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Date:   Sat, 2 Apr 2022 23:51:35 +0200
From:   Jaco Kroon <>
To:     Florian Westphal <>
Cc:     Neal Cardwell <>,
        Eric Dumazet <>,
        LKML <>,
        Netdev <>,
        Yuchung Cheng <>, Wei Wang <>
Subject: Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP

Hi Florian,

On 2022/04/02 16:14, Florian Westphal wrote:
> Jaco Kroon <> wrote:
>> Including sysctl net.netfilter.nf_conntrack_log_invalid=6- which
>> generates lots of logs, something specific I should be looking for?  I
>> suspect these relate:
>> [Sat Apr  2 10:31:53 2022] nf_ct_proto_6: SEQ is over the upper bound
>> (over the window of the receiver) IN= OUT=bond0
>> SRC=2c0f:f720:0000:0003:d6ae:52ff:feb8:f27b
>> DST=2a00:1450:400c:0c08:0000:0000:0000:001a LEN=2928 TC=0 HOPLIMIT=64
>> FLOWLBL=867133 PROTO=TCP SPT=48920 DPT=25 SEQ=2689938314 ACK=4200412020
>> WINDOW=447 RES=0x00 ACK PSH URGP=0 OPT (0101080A2F36C1C120EDFB91) UID=8
>> GID=12
> I thought this had "liberal mode" enabled for tcp conntrack?
> The above implies its off.

We have liberal on the core firewalls, not on the endpoints ... yes, we
do double firewall :).

So the firewalls into the subnets has liberal mode (which really was an
oversight when axing conntrackd), but the servers themselves do not.

Kind Regards,

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