netdev - Re: [BUG] bonded interfaces drop bpdu (stp) frames

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Message-ID: <CAF2d9jjXmiVZwDu-q+M5bmdrgyMr0U_tiUzxoCUiWwZT4NS5Cw@mail.gmail.com>
Date:   Thu, 12 Jul 2018 14:26:44 -0700
From:   Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     Michal Soltys <soltys@....info>,
        Chonggang Li <chonggangli@...gle.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [BUG] bonded interfaces drop bpdu (stp) frames

On Thu, Jul 12, 2018 at 11:03 AM, Jay Vosburgh
<jay.vosburgh@...onical.com> wrote:
> Michal Soltys <soltys@....info> wrote:
>
>>On 07/12/2018 04:51 PM, Jay Vosburgh wrote:
>>> Mahesh Bandewar (महेश बंडेवार) wrote:
>>>
>>>> On Wed, Jul 11, 2018 at 3:23 PM, Michal Soltys <soltys@....info> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> 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).
>>>>>
>>>> I believe these are link-local-multicast messages and sometime back a
>>>> change went into to not pass those frames to the bonding master. This
>>>> could be the side effect of that.
>>>
>>>      Mahesh, I suspect you're thinking of:
>>>
>>> commit b89f04c61efe3b7756434d693b9203cc0cce002e
>>> Author: Chonggang Li <chonggangli@...gle.com>
>>> Date:   Sun Apr 16 12:02:18 2017 -0700
>>>
>>>      bonding: deliver link-local packets with skb->dev set to link that packets arrived on
>>>
>>>      Michal, are you able to revert this patch and test?
>>>
>>>      -J
>>>
>>> ---
>>>      -Jay Vosburgh, jay.vosburgh@...onical.com
>>>
>>
>>
>>Just tested - yes, reverting that patch solves the issues.
>
>         Chonggang,
>
>         Reading the changelog in your commit referenced above, I'm not
> entirely sure what actual problem it is fixing.  Could you elaborate?
>
>         As the patch appears to cause a regression, it needs to be
> either fixed or reverted.
>
>         Mahesh, you signed-off on it as well, perhaps you also have some
> context?
>

I think the original idea behind it was to pass the LLDPDUs to the
stack on the interface that they came on since this is considered to
be link-local traffic and passing to bond-master would loose it's
"linklocal-ness". This is true for LLDP and if you change the skb->dev
of the packet, then you don't know which slave link it came on in
(from LLDP consumer's perspective).

I don't know much about STP but trunking two links and aggregating
this link info through bond-master seems wrong. Just like LLDP, you
are losing info specific to a link and the decision derived from that
info could be wrong.

Having said that, we determine "linklocal-ness" by looking at L2 and
bondmaster shares this with lts slaves. So it does seem fair to pass
those frames to the bonding-master but at the same time link-local
traffic is supposed to be limited to the physical link (LLDP/STP/LACP
etc). Your thoughts?


>         -J
>
> ---
>         -Jay Vosburgh, jay.vosburgh@...onical.com