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Appendix D IP Addresses and Subnetting

ZyXEL NWA-3160 Series User’s Guide

286

Subnetting

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

– 2 or 254 possible hosts.

The following figure shows the company network before subnetting.

Figure 191 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.

The following figure shows the company network after subnetting. There are now two sub-

networks, A and B.

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

Table 108 Alternative Subnet Mask Notation (continued)

SUBNET MASK

ALTERNATIVE

NOTATION

LAST OCTET

(BINARY)

LAST OCTET

(DECIMAL)

1 2 ... 281 282 283 284 285 286 287 288 289 290 291 ... 313 314

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Zyxel-communications NWA3160 Manual do Utilizador Página 286