FTP = HTTP GET ftp://...

Today I was in for a surprise: at a customer I was investigating how to reach an FTP server outside their firewall. From within my browser I could easily reach the FTP server with the URL
ftp://user:password@ftp.company.com, thereby going through the FTP/HTTP proxy.

But when I tried to do the same with FileZilla, the free FTP client, I couldn't access the FTP server. Ultimately I did some sniffing using WireShark. And to my surprise, the browser was talking HTTP tot the proxy, no FTP on the wire! I noticed the HTTP request "HTTP GET ftp://..." being sent to the proxy. And FTP listings coming back, formatted as HTML!

So learned a new thing: "FTP over HTTP" !