Configuring Ftp; How Ftp Works - Red Hat LINUX VIRTUAL SERVER 5.0 - ADMINISTRATION Manual

Chapter 3. Setting Up LVS
HTTP and HTTPS virtual servers. These commands have the net effect of assigning any traffic
addressed to the VIP on the appropriate ports a firewall mark of 80, which in turn is recognized
by IPVS and forwarded appropriately.
Warning
The commands above will take effect immediately, but do not persist through a
reboot of the system. To ensure network packet filter settings are restored upon
reboot, refer to

5. Configuring FTP

File Transport Protocol (FTP) is an old and complex multi-port protocol that presents a distinct
set of challenges to an LVS environment. To understand the nature of these challenges, you
must first understand some key things about how FTP works.

5.1. How FTP Works

With most other server client relationships, the client machine opens up a connection to the
server on a particular port and the server then responds to the client on that port. When an FTP
client connects to an FTP server it opens a connection to the FTP control port 21. Then the
client tells the FTP server whether to establish an active or passive connection. The type of
connection chosen by the client determines how the server responds and on what ports
transactions will occur.
The two types of data connections are:
Active Connections
When an active connection is established, the server opens a data connection to the client
from port 20 to a high range port on the client machine. All data from the server is then
passed over this connection.
Passive Connections
When a passive connection is established, the client asks the FTP server to establish a
passive connection port, which can be on any port higher than 10,000. The server then
binds to this high-numbered port for this particular session and relays that port number back
to the client. The client then opens the newly bound port for the data connection. Each data
request the client makes results in a separate data connection. Most modern FTP clients
attempt to establish a passive connection when requesting data from servers.
Note
The client determines the type of connection, not the server. This means to
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Section 6, "Saving Network Packet Filter Settings"