Date: Fri, 17 Jan 2020 22:04:45 +0700 From: Victor Sudakov <vas@sibptus.ru> To: "Andrey V. Elsukov" <bu7cher@yandex.ru> Cc: Eugene Grosbein <eugen@grosbein.net>, freebsd-net@freebsd.org, Michael Tuexen <tuexen@freebsd.org> Subject: Re: IPSec transport mode, mtu, fragmentation... Message-ID: <20200117150445.GA66677@admin.sibptus.ru> In-Reply-To: <7c153a5a-db38-2770-89c7-9f95f59d29de@yandex.ru> References: <20191220152314.GA55278@admin.sibptus.ru> <4cc83b85-dd30-8c0d-330e-aa549ce98c98@yandex.ru> <f9b7357e-ced1-4ce5-40d5-8e3dcad42442@yandex.ru> <d263a709-63cf-7da5-1747-8a6791f6503f@grosbein.net> <20200116155305.GA465@admin.sibptus.ru> <55f7bafa-24c4-9810-0d21-f82cb332ee2d@grosbein.net> <20200116160745.GA1356@admin.sibptus.ru> <72355e03-1cf8-c58f-3aec-b0a21e631870@grosbein.net> <20200117093645.GA51899@admin.sibptus.ru> <7c153a5a-db38-2770-89c7-9f95f59d29de@yandex.ru>
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--bg08WKrSYDhXBjb5 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Andrey V. Elsukov wrote: > On 17.01.2020 12:36, Victor Sudakov wrote: > > Back to the point. I've figured out that both encrypted (in transport > > mode) and unencrypted TCP segments have the same MSS=3D1460. Then I'm > > completely at a loss how the encrypted packets avoid being fragmented. > > TCP has no way to know in advance that encryption overhead will be > > added. >=20 > For IPsec endpoints (i.e. when you encrypt own sessions) TCP for each > outgoing packet invokes IPSEC_HDRSIZE() method, that returns approximate > size required for IPsec, and using this information it calculates MSS.=20 I observe in Wireshark that the MSS is the same in encrypted and unencrypted segments. > I think this should work in this way. Obviouisly it is not working this way, if it were, I'd see different MSS values, but this is not the case. --=20 Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/ --bg08WKrSYDhXBjb5 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAEBAgAGBQJeIc0NAAoJEA2k8lmbXsY0Pr4IAKh6vDcxWXYVHdSw21S09UWs OEQexRibu/osY0kH1llsyZLczBoEZ3mKOW571ld7FFA7r7Scyh/KejppWYRVZTp4 1bMGwV73Zy4Z78D6FR5L/zZ5Ga6b8brj0DU4PZtKeqj5O8rdEYPFIGmB/n1GBkWr YuPqSFQtyMFwRmLvQVKGbVJmV7025yBZWx2LapVPqEjKfALHU3bKX1ELOUXOpNT5 Tf/bH4d8dow2c+/3+M7wJc+iMT1ylLwQdps1IbWXIWoTzCkn3EuI6ms3RDfej9Rp ku9ms1kfpSMUHnhuTuRTPSAUvZi1MuT8YN/7dI6qMJGp3b1zo5clxbugtyhFk5o= =Z0mt -----END PGP SIGNATURE----- --bg08WKrSYDhXBjb5--
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