Re: Why should static MAC address match one of the port MAC addresses.

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Hi all,

I'm having the problem Michiel describes as well. I have a bridge br2 containing 1 (but potentially more) tap interface for kvm. Windows 7 VM doesn't like the bridge mac address to change, so I try to make it fixed.

ifconfig br2 hw ether 02:00:00:00:01:02

Interface br2 becomes instantly unreachable from the VM (via the tap interface).

So, Michiel's claim still seems to be true: the bridge mac address should apparently be one of the bridge interfaces.

I don't see the logic, this seems like a bug to me.

Cheers,

Rolf



On Tue, 12 Oct 2010 15:40:25 +0200 Michel Lammertink <mlammertink@xxxxxxxxx> wrote:

> Hi all,
> 
> I've read many messages on this mailing list with the question about
> setting a static MAC address on the bridge interface, but two questions
> remain:
> 
>  1. Why should the MAC address of the bridge match the address of one of
> its interfaces? Setting the MAC address to a different value does not
> generate an error, but the bridge is not working properly (Local data
> does not arrive).

No longer a requirement. It was just a good way to ensure a good
address that was unique, and not being used by other systems.

>  2. Why does the bridge by default choose the "lowest" MAC address,
> instead of the MAC address of the first port added, as is proposed by
> the standard [1]?

It was a convenience in original design to choose a consistent value.
Since ports can be added in any order, using the lowest seemed like
a good idea for the original author. This has been maintained for
backwards compatibility.

> [1] IEEE802.1D, Par. 7.12.5.
>     Quote: "The Bridge Address may be the individual MAC Address of a
> Bridge Port, in which case, use of the address of the lowest numbered
> Bridge Port (Port 1) is recommended."
> 
> Thanks in advance,
> 
> Michel.
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