ZyXEL NBG-416N Guia Do Utilizador

 Appendix A IP Addresses and Subnetting

NBG-416N User’s Guide

You can use subnetting to divide one network into multiple sub-networks. In the 
following example a network administrator creates two sub-networks to isolate a 
group of servers from the rest of the company network for security reasons.

In this example, the company network address is 192.168.1.0. The first three 
octets of the address (192.168.1) are the network number, and the remaining 
octet is the host ID, allowing a maximum of 2

8

 – 2 or 254 possible hosts.

The following figure shows the company network before subnetting. 

Figure 96   Subnetting Example: Before Subnetting

You can “borrow” one of the host ID bits to divide the network 192.168.1.0 into 
two separate sub-networks. The subnet mask is now 25 bits (255.255.255.128 or 
/25).

The “borrowed” host ID bit can have a value of either 0 or 1, allowing two 
subnets; 192.168.1.0 /25 and 192.168.1.128 /25.