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Date:   Thu, 12 Jul 2018 00:23:59 +0200
From:   Michal Soltys <>
Subject: [BUG] bonded interfaces drop bpdu (stp) frames


As weird as that sounds, this is what I observed today after bumping
kernel version. I have a setup where 2 bonds are attached to linux
bridge and physically are connected to two switches doing MSTP (and
linux bridge is just passing them).

Initially I suspected some changes related to bridge code - but quick
peek at the code showed nothing suspicious - and the part of it that
explicitly passes stp frames if stp is not enabled has seen little
changes (e.g. per-port group_fwd_mask added recently). Furthermore - if
regular non-bonded interfaces are attached everything works fine.

Just to be sure I detached the bond (802.3ad mode) and checked it with
simple tcpdump (ether proto \\stp) - and indeed no hello packets were
there (with them being present just fine on active enslaved interface,
or on the bond device in earlier kernels).

If time permits I'll bisect tommorow to pinpoint the commit, but from
quick todays test - 4.9.x is working fine, while 4.16.16 (tested on
debian) and 4.17.3 (tested on archlinux) are failing.

Unless this is already a known issue (or you have any suggestions what
could be responsible).

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