ZyXEL p-334wh Guia Do Utilizador

P-334WH User’s Guide

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Appendix D IP Addresses and Subnetting

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

Table 89   Classes of IP Addresses 

Class A

Network number Host ID

Host ID

Host ID

Class B

Host ID

Host ID

Class C

Host ID

An IP address with host IDs of all zeros is the IP address of the network (192.168.1.0 for 
example). An IP address with host IDs of all ones is the broadcast address for that network  
(192.168.1.255 for example). 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. 

The value of the first octet of an IP address determines the class of an address. 

• Class A addresses have a 0 in the leftmost bit. 
• Class B addresses have a 1 in the leftmost bit and a 0 in the next leftmost bit. 
• Class C addresses start with 1 1 0 in the first three leftmost bits. 
• Class D addresses begin with 1 1 1 0. Class D addresses are used for multicasting, which 

is used to send information to groups of computers.

• There is also a class E. It is reserved for future use.

The following table shows the allowed ranges for the first octet of each class. This range 
determines the number of subnets you can have in a network.

Table 90   Allowed IP Address Range By Class 

Class A

00000000 to 01111111

0 to 127

Class B

10000000 to 10111111

128 to 191

Class C

11000000 to 11011111

192 to 223

Class D

11100000 to 11101111

224 to 239

Class E
(reserved)

11110000 to 11111111

240 to 255