[Bridge] Why should static MAC address match one of the port MAC addresses - bug?
Rolf Fokkens
rolf.fokkens at wanadoo.nl
Sun Dec 19 14:26:22 PST 2010
Hi All,
Despite of what Stephen explains, 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). No arp response or anything else.
So, Michiel's claim seems to be true: the bridge mac address should
apparently be one of the bridge interfaces. But I don't see the logic,
this seems like a bug to me.
kernel is Fedora kernel-2.6.35.9-64.fc14.x86_64.
Cheers,
Rolf
>
> ------------------------------------------------------------------------
>
> * /To/: Michel Lammertink <mlammertink at xxxxxxxxx
> <mailto:mlammertink at DOMAIN.HIDDEN>>
> * /Subject/: Re: Why should static MAC address match one of the
> port MAC addresses.
> * /From/: Stephen Hemminger <shemminger at xxxxxxxxxxxxxxxxxxxx
> <mailto:shemminger at DOMAIN.HIDDEN>>
> * /Date/: Tue, 12 Oct 2010 09:44:08 -0700
> * /Cc/: bridge at xxxxxxxxxxxxxxxxxxxxxxxxxx
> <mailto:bridge at DOMAIN.HIDDEN>
> * /In-reply-to/: <4CB46549.2070901 at xxxxxxxxx
> <mailto:4CB46549.2070901 at DOMAIN.HIDDEN>>
> * /Organization/: Linux Foundation
> * /References/: <4CB46549.2070901 at xxxxxxxxx
> <mailto:4CB46549.2070901 at DOMAIN.HIDDEN>>
>
> ------------------------------------------------------------------------
> On Tue, 12 Oct 2010 15:40:25 +0200 Michel Lammertink<mlammertink at 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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