Date: Fri, 17 Jan 2020 22:09:28 +0700 From: Victor Sudakov <vas@sibptus.ru> To: Eugene Grosbein <eugen@grosbein.net> Cc: freebsd-net@freebsd.org, "Andrey V. Elsukov" <bu7cher@yandex.ru>, Michael Tuexen <tuexen@freebsd.org> Subject: Re: IPSec transport mode, mtu, fragmentation... Message-ID: <20200117150928.GB66677@admin.sibptus.ru> In-Reply-To: <70b0b855-189b-03c2-0712-fc1e35640702@grosbein.net> 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> <70b0b855-189b-03c2-0712-fc1e35640702@grosbein.net>
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--RASg3xLB4tUQ4RcS Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Eugene Grosbein wrote: > 17.01.2020 16:36, Victor Sudakov =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >=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. >=20 > If outgoing route (f.e. default route) has lower MTU, kernel should respo= nd with EMSGSIZE > to TCP's attempt to send oversized packet when PMTUD is enabled. >=20 > If PMTUD discovers that path mtu is low, it should store this information= in the hostcache > (see sysctl net.inet.tcp.hostcache.list) and use hostcache's MTU for same= goal. Should this result in a smaller MSS in TCP to such hosts? PS "sysctl net.inet.tcp.hostcache.list | grep 192.168.246.11" yields nothing, and yet 192.168.246.11 is the VM with which I have a transport mode SA. --=20 Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/ --RASg3xLB4tUQ4RcS Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAEBAgAGBQJeIc4oAAoJEA2k8lmbXsY0tV8H/2imb08pHf9dWZz5ssP6D9Nu 8U6UJen0w4OPqVDJ3aPp3eoetbg+twP3gIvXPpsxREq3t0VbRy6aPZlrDFT2odO2 rnrlQ9kej/2YqMfPSvhbPUqIMkTkIZX0Vfzke02uEA0gi8gsMuQQ7wYX6iHoo86W SaieSitwaxA4YjnCUse359OLffM6g06uQeWGPEIl08JpKqFb3y9e8EfuS+PcgFhN E0qR9+l15amssoGztDY1Yv/3j/Nm8Zwlv7x0NLNuXuAhpVuOSbIMozvquV+B4bKS YG2/qUXR1oN6bNREM/OLVbSZSUc5CNQE3Z3dlz1BuRlj4cTvIymbCk9LITMDvak= =V3Vg -----END PGP SIGNATURE----- --RASg3xLB4tUQ4RcS--
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