On Sunday 11 March 2007 14:49, Vic wrote:
> > I've currently got a very strange problem on my firewall. Some
> > people are unable to connect to it, and others can.
>
> Is this across Internet connections? If you're not using commonly-blocked
> ports, I'd be looking straight at MTU...
The clients having problems are outside of my network - at work, and
some random people who have complained about not being able to access
my site.
Both client and server have an MTU of 1500. This is something I've
been assuming, but don't know much about networking at this level,
and haven't been able to find anything obviously wrong.
> > Anybody have any ideas about how to start troubleshooting this?
>
> Install Wireshark on each end & sniff some traffic. That'll pull something
> up.
I'm using tcpdump. If I perform a wget against http from one client, I get:
wget
http://www.glendale.org.uk/index.html
tcpdump: listening on rl1, link-type EN10MB
15:54:41.781669 XX.XX.XX.XX.25204 > 80.176.97.122.80: S 3541765879:3541765879(0) win 512 <mss 1460>
15:54:41.813437 XX.XX.XX.XX.25204 > 80.176.97.122.80: . ack 1623925718 win 7300 (DF)
15:54:41.814391 XX.XX.XX.XX.25204 > 80.176.97.122.80: P 0:117(117) ack 1 win 7300 (DF)
15:54:41.894502 XX.XX.XX.XX.25204 > 80.176.97.122.80: . ack 2921 win 7300 (DF)
15:54:41.933896 XX.XX.XX.XX.25204 > 80.176.97.122.80: . ack 5841 win 7300 (DF)
15:54:41.974549 XX.XX.XX.XX.25204 > 80.176.97.122.80: . ack 9338 win 7300 (DF)
15:54:41.976518 XX.XX.XX.XX.25204 > 80.176.97.122.80: F 117:117(0) ack 9338 win 7300
15:54:42.016693 XX.XX.XX.XX.25204 > 80.176.97.122.80: . ack 9339 win 7300 (DF)
From the same client, against https, I instead get:
wget --no-check-certificate
https://webmail.glendale.org.uk/mail/src/login.php
15:55:04.956658 XX.XX.XX.XX.38688 > 80.176.97.122.443: S 927076470:927076470(0) win 5840 <mss 1460,sackOK,timestamp 89927409 0,nop,wscale 4> (DF)
15:55:04.997284 XX.XX.XX.XX.38688 > 80.176.97.122.443: . ack 229068150 win 365 <nop,nop,timestamp 89927419 791315675> (DF)
15:55:04.998546 XX.XX.XX.XX.38688 > 80.176.97.122.443: P 0:124(124) ack 1 win 365 <nop,nop,timestamp 89927419 791315675> (DF)
At this point the client wget hangs waiting for a reponse.
From another client, the second call works. Both clients are coming from
the same network.
--
Be seeing you, http://www.glendale.org.uk
Sam. Mail/IM (Jabber): sam@???
