From owner-freebsd-questions@FreeBSD.ORG Wed Jul 11 18:15:04 2007 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 876AE16A469 for ; Wed, 11 Jul 2007 18:15:04 +0000 (UTC) (envelope-from ecrist@secure-computing.net) Received: from snipe.secure-computing.net (snipe.secure-computing.net [209.240.66.149]) by mx1.freebsd.org (Postfix) with ESMTP id 5824113C44B for ; Wed, 11 Jul 2007 18:15:04 +0000 (UTC) (envelope-from ecrist@secure-computing.net) Received: from [10.0.0.14] (unknown [74.95.66.25]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) (Authenticated sender: ecrist@secure-computing.net) by snipe.secure-computing.net (Postfix) with ESMTP id 1D57217021; Wed, 11 Jul 2007 13:15:02 -0500 (CDT) In-Reply-To: <200707111440.47637.wundram@beenic.net> References: <200707111440.47637.wundram@beenic.net> Mime-Version: 1.0 (Apple Message framework v752.3) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: Content-Transfer-Encoding: 7bit From: Eric F Crist Date: Wed, 11 Jul 2007 13:14:59 -0500 To: Heiko Wundram (Beenic) X-Mailer: Apple Mail (2.752.3) Cc: freebsd-questions@freebsd.org Subject: Re: Some hosting weirdness... X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 11 Jul 2007 18:15:04 -0000 On Jul 11, 2007, at 7:40 AMJul 11, 2007, Heiko Wundram (Beenic) wrote: > On Wednesday 11 July 2007 14:19:09 Eric F Crist wrote: >> >> What should I look for? Is there possibly some weird caching issues >> at their ISPs? How can I fix this? > > Do a tcpdump when someone connects from their network and check for > TCP-MSS > issues, which would be my first guess when small files/items load > fine over > HTTP but items larger than a single TCP-packet won't (which > basically fits > the symptoms you describe). > > As some ISPs will do IP fragmentation when a packet too large to > fit over the > downlink to a customer arrives, you'll not see this problem with > these. Those > ISPs that don't do IP fragmentation on the downlink (quite a few) > generally > should send out an ICMP-message with a "Fragmentation needed" error > (which > appears in the tcpdump), but some don't do that either. > > Generally, the MSS in their SYN-packet when connecting to your > webserver > should be below 1460; most probably at 1452 (which is DSL and cable > AFAIK), > or more generally speaking (their) MTU-40, and the _IP_ packet size > your host > sends back should always be equal to or below the minimum of your > MSS (which > is sent in the SYN/ACK packet) and their MSS, plus 40. If this is > not the > case, you have an issue. Well, I performed a tcpdump as you suggested, and my mss is exactly 1460, not the 1452 you suggest. What does this mean? ----- Eric F Crist Secure Computing Networks