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IBIBLIO is dead (Miscellaneous)

posted by mbbrutman(R) Homepage, Washington, USA, 22.05.2015, 06:49

The issue is that in 1987 FTP servers and clients never sat behind firewalls, so they were free to both receive incoming connections (the control connection) and make outgoing connections (PORT mode for data connections).

First, home firewalls screwed up PORT connections by blocking them - they look like random incoming connections from the outside world, which is generally not expected. PASSIVE mode was the response to this; if the client wanted a data connection it would be responsible for making it. The reasoning was that if the client was able to make the control connection, then it would be able to use PASSIVE mode to make the data connection the same way. (PASSIVE is from the view of the server; instead of the server dialing out to the client to send data, the client dials the server while the server passively stands by.)

Later firewalls started snooping on FTP control session packets and fixed PORT mode to make it work. They detect PORT mode connections and allow those through based on the contents of your control connection. Unless of course you use a non-standard FTP control connection port... then all bets are off.

The problem with ibiblio is that their server is behind a firewall. So while the firewall directly routes incoming connections, it doesn't know to fix the PASV command responses from the server to advertise the publicly available IP address, not the internal network IP address. I had this problem with the mTCP FTP server and I provide a simple "advertise this as your IP address" setting to get around it. The good folks at ibiblio either have to fix the firewall to rewrite those responses or do a configuration change to the FTP server to get it to advertise the correct address for PASV connections.

In reality nobody ever made use of third machines for data transfers. It can safely be assumed to be an error.

mTCP - TCP/IP apps for vintage DOS machines!


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