Some hosting weirdness...
Heiko Wundram (Beenic)
wundram at beenic.net
Wed Jul 11 13:08:57 UTC 2007
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.
--
Heiko Wundram
Product & Application Development
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Beenic Networks GmbH
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Mail wundram at beenic.net
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