From owner-freebsd-net@freebsd.org Fri Jan 17 15:38:09 2020 Return-Path: Delivered-To: freebsd-net@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 92A9C1F17F8 for ; Fri, 17 Jan 2020 15:38:09 +0000 (UTC) (envelope-from eugen@grosbein.net) Received: from hz.grosbein.net (hz.grosbein.net [IPv6:2a01:4f8:c2c:26d8::2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "hz.grosbein.net", Issuer "hz.grosbein.net" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 47zlZT09bXz4ctn; Fri, 17 Jan 2020 15:38:08 +0000 (UTC) (envelope-from eugen@grosbein.net) Received: from eg.sd.rdtc.ru (eg.sd.rdtc.ru [IPv6:2a03:3100:c:13:0:0:0:5]) by hz.grosbein.net (8.15.2/8.15.2) with ESMTPS id 00HFbvcm045698 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 17 Jan 2020 15:37:58 GMT (envelope-from eugen@grosbein.net) X-Envelope-From: eugen@grosbein.net X-Envelope-To: vas@sibptus.ru Received: from [10.58.0.4] ([10.58.0.4]) by eg.sd.rdtc.ru (8.15.2/8.15.2) with ESMTPS id 00HFbuCC045220 (version=TLSv1.2 cipher=DHE-RSA-AES128-SHA bits=128 verify=NOT); Fri, 17 Jan 2020 22:37:56 +0700 (+07) (envelope-from eugen@grosbein.net) Subject: Re: IPSec transport mode, mtu, fragmentation... To: Victor Sudakov References: <20191220152314.GA55278@admin.sibptus.ru> <4cc83b85-dd30-8c0d-330e-aa549ce98c98@yandex.ru> <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> Cc: freebsd-net@freebsd.org, "Andrey V. Elsukov" , Michael Tuexen From: Eugene Grosbein Message-ID: <16550199-67b9-d331-0c1e-4afa0e8b361c@grosbein.net> Date: Fri, 17 Jan 2020 22:37:50 +0700 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20200117150928.GB66677@admin.sibptus.ru> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=0.3 required=5.0 tests=BAYES_00,LOCAL_FROM, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.2 X-Spam-Report: * -2.3 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record * -0.0 SPF_PASS SPF: sender matches SPF record * 2.6 LOCAL_FROM From my domains X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on hz.grosbein.net X-Rspamd-Queue-Id: 47zlZT09bXz4ctn X-Spamd-Bar: --- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=permerror (mx1.freebsd.org: domain of eugen@grosbein.net uses mechanism not recognized by this client) smtp.mailfrom=eugen@grosbein.net X-Spamd-Result: default: False [-3.87 / 15.00]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-0.999,0]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; TO_DN_SOME(0.00)[]; NEURAL_HAM_LONG(-1.00)[-0.998,0]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[grosbein.net]; RCVD_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_SOME(0.00)[]; R_SPF_PERMFAIL(0.00)[]; IP_SCORE(-1.77)[ip: (-4.84), ipnet: 2a01:4f8::/29(-2.49), asn: 24940(-1.52), country: DE(-0.02)]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:24940, ipnet:2a01:4f8::/29, country:DE]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[] X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 17 Jan 2020 15:38:09 -0000 17.01.2020 22:09, 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=1460. 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. >> >> If outgoing route (f.e. default route) has lower MTU, kernel should respond with EMSGSIZE >> to TCP's attempt to send oversized packet when PMTUD is enabled. >> >> 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. I guess that Path MTU in such case is 1500, so PMTUD won't help here.