From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Tue, 11 Mar 2008 08:23:47 -0700
From: Stephen Hemminger <shemminger@linux-foundation.org>
Message-ID: <20080311082347.0140c4d2@extreme>
In-Reply-To: <47D57881.2020503@redfish-solutions.com>
References: <47D57881.2020503@redfish-solutions.com>
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Subject: Re: [Bridge] Question about using brctl and changing MAC addresses
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To: Philip Prindeville <philipp_subx@redfish-solutions.com>
Cc: bridge@linux-foundation.org

On Mon, 10 Mar 2008 11:05:53 -0700
Philip Prindeville <philipp_subx@redfish-solutions.com> wrote:

> I'm using Linux 2.6.20 (yes, I'll be upgrading to 2.6.24 as soon as it's
> stable).
> 
> I have 4 VIA rhine ethernet controllers on my Soekris net5501, plus an
> ADSL PCI card (a Sangoma S-518) that runs in AAL5-SNAP mode, so it looks
> like an Ethernet controller.
> 
> I'm trying to bridge eth0 and w1ad (the ADSL interface) into "br0".  And
> I'm trying to force the traffic on br0 to have the MAC address that my
> ISP insists I use (i.e. that of the crappy little Westell 6100 modem
> they sent me).
> 
> The issue is the following.  If I do:
> 
> ifconfig w1ad down hw ether x:x:x:x:x:x up
> 
> followed by either:
> 
> brctl addbr br0
> brctl addif br0 eth0
> brctl addif br0 w1ad
> 
> or:
> 
> brctl addbr br0
> brctl addif br0 w1ad
> brctl addif br0 eth0
> 
> the bridge ends up taking the MAC address of eth0 either way, which I
> don't get (how does it decide which to use?).
> 
> I can clone the same MAC address to both eth0 and w1ad, but I don't know
> if that would cause me any problems or not (I haven't read the STP spec
> in about 15 years).
> 

Having the same mac address on both just is going to be problematic (impossible
to do STP), so don't if you don't have to.
But you can set address of bridge and eth0 to any address you want. So set these
to the ISP assigned address.  You probably will have to do it after bridge
is created.

brctl addbr br0
brctl addif br0 w1ad br0
ifconfig eth0 hw ether x:x:x:x:x:x up
ifconfig w1ad up
ifconfig br0 hw ether x:x:x:x:x:x up

ifconfig br0 A.B.C.D netmask 255.255.255.0