WatchGuard Technologies SOHO - Manual (Page 20)

How does information travel on the internet?
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How does information travel on the internet?
Each packet of information transported over the Internet must be
packaged in a special way to ensure that it is able to travel from
one computer to the next. A system called Internet Protocol (IP)
takes chunks of information and wraps them up with a header
identifying both where the information is going and how it should
be handled enroute.
IP Addresses
An IP address defines the specific computer on the Internet that
should send or receive a packet. Every computer on the Internet
has a unique address, including your SOHO device. When
defining a service behind your firewall, you need to include the
trusted network address for the machine hosting the application.
On the Internet, IP addresses can be identified using either a string
of numbers or a user-friendly domain name. For example, the IP
address of the WatchGuard site is 209.191.160.60 while the domain
name is www.watchguard.com.
Protocol
A protocol defines how a packet is bundled up and packaged for
shipment across a network. The most commonly used protocols
are Transmission Control Protocol (TCP) and User Datagram
Protocol (UDP). In addition, there are a variety of IP protocols
which are used less frequently.
Port number
The port number alerts the computers at both the sending and
receiving end how to handle the packet.