[Bridge] Bridge interface always down since Linux >= 2.6.39
Stephen Hemminger
shemminger at linux-foundation.org
Thu Jun 30 09:22:58 PDT 2011
On Thu, 30 Jun 2011 15:05:36 +0200
Arnaud Fontaine <arnau at milkypond.org> wrote:
> Hello,
>
> After upgrading my kernel to 2.6.39 (I also tested with 3.0.0-rc4), my
> bridge interface with only TAP interfaces is always down (the flag is
> NO_CARRIER and operational state is DOWN) despite it was working well
> with previous versions of the kernel (the state was LOWER_UP and
> operational state was UNKNOWN). Before, running the following commands
> was enough to activate the bridge interface:
>
> 1. brctl addbr br0
> 2. ip link set br0 up
>
> Only by attaching a real network interface (such as eth0) to the bridge,
> it finally works well but I would like to be able to not only use real
> network interfaces.
>
> Any idea? Many thanks in advance.
>
> Regards,
There are two flags, IFF_UP - admin up/down and IFF_RUNNING carrier up/down
The IFF_UP is controlled manually, and IFF_RUNNING is what you are talking
about.
In older kernel versions, the bridge device always asserted carrier even
if all ports did not have carrier. Now it reflects the state of the underlying
device. In your case the problem is that the tap interfaces aren't reporting
carrier.
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