Re: [Bridge] Question about using brctl and changing MAC addresses

[Philip Prindeville <philipp_subx@redfish-solutions.com>]

Andy Gospodarek wrote:
> On Wed, Mar 12, 2008 at 2:45 PM, Philip Prindeville
> <philipp_subx@redfish-solutions.com> wrote:
>   
>> Stephen Hemminger wrote:
>>  > On Wed, 12 Mar 2008 10:46:48 -0400
>>  > "Andy Gospodarek" <andy@greyhouse.net> wrote:
>>  >
>>  >
>>  >> On Tue, Mar 11, 2008 at 11:29 PM, Philip Prindeville
>>  >> <philipp_subx@redfish-solutions.com> wrote:
>>  >>
>>  >>> Stephen Hemminger wrote:
>>  >>>  > 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
>>  >>>  >
>>  >>>
>>  >>>  That seems to not work.  I get:
>>  >>>
>>  >>>  # ifconfig br0 hw ether "00:18:3A:55:15:35"
>>  >>>
>>  >>> ifconfig: SIOCSIFHWADDR: Cannot assign requested address
>>  >>>  #
>>  >>>
>>  >>>  Any ideas why?  I'm doing this before an IP address has even been
>>  >>>  assigned...
>>  >>>
>>  >
>>  > Assign the hardware address of the bridge was only added in later kernels.
>>  >
>>
>>  Later being which kernel?
>>     
>
> It looks like this commit did it:
>
> commit 4505a3ef720845b5db3ddb440de13cd4800fd508
> Author: Stephen Hemminger <shemminger@osdl.org>
> Date:   Wed Dec 21 18:51:49 2005 -0800
>
>     [BRIDGE]: allow setting hardware address of bridge pseudo-dev
>
>     Some people are using bridging to hide multiple machines from an ISP
>     that restricts by MAC address. So in that case allow the bridge mac
>     address to be set to any of the existing interfaces.  I don't want to
>     allow any arbitrary value and confuse STP.
>
>     Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
>     Signed-off-by: David S. Miller <davem@davemloft.net>
>
> So that should mean it is in 2.6.15 and later (presuming this patch
> added all the needed functionality).
>   

Well, I don't get it then.

I'm running Linux 2.6.20, with bridge-utils-1.2, and I'm still seeing it.

Can you send me the link to the patch, and I'll make sure it's in my 
sources?

Thanks,

-Philip


>   
>>  And to answer the earlier question, I was doing:
>>
>>  ifconfig brX down hw ether x:x:x:x:x:x up
>>
>>  so yes, the interface was down when I tried to change its address.
>>
>>  -Philip
>>
>>
>>
>>