ZyXEL Communications Prestige 662HW Series, User Manual

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Prestige 662HW Series User’s Guide
IP Subnetting B-3
Chart B-4 Alternative Subnet Mask Notation
SUBNET MASK IP ADDRESS SUBNET MASK “1” BITS LAST OCTET BIT VALUE
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.
Divide the network 192.168.1.0 into two separate subnets by converting one of the host ID bits of the
IP address to a network number bit. The “borrowed” host ID bit can be either “0” or “1” thus giving
two subnets; 192.168.1.0 with mask 255.255.255.128 and 192.168.1.128 with mask 255.255.255.128.
In the following charts, shaded/bolded last octet bit values indicate host ID bits “borrowed” to form
network ID bits. The number of “borrowed” host ID bits determines the number of subnets you can
have. The remaining number of host ID bits (after “borrowing”) determines the number of hosts you
can have on each subnet.
Chart B-5 Subnet 1
NETWORK NUMBER LAST OCTET BIT VALUE
IP Address 192.168.1. 0
IP Address (Binary) 11000000.10101000.00000001. 0 0000000
Subnet Mask 255.255.255. 128
Subnet Mask (Binary) 11111111.11111111.11111111. 1 0000000
Subnet Address: 192.168.1.0 Lowest Host ID: 192.168.1.1
Broadcast Address: 192.168.1.127 Highest Host ID: 192.168.1.126
Chart B-6 Subnet 2
NETWORK NUMBER LAST OCTET BIT VALUE
IP Address 192.168.1. 128
IP Address (Binary) 11000000.10101000.00000001. 1 0000000
Subnet Mask 255.255.255. 128