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Date:      Mon, 23 Dec 2019 12:44:25 +0300
From:      "Andrey V. Elsukov" <bu7cher@yandex.ru>
To:        Victor Sudakov <vas@sibptus.ru>, freebsd-net@freebsd.org
Subject:   Re: IPSec transport mode, mtu, fragmentation...
Message-ID:  <7cc2f101-c870-c517-8e01-d656079a75be@yandex.ru>
In-Reply-To: <55eeca4c-9633-339a-f521-b0db462cc1d6@yandex.ru>
References:  <20191220152314.GA55278@admin.sibptus.ru> <f38d1f3c-dc47-0776-29f9-2151b05e09b0@tuxpowered.net> <20191220160357.GB56081@admin.sibptus.ru> <20191220162233.GA56815@admin.sibptus.ru> <55eeca4c-9633-339a-f521-b0db462cc1d6@yandex.ru>

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From: "Andrey V. Elsukov" <bu7cher@yandex.ru>
To: Victor Sudakov <vas@sibptus.ru>, freebsd-net@freebsd.org
Message-ID: <7cc2f101-c870-c517-8e01-d656079a75be@yandex.ru>
Subject: Re: IPSec transport mode, mtu, fragmentation...
References: <20191220152314.GA55278@admin.sibptus.ru>
 <f38d1f3c-dc47-0776-29f9-2151b05e09b0@tuxpowered.net>
 <20191220160357.GB56081@admin.sibptus.ru>
 <20191220162233.GA56815@admin.sibptus.ru>
 <55eeca4c-9633-339a-f521-b0db462cc1d6@yandex.ru>
In-Reply-To: <55eeca4c-9633-339a-f521-b0db462cc1d6@yandex.ru>

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On 23.12.2019 12:39, Andrey V. Elsukov wrote:
> On 20.12.2019 19:22, Victor Sudakov wrote:
>>> What's the root of the problem? ESP packets cannot get fragmented or
>>> what?=20
>>
>> Wireshark has shown that the "Don't Fragment" flag is set on all ESP
>> (protocol 50) packets. Who does this, why, and how can I switch it off=

>> globally?
>=20
> Hi,
>=20
> I think this DF flag is originally from TCP packet.
> ESP xform for transport mode just replaces protocol in IP header and
> adds some info to the end of a packet.

This is controlled by net.inet.tcp.path_mtu_discovery variable.
TCP won't set IP_DF flag if you disable this feature.

--=20
WBR, Andrey V. Elsukov


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