[Bridge] Prevent MAC address from changing

[Bridge] Prevent MAC address from changing

[Simon Detheridge]

Hello,

I have a box with a bridge, br0, that exists to bridge a bunch of tap interfaces together. I'm running a program that binds to this address to serve things. Unfortunately, this server (it's isc-dhcp3) doesn't like it when the mac address changes.

I've tried configuring a dummy interface dummy0, and adding it as the first interface on br0, before I bind my server to it. I was hoping that the mac address of dummy0 would be used as the mac address for br0.

What actually happens is that it uses the dummy0 mac address until the first tap interface is connected, and then the mac address changes to that of the tap interface, and my dhcp server stops working.

Is there a way I can prevent this from happening?

Thanks,
Simon

-- 
Simon Detheridge - CTO, Widgit Software
26 Queen Street, Cubbington, CV32 7NA - Tel: +44 (0)1926 333680

Re: [Bridge] Prevent MAC address from changing

[Stephen Hemminger]

On Mon, 12 Jan 2009 16:05:45 +0000 (GMT)
Simon Detheridge <simon@widgit.com> wrote:

> Hello,
> 
> I have a box with a bridge, br0, that exists to bridge a bunch of tap interfaces together. I'm running a program that binds to this address to serve things. Unfortunately, this server (it's isc-dhcp3) doesn't like it when the mac address changes.
> 
> I've tried configuring a dummy interface dummy0, and adding it as the first interface on br0, before I bind my server to it. I was hoping that the mac address of dummy0 would be used as the mac address for br0.
> 
> What actually happens is that it uses the dummy0 mac address until the first tap interface is connected, and then the mac address changes to that of the tap interface, and my dhcp server stops working.
> 
> Is there a way I can prevent this from happening?
> 
> Thanks,
> Simon
> 

latest kernels have a way to set mac address. After setting mac address of bridge device,
then address won't change.  

Re: [Bridge] Prevent MAC address from changing

[Dietmar Maurer]

> latest kernels have a way to set mac address. After setting mac
address
> of bridge device, then address won't change.

AFAIK the bridge code always uses the lowest MAC address, so setting the
MAC address
does not help. As soon as you add a port with a lower MAC the address 
changes. Or did that behavior change recently?

- Dietmar

Re: [Bridge] Prevent MAC address from changing

[Stephen Hemminger]

On Mon, 12 Jan 2009 20:51:14 +0100
"Dietmar Maurer" <dietmar@proxmox.com> wrote:

> > latest kernels have a way to set mac address. After setting mac
> address
> > of bridge device, then address won't change.
> 
> AFAIK the bridge code always uses the lowest MAC address, so setting the
> MAC address
> does not help. As soon as you add a port with a lower MAC the address 
> changes. Or did that behavior change recently?
> 
> - Dietmar
> 

If you manually configure an MAC address, it sticks as of 2.6.27

Re: [Bridge] Prevent MAC address from changing

[Simon Detheridge]

----- "Stephen Hemminger" <shemminger@vyatta.com> wrote:

> If you manually configure an MAC address, it sticks as of 2.6.27

*sigh* - This was what I tried to do, but it didn't work. Obviously my kernel is too old.

I'm on Amazon EC2, which is stuck on 2.6.21 right now (at least in Europe, which is where I'm trying to host my application). 

I tried listening on dummy0 instead, but it turns out a dummy interface is not a real interface and my packets go nowhere. 

veth might be perfect for what I'm trying to do (it makes a bit more sense than an IP address assigned to the bridge) but again my kernel is too old.

None of these issues are a problem for this list, however.

Thanks for the help,
Simon

-- 
Simon Detheridge - CTO, Widgit Software
26 Queen Street, Cubbington, CV32 7NA - Tel: +44 (0)1926 333680