Ticket #10857 (new defect)
Passive FTP connection fails with NAT networking
|Reported by:||jcranmer||Owned by:|
This is something that drove me into a frenzy trying to figure out.
I have a Windows 7 host with a Linux (Debian testing) guest. When trying to run FTP commands via command line ftp (in passive mode), ftplib in Python, and using Firefox's FTP capabilities--all of the above in passive mode--all of them hung when trying to do an FTP LIST command.
After getting so frustrated at why this wasn't working, I finally viewed the log in Wireshark, as seen from within the guest). This is where the bug gets weird: After the PASV command, the server reply got retransmitted exactly once. The next sequence number is indicated to be 1336. The LIST command then gets sent, and the reply is received... except the reply is at 1337, indicating that the guest networking library thinks it's missing a byte. Then it requests retransmission to find that byte, and it keeps receiving the retransmission information starting at 1337.