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

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

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?

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