Some hosting weirdness...
Eric F Crist
ecrist at secure-computing.net
Wed Jul 11 18:15:04 UTC 2007
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
> 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)
> should send out an ICMP-message with a "Fragmentation needed" error
> appears in the tcpdump), but some don't do that either.
> Generally, the MSS in their SYN-packet when connecting to your
> should be below 1460; most probably at 1452 (which is DSL and cable
> 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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