The nerve roots pass through these joints to go from the spinal cord to the arms, legs and other parts of the body. These joints also allow the spine to bend and twist, and they keep the back from slipping too far forward or twisting without limits.
A forward ftp proxy is used to allow internal LAN clients to connect to Internet ftp servers when connecting through a PF firewall. All control and data connection rules are made by the ftp-proxy daemon and inserted into PF using anchors.
FTP is a TCP based service exclusively. There is no UDP component to FTP. FTP is an unusual service in that it utilizes two ports, a 'data' port and a 'command' port (also known as the control port). Traditionally these are port 21 for the command port and port 20 for the data port. The confusion begins however, when we find that depending on the mode, the data port is not always on port 20.