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Date:   Fri, 1 Apr 2022 02:15:31 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Eric Dumazet <edumazet@google.com>
Cc:     Jaco Kroon <jaco@uls.co.za>, Neal Cardwell <ncardwell@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>,
        Yuchung Cheng <ycheng@google.com>
Subject: Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP
 connections
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Eric Dumazet <edumazet@google.com> wrote:
> Next step would be to attempt removing _all_ firewalls, especially not
> common setups like yours.
> 
> conntrack had a bug preventing TFO deployment for a while, because
> many boxes kept buggy kernel versions for years.
> 
> 356d7d88e088687b6578ca64601b0a2c9d145296 netfilter: nf_conntrack: fix
> tcp_in_window for Fast Open

Jaco could also try with
net.netfilter.nf_conntrack_tcp_be_liberal=1

and, if that helps, with liberal=0 and
sysctl net.netfilter.nf_conntrack_log_invalid=6

(check dmesg/syslog/nflog).