From nobody Wed Jun 9 09:22:55 2021 X-Original-To: freebsd-current@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id DD6B611CB84E for ; Wed, 9 Jun 2021 09:22:59 +0000 (UTC) (envelope-from tuexen@freebsd.org) Received: from drew.franken.de (mail-n.franken.de [193.175.24.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.franken.de", Issuer "Sectigo RSA Domain Validation Secure Server CA" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4G0M8g584Lz3mHS; Wed, 9 Jun 2021 09:22:59 +0000 (UTC) (envelope-from tuexen@freebsd.org) Received: from smtpclient.apple (unknown [212.201.121.94]) (Authenticated sender: macmic) by mail-n.franken.de (Postfix) with ESMTPSA id 1DF087220C6D0; Wed, 9 Jun 2021 11:22:56 +0200 (CEST) Content-Type: text/plain; charset=us-ascii List-Id: Discussions about the use of FreeBSD-current List-Archive: https://lists.freebsd.org/archives/freebsd-current List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-current@freebsd.org Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) Subject: Re: ssh connections break with "Fssh_packet_write_wait" on 13 [SOLVED] From: tuexen@freebsd.org In-Reply-To: Date: Wed, 9 Jun 2021 11:22:55 +0200 Cc: Michael Gmelin , "freebsd-current@freebsd.org" Content-Transfer-Encoding: 7bit Message-Id: <7104A202-13F6-451B-85C3-74A0D7EE66D4@freebsd.org> References: <20210601134747.40920d51@bsd64.grem.de> <20210603150906.48cbd638@bsd64.grem.de> <20210608224725.35930d70@bsd64.grem.de> To: Don Lewis X-Mailer: Apple Mail (2.3654.100.0.2.22) X-Spam-Status: No, score=-2.9 required=5.0 tests=ALL_TRUSTED,BAYES_00 autolearn=disabled version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on mail-n.franken.de X-Rspamd-Queue-Id: 4G0M8g584Lz3mHS X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-ThisMailContainsUnwantedMimeParts: N > On 9. Jun 2021, at 08:57, Don Lewis wrote: > > On 8 Jun, Michael Gmelin wrote: >> >> >> On Thu, 3 Jun 2021 15:09:06 +0200 >> Michael Gmelin wrote: >> >>> On Tue, 1 Jun 2021 13:47:47 +0200 >>> Michael Gmelin wrote: >>> >>>> Hi, >>>> >>>> Since upgrading servers from 12.2 to 13.0, I get >>>> >>>> Fssh_packet_write_wait: Connection to 1.2.3.4 port 22: Broken pipe >>>> >>>> consistently, usually after about 11 idle minutes, that's with and >>>> without pf enabled. Client (11.4 in a VM) wasn't altered. >>>> >>>> Verbose logging (client and server side) doesn't show anything >>>> special when the connection breaks. In the past, QoS problems >>>> caused these disconnects, but I didn't see anything apparent >>>> changing between 12.2 and 13 in this respect. >>>> >>>> I did a test on a newly commissioned server to rule out other >>>> factors (so, same client connections, some routes, same >>>> everything). On 12.2 before the update: Connection stays open for >>>> hours. After the update (same server): connections breaks >>>> consistently after < 15 minutes (this is with unaltered >>>> configurations, no *AliveInterval configured on either side of the >>>> connection). >>> >>> I did a little bit more testing and realized that the problem goes >>> away when I disable "Proportional Rate Reduction per RFC 6937" on the >>> server side: >>> >>> sysctl net.inet.tcp.do_prr=0 >>> >>> Keeping it on and enabling net.inet.tcp.do_prr_conservative doesn't >>> fix the problem. >>> >>> This seems to be specific to Parallels. After some more digging, I >>> realized that Parallels Desktop's NAT daemon (prl_naptd) handles >>> keep-alive between the VM and the external server on its own. There is >>> no direct communication between the client and the server. This means: >>> >>> - The NAT daemon starts sending keep-alive packages right away (not >>> after the VM's net.inet.tcp.keepidle), every 75 seconds. >>> - Keep-alive packages originating in the VM never reach the server. >>> - Keep-alive originating on the server never reaches the VM. >>> - Client and server basically do keep-alive with the nat daemon, not >>> with each other. >>> >>> It also seems like Parallels is filtering the tos field (so it's >>> always 0x00), but that's unrelated. >>> >>> I configured a bhyve VM running FreeBSD 11.4 on a separate laptop on >>> the same network for comparison and is has no such issues. >>> >>> Looking at TCP dump output on the server, this is what a keep-alive >>> package sent by Parallels looks like: >>> >>> 10:14:42.449681 IP (tos 0x0, ttl 64, id 15689, offset 0, flags >>> [none], proto TCP (6), length 40) >>> 192.168.1.1.58222 > 192.168.1.2.22: Flags [.], cksum x (correct), >>> seq 2534, ack 3851, win 4096, length 0 >>> >>> While those originating from the bhyve VM (after lowering >>> net.inet.tcp.keepidle) look like this: >>> >>> 12:18:43.105460 IP (tos 0x0, ttl 62, id 0, offset 0, flags [DF], >>> proto TCP (6), length 52) >>> 192.168.1.3.57555 > 192.168.1.2.22: Flags [.], cksum x >>> (correct), seq 1780337696, ack 45831723, win 1026, options >>> [nop,nop,TS val 3003646737 ecr 3331923346], length 0 >>> >>> Like written above, once net.inet.tcp.do_prr is disabled, keepalive >>> seems to be working just fine. Otherwise, Parallel's NAT daemon kills >>> the connection, as its keep-alive requests are not answered (well, >>> that's what I think is happening): >>> >>> 10:19:43.614803 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], >>> proto TCP (6), length 40) >>> 192.168.1.1.58222 > 192.168.1.2.22: Flags [R.], cksum x (correct), >>> seq 2535, ack 3851, win 4096, length 0 >>> >>> The easiest way to work around the problem Client side is to configure >>> ServerAliveInterval in ~/.ssh/config in the Client VM. >>> >>> I'm curious though if this is basically a Parallels problem that has >>> only been exposed by PRR being more correct (which is what I suspect), >>> or if this is actually a FreeBSD problem. >>> >> >> So, PRR probably was a red herring and the real reason that's happening >> is that FreeBSD (since version 13[0]) by default discards packets >> without timestamps for connections that formally had negotiated to have >> them. This new behavior seems to be in line with RFC 7323, section >> 3.2[1]: >> >> "Once TSopt has been successfully negotiated, that is both and >> contain TSopt, the TSopt MUST be sent in every non- >> segment for the duration of the connection, and SHOULD be sent in an >> segment (see Section 5.2 for details)." >> >> As it turns out, macOS does exactly this - send keep-alive packets >> without a timestamp for connections that were negotiated to have them. > > I wonder if I'm running into this with ssh connections to freefall. My > outgoing IPv6 connections pass through an ipfw firewall that uses > dynamic rules. When the dynamic rule gets close to expiration, it > generates keep alive packets that just seem to be ignored by freefall. > Eventually the dynamic rule expires, then sometime later sshd on > freefall sends a keepalive which gets dropped at my end. ipfw sends non-compliant keep alives: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253476 Basically, a node after an ipfw instance seems to be broken from the perspective of the peer. Best regards Michael > >