Comparing the output of
traceroute -n wroclaw-elektryk.pl and
traceroute -n -T -p 80 wroclaw-elektryk.pl I find that the route is varying a lot, which can make debugging a bit tricky. But I also found that five hops before reaching the server, I hit a misconfigured firewall, which is responsible for
ping not working.
whois data for the involved hops, it appears the misconfigured firewall is on the link from the backbone provider to the hosting provider. I think a hosting provider should not be enforcing this kind of filters on their customers, so if you cannot get them to disable it, you may be better off switching hosting provider.
traceroute -n -T -p 21 wroclaw-elektryk.pl and
telnet wroclaw-elektryk.pl 21, I find that the connection to the server works just fine. But the FTP server doesn't send any response code after the TCP connection has been established.
Reasons I have previously seen for a server not sending any response code on a newly established TCP connection include:
- Defective storage media
- Kernel bug
- Severely overloaded server
- Server configured to perform reverse DNS before sending a response, and somehow failing.