Date: Wed, 11 Jul 2007 13:14:59 -0500 From: Eric F Crist <ecrist@secure-computing.net> To: Heiko Wundram (Beenic) <wundram@beenic.net> Cc: freebsd-questions@freebsd.org Subject: Re: Some hosting weirdness... Message-ID: <CA922F3A-FFF5-4AC8-9479-77A514D7BEED@secure-computing.net> In-Reply-To: <200707111440.47637.wundram@beenic.net> References: <AF5B51BD-997A-45AE-84C6-41B2D1798632@secure-computing.net> <200707111440.47637.wundram@beenic.net>
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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: >> <snip> >> 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
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