ZyXEL Communications Corporation P660HNT1H Benutzerhandbuch

Appendix B IP Addresses and Subnetting

P-660HN-T1h User’s Guide

The following figure shows an example IP address in which the first three octets 
(192.168.1) are the network number, and the fourth octet (16) is the host ID.

Figure 147   Network Number and Host ID

How much of the IP address is the network number and how much is the host ID 
varies according to the subnet mask.  

A subnet mask is used to determine which bits are part of the network number, 
and which bits are part of the host ID (using a logical AND operation). The term 
“subnet” is short for “sub-network”.

A subnet mask has 32 bits. If a bit in the subnet mask is a “1” then the 
corresponding bit in the IP address is part of the network number. If a bit in the 
subnet mask is “0” then the corresponding bit in the IP address is part of the host 
ID. 

The following example shows a subnet mask identifying the network number (in 
bold text) and host ID of an IP address (192.168.1.2 in decimal).

Table 99   Subnet Masks

IP Address (Binary)

11000000

10101000

00000001

00000010

Subnet Mask (Binary)

11111111 11111111 11111111 00000000

Network Number

Host ID

00000010