netdev - Re: Silently dropped UDP packets on kernel 4.14

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Message-ID: <CAKfDRXhW=pN+uMggpJqk2PPHGcEHhoRT-Dr_T-B_sNghRTNiow@mail.gmail.com>
Date:   Thu, 3 May 2018 13:19:49 +0200
From:   Kristian Evensen <kristian.evensen@...il.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Florian Westphal <fw@...len.de>,
        Netfilter Development Mailing list 
        <netfilter-devel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: Silently dropped UDP packets on kernel 4.14

Hi Michal,

Thanks for providing a nice summary of your experience when dealing
with this problem. Always nice to know that I am not alone :)

On Thu, May 3, 2018 at 11:42 AM, Michal Kubecek <mkubecek@...e.cz> wrote:
> One of the ideas I had was this:
>
>   - keep also unconfirmed conntracks in some data structure
>   - check new packets also against unconfirmed conntracks
>   - if it matches an unconfirmed conntrack, defer its processing
>     until that conntrack is either inserted or discarded

I was thinking about something along the same lines and came to the
same conclusion, it is a lot of hassle and work for a very special
case. I think that replacing the conntrack entry is a good compromise,
it improves on the current situation, and allows for the creation of
"perfect" solutions in user-space. For example, a user can keep track
of seen UDP flows, and then only release new packets belonging to the
same flow when the conntrack entry is created.

BR,
Kristian