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ZyAIR G-1000 Access Point User’s Guide

IP Subnetting G-3

sequence of ones beginning from the left most bit of the mask, followed by a continuous sequence of zeros,

for a total number of 32 bits.

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 mask 255.255.255.128.

The following table shows all possible subnet masks for a class “C” address using both notations.

Chart 9 Alternative Subnet Mask Notation

SUBNET MASK IP ADDRESS SUBNET MASK “1” BITS LAST OCTET BIT VALUE

255.255.255.0 /24 0000 0000

255.255.255.128 /25 1000 0000

255.255.255.192 /26 1100 0000

255.255.255.224 /27 1110 0000

255.255.255.240 /28 1111 0000

255.255.255.248 /29 1111 1000

255.255.255.252 /30 1111 1100

The first mask shown is the class “C” natural mask. Normally if no mask is specified it is understood that

the natural mask is being used.

Example: Two Subnets

As an example, you have a class “C” address 192.168.1.0 with subnet mask of 255.255.255.0.

NETWORK NUMBER HOST ID

IP Address 192.168.1. 0

IP Address (Binary) 11000000.10101000.00000001. 00000000

Subnet Mask 255.255.255. 0

Subnet Mask (Binary) 11111111.11111111.11111111. 00000000

The first three octets of the address make up the network number (class “C”). You want to have two

separate networks.

1 2 ... 170 171 172 173 174 175 176 177 178 179 180 ... 196 197

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