ZyXEL p-660hwp Guia Do Utilizador

P-660HWP-Dx User’s Guide

This appendix introduces addresses, IP address classes and subnet masks.

An IP address is made up of four octets, written in dotted decimal notation (for example, 
192.168.1.1). An octet is an 8-digit binary number. Therefore, each octet has a possible range 
of 00000000 to 11111111 in binary, or 0 to 256 in decimal.
An IP address has two parts: the network number and the host ID. Routers use the network 
number to send packets to the correct network, while the host ID identifies a single device on 
the network.

The class of an IP address determines the number of hosts you can have on your network.

• In a class A address the first octet is the network number, and the remaining three octets 

are the host ID. 

• In a class B address the first two octets make up the network number, and the two 

remaining octets make up the host ID.

• In a class C address the first three octets make up the network number, and the last octet is 

the host ID.

The following table shows the network number and host ID arrangement for classes A, B and 
C.

An IP address with host IDs of all zeros is the IP address of the network.  An IP address with 
host IDs of all ones is the broadcast address for that network. Therefore, to determine the total 
number of hosts allowed in a network, deduct two as shown next:

• A class C address (1 host octet:

 

8 host bits) can have 2

8

 – 2, or 254 hosts. 

• A class B address (2 host octets: 16 host bits) can have 2

16

 – 2, or 65534 hosts. 

A class A address (3 host octets: 24 host bits) can have 2

24

 – 2 hosts, or approximately 16 

million hosts. 

Table 154   Classes of IP Addresses

Class A

Network number Host ID

Host ID

Host ID

Class B

Host ID

Host ID

Class C

Host ID