Sounds like exactly what you're seeing, I know our watchguard firebox proxies FTP connections so it looks like every box has FTP installed even if they don't.
Few days ago I had another server on the same IP (it's IP for tests before production place), which was FTP server. So maybe that's a reason?
I have new server on CentOS 4.1 - fresh installation. During security tests I've noticed:
When I scan server ports (nmap) from the outside there is 21 tcp port open. But when I check on the server (netstat -tan or lsof -i) there is no any open 21 tcp port.
Any ideas? To be honest I'm confused.
Regards
P.S.: of course I don't have started FTP service. Even I don't have installed FTP server.
Do you have a router/firewall in front of your server? If you are using something like http://www.grc.com to scan from the Internet you are probably getting a response from the router/firewall in front of your server not from the server itself.