Red Hat ENTERPRISE LINUX AS 2.1 -, Installation Manual

Page: 129 / 210

Section 8.4:FTP In an LVS Cluster 129
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 Section 8.5, Saving Network Packet
Filter Settings
8.4 FTP In an LVS Cluster
File Transport Protocol (FTP) is an old and complex multi-port protocol that presents a distinct set of
challenges to a clustered environment. To understand the nature of these challenges, you must first
understand some key things about how FTP works.
8.4.1 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 an 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 seperate data connection. Most modern FTP clients attempt to establish a
passive connection to FTP
The two important things to note about all of this in regards to clustering is:
1. The client determines the type of connection, not the server. This means, to effectively cluster
FTP, you must configure the LVS routers to handle both active and passive connections.