[Xen-devel] Fwd: ARP problems in -testing?

[Tim Durack <tdurack@xxxxxxxxx>]

There are four types of MAC addresses:

Globally Unique
*0-**-**-**-**-**
*4-**-**-**-**-**
*8-**-**-**-**-**
*C-**-**-**-**-**

Locally Administered
*2-**-**-**-**-**
*6-**-**-**-**-**
*A-**-**-**-**-**
*E-**-**-**-**-**

Multicast
*1-**-**-**-**-**
*3-**-**-**-**-**
*5-**-**-**-**-**
*7-**-**-**-**-**
*9-**-**-**-**-**
*B-**-**-**-**-**
*D-**-**-**-**-**
*F-**-**-**-**-**

Broadcast
FF-FF-FF-FF-FF-FF (Could be considered an all-stations multicast)

Locally administered addresses can be considered private ethernet:

(LAA) are MAC addresses which have the second least significant bit
(LSB) of the first octect is set to '1' (for example, 'xxxxxx1x'. LAA
enable administrators to assign MAC addresses using their own scheme.
When an LAA is assigned, it overrides the in-memory copy of the Global
address during driver initialization. So the burned-in address on the
Ethernet adapter is never actually changed, only the in-memory copy.
LAA create the possibility of assigning duplicate MAC addresses, which
makes for some very interesting network problems. Fortunately, they
are rarely used in Ethernet environments, but are fairly popular in
Token Ring networks.

The Xen addresses are in the LAA range, so scheme wise you are safe to
do whatever you want with them.

Alternatively XenSource could spring for an OUI or IAB, not really
that expensive:

    The OUI is $1,650.00 (US); the IAB is $550.00 (US)

IAB = Individual Address Block, 12 bits of address space instead of 24.

Tim:>


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