From owner-freebsd-bugs@freebsd.org Fri Aug 9 18:40:03 2019 Return-Path: Delivered-To: freebsd-bugs@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 BE58CCEB61 for ; Fri, 9 Aug 2019 18:40:03 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mailman.nyi.freebsd.org (mailman.nyi.freebsd.org [IPv6:2610:1c1:1:606c::50:13]) by mx1.freebsd.org (Postfix) with ESMTP id 464vDg4d8zz3NLh for ; Fri, 9 Aug 2019 18:40:03 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: by mailman.nyi.freebsd.org (Postfix) id 9D04ECEB60; Fri, 9 Aug 2019 18:40:03 +0000 (UTC) Delivered-To: bugs@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 9BA17CEB5F for ; Fri, 9 Aug 2019 18:40:03 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 464vDg3b1hz3NLf for ; Fri, 9 Aug 2019 18:40:03 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2610:1c1:1:606c::50:1d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 58E4F19D64 for ; Fri, 9 Aug 2019 18:40:03 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.5]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id x79Ie3Y1021888 for ; Fri, 9 Aug 2019 18:40:03 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id x79Ie3UC021887 for bugs@FreeBSD.org; Fri, 9 Aug 2019 18:40:03 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 239749] Issues path MTU discovery on IPv6 and SSH. Date: Fri, 09 Aug 2019 18:40:03 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: zeising@FreeBSD.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 09 Aug 2019 18:40:03 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D239749 Bug ID: 239749 Summary: Issues path MTU discovery on IPv6 and SSH. Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: zeising@FreeBSD.org There seem to be an issue with path MTU discovery, and SSH (and possibly others). I have a FreeBSD router, running 12.0-RELEASE-p9. The router terminates an IPv6 tunnel, using gif (protocol 41). The MTU on the tunnel is 1480, becau= se of the encapsulating IPv4 header. In my internal network, the MTU is the standard 1500. >From my work station, when I try to SSH over IPv6 to, for example freefall.freebsd.org, the connection fails. I can see in package dumps that the router responds with an ICMP packet too big. I can understand that thi= s is the case for the first attempt since the local link has an MTU of 1500 but = the remote link has an MTU of 1480, but ssh does multiple attempts with the same packet size, and gets ICMP ptb in return. Eventually, the connection is re= set. I expected that something, either in our TCP stack, IP stack or in SSH, wou= ld adjust to the lower MTU, and resend a shorter packet (possibly splitting it= in multiple TCP packets). After the first SSH connection attempt has failed, if I try again, the connection succeeds, so something adjusts so that later connections are not using the too big MTU. I have a packet capture of the traffic between my work station, router and freefall.freebsd.org, that hopefully can shed a little bit of light on what= 's going on. It's available on request. --=20 You are receiving this mail because: You are the assignee for the bug.=