From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4D0E868E.4010309@wanadoo.nl> Date: Sun, 19 Dec 2010 23:26:22 +0100 From: Rolf Fokkens MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------080308020508000202030309" Subject: Re: [Bridge] Why should static MAC address match one of the port MAC addresses - bug? List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: bridge@lists.linux-foundation.org This is a multi-part message in MIME format. --------------080308020508000202030309 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 > > * /Subject/: Re: Why should static MAC address match one of the > port MAC addresses. > * /From/: Stephen Hemminger > > * /Date/: Tue, 12 Oct 2010 09:44:08 -0700 > * /Cc/: bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx > > * /In-reply-to/: <4CB46549.2070901@xxxxxxxxx > > > * /Organization/: Linux Foundation > * /References/: <4CB46549.2070901@xxxxxxxxx > > > > ------------------------------------------------------------------------ > On Tue, 12 Oct 2010 15:40:25 +0200 Michel Lammertink 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./ --------------080308020508000202030309 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit 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

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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