Date: Sat, 18 Jan 2020 06:44:56 -0800 From: Michael Sierchio <kudzu@tenebras.com> To: Eugene Grosbein <eugen@grosbein.net> Cc: Victor Sudakov <vas@sibptus.ru>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, "Andrey V. Elsukov" <bu7cher@yandex.ru>, Michael Tuexen <tuexen@freebsd.org> Subject: Re: IPSec transport mode, mtu, fragmentation... Message-ID: <CAHu1Y71hGwPP48nYUYUpKQO3r%2B8HwEWq4uNGOi3Bup3PuC%2BYZA@mail.gmail.com> In-Reply-To: <d59805e9-3fd5-eb56-10db-26b532cb5e85@grosbein.net> References: <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> <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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[apologies for top-posting] What is the result of > sysctl net.enc ? This might be a clue about the packets, which you could be seeing twice. On Sat, Jan 18, 2020 at 3:17 AM Eugene Grosbein <eugen@grosbein.net> wrote: > 18.01.2020 17:55, Victor Sudakov wrote: > > >>>>> 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 > fragmented. > >>>>> TCP has no way to know in advance that encryption overhead will be > >>>>> added. > > > > Here: http://admin.sibptus.ru/~vas/ftp-pcap.tar.gz you can find two > > identical FTP sessions, the only difference being ipsec=3Doff during on= e > > session and ipsec=3Don during the other one. > > > > 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. > > > > 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 yo= u > > explain this? There are almost no retransmissions in the unencrypted > session. > > > > 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. > > > > Could the retransmissions be some artifact of the enc(4) interface I wa= s > > capturing the encrypted session on? > > I doubt it. And I can't explain this, but maybe it's work of PMTUD > Blackhole detection? > Look at sysctl net.inet.tcp | fgrep blackhole_ > > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" > --=20 "Well," Brahm=C4=81 said, "even after ten thousand explanations, a fool is = no wiser, but an intelligent person requires only two thousand five hundred." - The Mah=C4=81bh=C4=81rata
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