I've been pulling my hair out with a proftp problem for a few months now and I'm at a loss as to why it doesn't work.
Almost everyone globally have no problem connecting to Ftp in passive and active modes but a group of people within a particular external network only get as far as the inital login stages - or slightly further before their connection hangs and times out. But they have no problem with ftp connections to other sites.
I've read somewhere that this has to do with port 113 authentication. The administrator of the affected network has told me that he is seeing port 113 traffic to my server and this is being filtered out on their firewall which explains why the connection timing out.
The server is in standalone mode on a Cobalt Raq3 machine. I've set IdentLookups off as well as ReverseDNS lookups off. I would have expected this to sort out the problem but it's still failing. Is there something I'm forgetting to disable? Could xinetd/inetd be opening connections on port 113?