Date: Sat, 18 Jan 2020 18:50:04 +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: <20200118115004.GA13555@admin.sibptus.ru> In-Reply-To: <d59805e9-3fd5-eb56-10db-26b532cb5e85@grosbein.net> References: <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> <20200117150928.GB66677@admin.sibptus.ru> <16550199-67b9-d331-0c1e-4afa0e8b361c@grosbein.net> <20200118105524.GA10042@admin.sibptus.ru> <d59805e9-3fd5-eb56-10db-26b532cb5e85@grosbein.net>
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--6TrnltStXW4iwmi0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Eugene Grosbein wrote: >=20 > >>>>> Back to the point. I've figured out that both encrypted (in transpo= rt > >>>>> mode) and unencrypted TCP segments have the same MSS=3D1460. Then I= 'm > >>>>> completely at a loss how the encrypted packets avoid being fragment= ed. > >>>>> TCP has no way to know in advance that encryption overhead will be > >>>>> added. > >=20 > > Here: http://admin.sibptus.ru/~vas/ftp-pcap.tar.gz you can find two > > identical FTP sessions, the only difference being ipsec=3Doff during one > > session and ipsec=3Don during the other one. > >=20 > > As I said, in both the sessions MSS=3D1460 which is already odd, and I > > can't explain to myself why file transfer still works without MSS > > ajustment. > >=20 > > Moreover, something fishy is happening in the encrypted session: there > > are many TCP retransmissions (I was capturing on the FTP server's side, > > so there are many segments with the same sequence number). How would you > > explain this? There are almost no retransmissions in the unencrypted se= ssion. > >=20 > > All this is happening in a lab environment (one bhyve VM is an FTP > > server and the other downloads a file from the first), both VMs are on > > the same bridge interface. There are almost 19,000 packets in the > > encrypted file vs 12,000 in the plain file, I think because of those > > excessive retransmissions. > >=20 > > Could the retransmissions be some artifact of the enc(4) interface I was > > capturing the encrypted session on? >=20 > I doubt it. And I can't explain this,=20 But do you agree that the traffic dumps contain an anomaly? > but maybe it's work of PMTUD Blackhole detection? > Look at sysctl net.inet.tcp | fgrep blackhole_ On both 192.168.246.10 and 192.168.246.11: root@fbsd-test1:~vas # sysctl net.inet.tcp | fgrep blackhole_ net.inet.tcp.v6pmtud_blackhole_mss: 1220 net.inet.tcp.pmtud_blackhole_mss: 1200 net.inet.tcp.pmtud_blackhole_detection: 0 root@fbsd-test2:~ # sysctl net.inet.tcp | fgrep blackhole_ net.inet.tcp.v6pmtud_blackhole_mss: 1220 net.inet.tcp.pmtud_blackhole_mss: 1200 net.inet.tcp.pmtud_blackhole_detection: 0 root@fbsd-test2:~ #=20 --=20 Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/ --6TrnltStXW4iwmi0 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAEBAgAGBQJeIvDsAAoJEA2k8lmbXsY0Pc0H/RCJZvdb3hgIRoVZlBZwD15F 6Xco2+ji/pf9LstucIjPzZXBIjjBLbkn7aAb7lADXE0e7vXzFLFNzxSDiB6LTCfB xzrjvAbPMaeQX/Bg2SPl3GlzGkorQRDEkgp5RsbTX2YUIwBzovooiSduFdNPt/8g ET9bF2d03i0DoDS8Kp0OT+RTaFpZ/u+B5p59rhCUR0cM88PmkETX3OjXeWH/WSF8 RMDH80yT19NeEa8oCke1dMf2UmL3KPpKhxuxq+iclfs4KRliq0ngREvdn3hK5jf9 khKlVWJRFkuwVwXasmop+OTsBUkQkX99m3jpoyvpLSSqrUwixUss+dDgWLlFZ/k= =Tlj/ -----END PGP SIGNATURE----- --6TrnltStXW4iwmi0--
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