ZyXEL Communications ZYWALL 10W User Manual page 438

ZyWALL 10~100 Series Internet Security Gateway
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 subnet mask is 26 bits
(11111111.11111111.11111111.11000000) or 255.255.255.192. Each subnet contains 6 host ID bits, giving
6
2 -2 or 62 hosts for each subnet (all 0's is the subnet itself, all 1's is the broadcast address on the subnet).
IP Address
IP Address (Binary)
Subnet Mask (Binary)
Subnet Address: 192.168.1.0
Broadcast Address: 192.168.1.63
IP Address
IP Address (Binary)
Subnet Mask (Binary)
Subnet Address: 192.168.1.64
Broadcast Address: 192.168.1.127
IP Address
IP Address (Binary)
Subnet Mask (Binary)
46
Chart J-7 Subnet 1
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
11111111.11111111.11111111.
Lowest Host ID: 192.168.1.1
Highest Host ID: 192.168.1.62
Chart J-8 Subnet 2
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
11111111.11111111.11111111.
Lowest Host ID: 192.168.1.65
Highest Host ID: 192.168.1.126
Chart J-9 Subnet 3
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
11111111.11111111.11111111.
LAST OCTET BIT VALUE
0
00000000
11000000
LAST OCTET BIT VALUE
64
01000000
11000000
LAST OCTET BIT VALUE
128
10000000
11000000
IP Subnetting