netdev - Re: Bridge connectivity interruptions while devices join or leave the bridge

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Message-ID: <20180919100755.GA26424@splinter>
Date:   Wed, 19 Sep 2018 13:07:55 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Johannes Wienke <jwienke@...hfak.uni-bielefeld.de>
Cc:     netdev@...r.kernel.org
Subject: Re: Bridge connectivity interruptions while devices join or leave
 the bridge

On Wed, Sep 19, 2018 at 11:10:22AM +0200, Johannes Wienke wrote:
> Can someone explain what is happening here and why adding and removing
> devices to a bridge results in the connectivity issues? How to avoid
> this behavior? I'd be glad for any hint on that.

The MAC address of the bridge ('brtest' in your example) is inherited
from the bridge port with the "smallest" MAC address. Thus, when you
generate veth devices with random MACs and enslave them to the bridge,
you sometimes change the bridge's MAC address as well. And since the
bridge is the default gateway sometimes packets are sent to the wrong
MAC address.

You can avoid randomly changing the bridge's MAC by setting it
explicitly:
# ip link set dev brtest address <some_mac>