to be
happily used to assign addresses. What am I missing here?

After enabling DECnet routing, the interface MAC address turns to
something like this:

GigabitEthernet0/2 is up, line protocol is up
  Hardware is BCM1250 Internal MAC, address is aa00.0400.0a04 (bia 000b.bffd.fc1a)

And you'll find

AA-00-04 (hex) DIGITAL EQUIPMENT CORPORATION

in the list. I don't know what 02-07-01 is, but I guess that could be
something similar: The OUI belongs to a company, but they don't use the
addresses to burn them into interface cards.

Andras

4

Hey,

> http://standards.ieee.org/regauth/oui/oui.txt
> 02-07-01 (hex) RACAL-DATACOM

After enabling DECnet routing, the interface MAC address turns to
something like this:
  Hardware is BCM1250 Internal MAC, address is aa00.0400.0a04 (bia 000b.bffd.fc1a)
AA-00-04 (hex) DIGITAL EQUIPMENT CORPORATION

in the list. I don't know what 02-07-01 is, but I guess that could be
something similar: The OUI belongs to a company, but they don't use the
addresses to burn them into interface cards.

I guess you shouldn't be able to assign 02 (or AA) to a company for ethernet
number, much in the same way you shouldn't be able to assign RFC1918.
However you are right, it seems that these are unexplained exceptions to rules:

http://www.iana.org/assignments/ethernet-numbers
'some of the known addresses do not follow the scheme (e.g., AA0003; 02xxxx)'

Would be interesting to see what are the historical reasons.Perhaps they simply
predate the scheme or some might not even co-exist in ethernet network to begin
with, in which case they might be better documented elsewhere.
  In any case, to avoid collision with history, better start with 06 which
seems cruft free, instead of 02, when choosing local MAC address prefix.

As a side note, the 40 prefix used as local MAC in IXP here, seems to be
just mistake in assuming ethernet follows tokenring in numbering scheme.