Motorola Netopia 3342N - Manual (Page 158)

Administrator’s Handbook
158
Firewall Tutorial
General firewall terms
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Note:
Breakwater Basic Firewall (see “BreakWater Basic Firewall” on page 142 ) does not make
use of the packet filter suppor t 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
por ts.
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 impor tant 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 Por t 2541
Destination Por t 80
Protocol TCP
DATA User Data