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ZyAIR B-3000 User’s Guide

Appendix H IP Subnetting 200

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.

Table 74 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.

Table 75 Two Subnets Example

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 ... 196 197 198 199 200 201 202 203 204 205 206 ... 220 221

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