Reference Manual for the ProSafe VPN Firewall FVS318v3
Network, Routing, and Firewall Basics B-3
January 2005
The latter version is easier to remember and easier to enter into your computer.
In addition, the 32 bits of the address are subdivided into two parts. The first part of the address
identifies the network, and the second part identifies the host node or station on the network. The
dividing point may vary depending on the address range and the application.
There are five standard classes of IP addresses. These address classes have different ways of
determining the network and host sections of the address, allowing for different numbers of hosts
on a network. Each address type begins with a unique bit pattern, which is used by the TCP/IP
software to identify the address class. After the address class has been determined, the software
can correctly identify the host section of the address. The follow figure shows the three main
address classes, including network and host sections of the address for each address type.
Figure B-1: Three Main Address Classes
The five address classes are:
• Class A
Class A addresses can have up to 16,777,214 hosts on a single network. They use an eight-bit
network number and a 24-bit node number. Class A addresses are in this range:
1.x.x.x to 126.x.x.x.
• Class B
Class B addresses can have up to 65,354 hosts on a network. A Class B address uses a 16-bit
network number and a 16-bit node number. Class B addresses are in this range:
128.1.x.x to 191.254.x.x.
lass A
etwork Node
lass B
lass C
Network Node
Network Node
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