ZyXEL B-500 User Guide - Page 193

ZyAIR B-500 Wireless Access Point User's Guide 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 G-4 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. IP Subnetting G-3