Date: Sun, 19 Jan 2020 10:38:43 +0700 From: Victor Sudakov <vas@sibptus.ru> To: Julian Elischer <julian@freebsd.org> Cc: Eugene Grosbein <eugen@grosbein.net>, freebsd-net@freebsd.org, "Andrey V. Elsukov" <bu7cher@yandex.ru>, Michael Tuexen <tuexen@freebsd.org> Subject: Re: IPSec transport mode, mtu, fragmentation... Message-ID: <20200119033843.GB54797@admin.sibptus.ru> In-Reply-To: <c7f5828b-3678-b432-47a8-75afada5bd9e@freebsd.org> References: <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> <70b0b855-189b-03c2-0712-fc1e35640702@grosbein.net> <c7f5828b-3678-b432-47a8-75afada5bd9e@freebsd.org>
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--QTprm0S8XgL7H0Dt Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Julian Elischer wrote: > >=20 > > > 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. > Using multiple routing tables we could add a mechanism to the ipsec > code so that encapsulated sessions are referred to one routing table > and that the "envelope" routes are referencing another (specified in > ipsec setup) routing table.=A0 The two routing tables would have different > MTUs.=A0 This mechanism/framework would also be useful for other > tunneling protocols in general. I think before inventing something so innovative and clever, we should look at how IPSec transport mode and MTU adjustment is implemented in other OSes (OpenBSD, Linux, even Windows). Any experts? --=20 Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/ --QTprm0S8XgL7H0Dt Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAEBAgAGBQJeI89DAAoJEA2k8lmbXsY0TIQH/0vVBsG4TXRkaqmg5S9IvTR4 NjBADwPE7D+zU6yQy9Gt0GMY+Pm64iIhU/zejBhdd/Qx8aB9O+QRMY4oofi+2p7Y QeIoXn1mm6WeqOr9u4kXWFIl1k73kQw77k9t1QGBKIB8hA/J/tvYBSBBkUSwqx7a w5hLS4yMOLg8zygDg61StE9lI9rbKmDjyYpwn7iZzAECYKw4YfhTiaAi1u8gSz/e FGPRtkztKAAqcIBboTkB3KUP4G0snee4WpKrU4Y4Y23OEo3GcUZC8d6P2/yYAiAz DFT9iGnZADHpcPM+0S4r9efedT9uum9cTYvxdhEJiIuyJto8I6CZJHR3tOdbIEo= =hY+L -----END PGP SIGNATURE----- --QTprm0S8XgL7H0Dt--
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