Administrator’s Handbook
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:
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 |
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.
