P-2812HNU-51c User’s Guide
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CHAPTER 13
Firewall
13.1 Overview
This chapter shows you how to enable and configure the P-2812HNU-51c firewall
settings.
The P-2812HNU-51c firewall is a packet filtering firewall and restricts access based
on the source/destination computer network address of a packet and the type of
application.
13.1.1 What You Can Do in this Chapter
The Incoming screen lets you view and configure incoming IP filtering rules
(Section 13.3 on page 276).
13.2 What You Need to Know
The following terms and concepts may help as you read through this chapter.
Basics
Computers share information over the Internet using a common language called
TCP/IP. TCP/IP, in turn, is a set of application protocols that perform specific
functions. An “extension number”, called the "TCP port" or "UDP port" identifies
these protocols, such as HTTP (Web), FTP (File Transfer Protocol), POP3 (E-mail),
etc. For example, Web traffic by default uses TCP port 80.
When computers communicate on the Internet, they are using the client/server
model, where the server "listens" on a specific TCP/UDP port for information
requests from remote client computers on the network. For example, a Web
server typically listens on port 80. Please note that while a computer may be
intended for use over a single port, such as Web on port 80, other ports are also
active. If the person configuring or managing the computer is not careful, a hacker
could attack it over an unprotected port.
