ZyXEL G-405 User Guide - Page 88

Example: Four Subnets, Chart 8-5 Subnet 1

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ZyAIR G-405 User's Guide 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 8-5 Subnet 1 NETWORK NUMBER LAST OCTET BIT VALUE IP Address 192.168.1. 0 IP Address (Binary) 11000000.10101000.00000001. 00000000 Subnet Mask 255.255.255. 128 Subnet Mask (Binary) 11111111.11111111.11111111. 10000000 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 8-6 Subnet 2 NETWORK NUMBER LAST OCTET BIT VALUE IP Address 192.168.1. 128 IP Address (Binary) 11000000.10101000.00000001. 10000000 Subnet Mask 255.255.255. 128 Subnet Mask (Binary) 11111111.11111111.11111111. 10000000 Subnet Address: 192.168.1.128 Lowest Host ID: 192.168.1.129 Broadcast Address: 192.168.1.255 Highest Host ID: 192.168.1.254 The remaining 7 bits determine the number of hosts each subnet can have. Host IDs of all zeros represent the subnet itself and host IDs of all ones are the broadcast address for that subnet, so the actual number of hosts available on each subnet in the example above is 27 - 2 or 126 hosts for each subnet. 192.168.1.0 with mask 255.255.255.128 is the subnet itself, and 192.168.1.127 with mask 255.255.255.128 is the directed broadcast address for the first subnet. Therefore, the lowest IP address that can be assigned to an actual host for the first subnet is 192.168.1.1 and the highest is 192.168.1.126. Similarly the host ID range for the second subnet is 192.168.1.129 to 192.168.1.254. Example: Four Subnets The above example illustrated using a 25-bit subnet mask to divide a class "C" address space into two subnets. Similarly to divide a class "C" address into four subnets, you need to "borrow" two host ID bits to N IP Subnetting

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ZyAIR G-405 User’s Guide
N
IP Subnetting
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 8-5 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 8-6 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
Subnet Mask (Binary)
11111111.11111111.11111111.
1
0000000
Subnet Address: 192.168.1.128
Lowest Host ID: 192.168.1.129
Broadcast Address: 192.168.1.255
Highest Host ID: 192.168.1.254
The remaining 7 bits determine the number of hosts each subnet can have. Host IDs of all zeros represent
the subnet itself and host IDs of all ones are the broadcast address for that subnet, so the actual number of
hosts available on each subnet in the example above is 2
7
– 2 or 126 hosts for each subnet.
192.168.1.0 with mask 255.255.255.128 is the subnet itself, and 192.168.1.127 with mask 255.255.255.128
is the directed broadcast address for the first subnet. Therefore, the lowest IP address that can be assigned
to an actual host for the first subnet is 192.168.1.1 and the highest is 192.168.1.126. Similarly the host ID
range for the second subnet is 192.168.1.129 to 192.168.1.254.
Example: Four Subnets
The above example illustrated using a 25-bit subnet mask to divide a class “C” address space into two
subnets. Similarly to divide a class “C” address into four subnets, you need to “borrow” two host ID bits to