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

/  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)./

/ 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]?/

/ [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./

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

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* /To/: Michel Lammertink <mlammertink@xxxxxxxxx <mailto:[email protected]>>
* /Subject/: Re: Why should static MAC address match one of the port MAC addresses.
* /From/: Stephen Hemminger <shemminger@xxxxxxxxxxxxxxxxxxxx <mailto:[email protected]>>
* /Date/: Tue, 12 Oct 2010 09:44:08 -0700
* /Cc/: bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx <mailto:[email protected]>
* /In-reply-to/: <4CB46549.2070901@xxxxxxxxx <mailto:[email protected]>>
* /Organization/: Linux Foundation
* /References/: <4CB46549.2070901@xxxxxxxxx <mailto:[email protected]>>

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Quoted 10 lines · On Tue, 12 Oct 2010 15:40:25 +0200 Michel Lammertink<mlammertink@xxxxxxxxx>…

/  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.

Quoted 3 lines

/ 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.

Quoted 8 lines

/ [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./