I have a small LAN at home connected up to the net via a DSL modem on a
gateway machine running lenny and iptables.
I have a problem with some software running on a windows machine on the
LAN where the company who wrote the sofware say that there must be
something wrong with my internet connection, but can't help any further.
I'd like to know what tests I can run to verify that my config and my
firewall are OK, especially regarding PMTU.
I had an issue before this which I solved by adding some ICMP related
rules to iptables, and by disabling the firewall on my DSL modem, which
is undocumented by the manufacturer (and denied by their Support). It's
iptables running on an embedded linux and resets itself every power
cycle. I think it does ICMP clamping but I can telnet onto the modem and
drop the rules (as long as I remember).
What can I do with ping? This ping command gives suspicious results:
ping -s 1473 mktgw1.ibllc.com
One byte less and it works. Fragmentation also works for normal websites
like news.bbc.co.uk.
I'd massively appreciate any help with this! I'm stuck with either my
own mistake, or until I can prove I haven't made one.