ZyXEL Communications Corporation MAX207HW2 Manuel D’Utilisation

Appendix D IP Addresses and Subnetting

User’s Guide

Since the mask is always a continuous number of ones beginning from the left, 
followed by a continuous number of zeros for the remainder of the 32 bit mask, 
you can simply specify the number of ones instead of writing the value of each 
octet. This is usually specified by writing a “/” followed by the number of bits in 
the mask after the address. 

For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with subnet mask 
255.255.255.128. 

The following table shows some possible subnet masks using both notations. 

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.

Table 74   Alternative Subnet Mask Notation

255.255.255.0

/24

0000 0000

0

255.255.255.128

/25

1000 0000

128

255.255.255.192

/26

1100 0000

192

255.255.255.224

/27

1110 0000

224

255.255.255.240

/28

1111 0000

240

255.255.255.248

/29

1111 1000

248

255.255.255.252

/30

1111 1100

252