From owner-freebsd-net@freebsd.org Wed Jan 8 02:51:44 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 7C41B1F9E71 for ; Wed, 8 Jan 2020 02:51:44 +0000 (UTC) (envelope-from ryan@u13.net) Received: from vm-mx01.puttynuts.com (mail.u13.net [162.221.187.212]) by mx1.freebsd.org (Postfix) with ESMTP id 47sv0G5R0rz3ylW for ; Wed, 8 Jan 2020 02:51:42 +0000 (UTC) (envelope-from ryan@u13.net) Received: from [172.28.11.105] (unknown [205.234.176.202]) by vm-mx01.puttynuts.com (Postfix) with ESMTPSA id D85B49F0B; Wed, 8 Jan 2020 02:50:50 -0500 (EST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: ssh command hang From: Ryan Rawdon In-Reply-To: Date: Tue, 7 Jan 2020 21:51:34 -0500 Cc: freebsd-net@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: References: To: tkhemili78@outlook.com X-Mailer: Apple Mail (2.3273) X-Rspamd-Queue-Id: 47sv0G5R0rz3ylW X-Spamd-Bar: +++ Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=pass (mx1.freebsd.org: domain of ryan@u13.net designates 162.221.187.212 as permitted sender) smtp.mailfrom=ryan@u13.net X-Spamd-Result: default: False [3.64 / 15.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; R_SPF_ALLOW(-0.20)[+mx]; MV_CASE(0.50)[]; MIME_GOOD(-0.10)[text/plain]; TO_DN_NONE(0.00)[]; DMARC_NA(0.00)[u13.net]; NEURAL_SPAM_MEDIUM(0.82)[0.822,0]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; NEURAL_SPAM_LONG(0.90)[0.897,0]; IP_SCORE(1.62)[ipnet: 162.221.184.0/21(4.41), asn: 33182(3.76), country: US(-0.05)]; FREEMAIL_TO(0.00)[outlook.com]; RCVD_NO_TLS_LAST(0.10)[]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:33182, ipnet:162.221.184.0/21, country:US]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2] 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: Wed, 08 Jan 2020 02:51:44 -0000 > On Jan 7, 2020, at 3:30 PM, Bejiita78 . wrote: >=20 > has anyone ever noticed that locally a system may respond just fine, = but > running a command like port make install or top would cause the ssh = session > to hang indefinitely? This is a common sign of a MTU mismatch on a network segment somewhere = between your client and the server (large segments/packets/frames go = into a black hole and nobody knows); or the path has a = properly-configured reduced MTU, but the server is sending the traffic = with the Don=E2=80=99t Fragment bit set (IP header); but the device in = the path dropping it due to a smaller MTU is not successfully having = Packet Too Big ICMP errors get back to the server. =20 If you perform a packet capture on the server, you will likely see it = retransmitting one or more segments over and over - but not see those = arriving to the client. =20 The approach to diagnosing the point of the issue being introduced (MTU = mismatch, ICMP filtering, or the server not utilizing ICMP PTB responses = properly) depends largely on the network topology between your client = and server; and your ability to investigate or reproduce the symptoms in = systems along that path. There are plenty of other potential causes for this behavior, but this = is the first one I would investigate if experiencing this issue. Have = there been any network changes near your client or server that might = have meddled with MTU sizes or ICMP blocking?