User guide

Check Point Stateful Inspection Technology
16 Check Point ZoneAlarm User Guide
Step Channel
Type
Description Source TCP
Source
Port
Destination TCP
Destination
Port
2 CMD Server responds
with data port
information P >
1023
FTP
server
21 FTP client C
3 Data Client initiates data
connection to
server on port P
FTP
client
D >
1023
FTP server P
4 Data Server
acknowledges
data connection
FTP
server
P FTP client D
The following diagram demonstrates the establishment of a Passive FTP connection
through a firewall protecting the FTP server.
From the FTP server's perspective, the following connections are established:
• Command connection from the client on a port greater than 1023, to the server
on port 21
• Data connection from the client on a port greater than 1023, to the server on a
port greater than 1023
Figure 3: Establishment of Passive FTP Connection