ZyXEL Communications Dimension ES-2008 User Manual page 157

"borrowing") determines the number of hosts you can have on
IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
Subnet Address: 192.168.1.0
Broadcast Address: 192.168.1.127
IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
Subnet Address: 192.168.1.128
Broadcast Address: 192.168.1.255
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
– 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 give four possible combinations of 00, 01, 10 and 11. The
IP Subnetting
each subnet.
Chart 5 Subnet 1
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
255.255.255.
11111111.11111111.11111111.
Lowest Host ID: 192.168.1.1
Highest Host ID: 192.168.1.126
Chart 6 Subnet 2
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
255.255.255.
11111111.11111111.11111111.
Lowest Host ID: 192.168.1.129
Highest Host ID: 192.168.1.254
Dimension ES-2008 Ethernet Switch
LAST OCTET BIT
0
00000000
128
10000000
LAST OCTET BIT
128
10000000
128
10000000
VALUE
VALUE
7
O