netdev - Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP connections

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Date:   Thu, 31 Mar 2022 17:10:13 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jaco Kroon <jaco@....co.za>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP connections

On Thu, Mar 31, 2022 at 4:06 PM Jaco Kroon <jaco@....co.za> wrote:
>
> Hi Neal,
>
> This sniff was grabbed ON THE CLIENT HOST.  There is no middlebox or
> anything between the sniffer and the client.  Only the firewall on the
> host itself, where we've already establish the traffic is NOT DISCARDED
> (at least not in filter/INPUT).
>
> Setup on our end:
>
> 2 x routers, usually each with a direct peering with Google (which is
> being ignored at the moment so instead traffic is incoming via IPT over DD).
>
> Connected via switch to
>
> 2 x firewalls, of which ONE is active (they have different networks
> behind them, and could be active / standby for different networks behind
> them - avoiding active-active because conntrackd is causing more trouble
> than it's worth), Linux hosts, using netfilter, has been operating for
> years, no recent kernel upgrades.

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