Package: bridge-utils
Version: 1.7-1
Severity: serious

Dear Maintainer,

   * What led up to the situation?

Having 2 tiny servers (APU2.C4 and APU.2D4) in my local net each having
3 ethernet interfaces assigned to a bridge "br0" (configured in 
/etc/network/interfaces).
Upgrading from Bustser to Bullseye worked fine for the first box, the bridge
received a new MAC assigned by the kernel as described in the listchanges.
After reconfiguring that in the roter everything was working as before.

Upgrading the second box in the same network segment lead to almost complete
blocking of traffic in my local network and the 2nd box was not detected by the 
router.
Connecting via serial console and checking network setup revealed:

The second box got precisely the SAME MAC address as the first box!

After using bridge_hw to assign the old MAC based on the MAC of one interface 
solved the problem.

Conclusion is that hardware addresses should be unique in general, but the
current way generates same address also if the MAC's of involved interfaces 
differs - see here:

apu     enp1s0          00:0d:b9:47:83:e8               -       (Eth1)
        enp2s0          00:0d:b9:47:83:e9               -       (Eth2)
        enp3s0          00:0d:b9:47:83:ea               -       (Eth3)
        br0             00:0d:b9:47:83:e8 => 4a:0f:ba:96:49:a5

apu2    enp1s0          00:0d:b9:4e:76:a0               -       (Eth1)
        enp2s0          00:0d:b9:4e:76:a1               -       (Eth2)
        enp3s0          00:0d:b9:4e:76:a2               -       (Eth3)
        br0             00:0d:b9:4e:76:a0 => 4a:0f:ba:96:49:a5


-- System Information:
Debian Release: 11.1
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.10.0-9-amd64 (SMP w/4 CPU threads)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_US:en
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages bridge-utils depends on:
ii  libc6  2.31-13+deb11u2

bridge-utils recommends no packages.

Versions of packages bridge-utils suggests:
ii  ifupdown  0.8.36

-- no debconf information

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