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12-22 User’s Reference Guide
FTP sessions. To allow WAN-originated FTP sessions to a LAN-based FTP server with the IP address a.b.c.d
(corresponding to a numbered IP address such as 163.176.8.243), insert the following input filter ahead of the
current input filter 1:
■ Enabled: Yes
■ Forward: Yes
■ Source IP Address: 0.0.0.0
■ Source IP Address Mask: 0.0.0.0
■ Dest. IP Address: a.b.c.d
■ Dest. IP Address Mask: 255.255.255.255
■ Protocol Type: TCP
■ Source Port Comparison: No Compare
■ Source Port ID: 0
■ Dest. Port Comparison: Equal
■ Dest. Port ID: 21
Note: A similar filter could be used to permit Telnet or WWW access. Set the Dest. Port ID to 23 for Telnet or
80 for WWW.
Firewall tutorial
General Firewall Terms
Firewall: a component or set of components that restrict access between a protected network and the Internet,
or between two networks.
Host: A workstation on the Network.
Packet: Unit of communication on the Internet.
Packet Filter: Packet filters allow or deny packets based on source or destination IP addresses, TCP or UDP
ports, or the TCP ACK bit.
Port: A number that defines a particular type of service.
Filter Rule: A filter set is comprised of individual filter rules.
Filter Set: A grouping of individual filter rules.
Basic IP Packet Components
All IP packets contain the same basic “header” information, as follows:
Source IP Address 163.176.132.18
Destination IP Address 163.176.4.27