From owner-freebsd-stable Thu Oct 25 18:36:18 2001 Delivered-To: freebsd-stable@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [216.240.41.2]) by hub.freebsd.org (Postfix) with ESMTP id 5CCE737B401 for ; Thu, 25 Oct 2001 18:36:15 -0700 (PDT) Received: (from dillon@localhost) by apollo.backplane.com (8.11.6/8.9.1) id f9Q1a8917003; Thu, 25 Oct 2001 18:36:08 -0700 (PDT) (envelope-from dillon) Date: Thu, 25 Oct 2001 18:36:08 -0700 (PDT) From: Matthew Dillon Message-Id: <200110260136.f9Q1a8917003@apollo.backplane.com> To: David Raistrick Cc: john_wilson100@excite.com, freebsd-stable@FreeBSD.ORG Subject: Re: 4.4-STABLE machine unusable (was Re: Openssh) References: Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG :On Thu, 25 Oct 2001 john_wilson100@excite.com wrote: : :> Guys, :> :> You can say all you like, but something in stable is totally fscked up. As :> soon as I log in and start doing anything that involves a bit of traffic :> (e.g. tailing a file), the connection freezes and I have to kill it. sshd :> doesn't die, so I can log in again. I can reproducibly freeze it by :> doing... well practically anything: :> :> tail /var/log/messages, vi, cat, etc. all freeze the connection. Strangely :> enough, : :I've seen this before, or something that sounds identical. telnet did the :same thing, and anything over a size i dont remember via http did it as :well. : :The workaround I found was to drop the MTU on the ethernet card (a generic :ne2k card at the time, no idea what it was plugged into.) down to 512 and :it was fine. Move it above 512 and the problems came back. :... TCP does what is known as MTU discovery to figure out the lowest MTU in the connection path. TCP then sets the no-frag bit on its packets. This can break down if you are running through a misconfigured firewall or an intermediate router or machine does not respond with the correct ICMP error when an oversized no-frag packet is received. If the firewall blocks ICMP error #3 (destination unreachable) subcode 4, your TCP connection will not properly detect the MTU. Reducing the client machine's interface MTU is a work-around (it sets a maximum MTU which is hopefully less then the maximum MTU of routers in between you and the destination), but the best solution is to figure out where the misconfigured router/machine is and fix it. -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message