Specifications

Administrator’s Handbook
158
Firewall Tutorial
General firewall terms
☛ Note:
Breakwater Basic Firewall (see “BreakWater Basic Firewall” on page 142) does not make
use of the packet filter support and can be used in addition to filtersets
Filter rule: A filter set is comprised of individual filter rules.
Filter set: A grouping of individual filter rules.
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.
Port: A number that defines a particular type of service.
Basic IP packet components
All IP packets contain the same basic header information, as follows:
This header information is what the packet filter uses to make filtering decisions. It is important to note
that a packet filter does not look into the IP data stream (the User Data from above) to make filtering deci-
sions.
Basic protocol types
TCP: Transmission Control Protocol. TCP provides reliable packet delivery and has a retransmission mech-
anism (so packets are not lost). RFC 793 is the specification for TCP.
Source IP Address 163.176.132.18
Destination IP Address 163.176.4.27
Source Port 2541
Destination Port 80
Protocol TCP
DATA User Data