I have a linux server running at an isp, it is on a live ip with no firewall between it and the internet, then at home I have dsl, my linux machine at home has the live ip of the dsl, I can ftp from my linux machine at home to my linux server at the isp and it works fine but if I try to connect from my laptop, (winxp) to the server it doesn't work, the linux server is doing ip masqerading for the laptop so my laptop has a 10.0.0.10 address. I will post what I get at a command line below, I am changing the server info for securitys sake.
Also as a sidenote, I can ftp to the server with this same laptop when I am on a live ip and not behind my linux firewall.
C:\Documents and Settings\marcus>ftp host.somewhere.net
Connected to host.somewhere.net.
220-=(<*>)=-.:. (( Welcome to PureFTPd 1.0.12 )) .:.-=(<*>)=-
220-You are user number 1 of 50 allowed.
220-Local time is now 22:12 and the load is 0.00. Server port: 21.
220-This is a private system - No anonymous login
220 You will be disconnected after 15 minutes of inactivity.
331 User marcus OK. Password required
230-User marcus has group access to: krazyqui root
230 OK. Current restricted directory is /
500 I won't open a connection to 10.0.0.10 (only to 188.8.131.52)
425 No data connection