ZyXEL VFG6005 User Guide - Page 111

Example: Four Subnets

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192.168.1.0 with mask 255.255.255.128 is subnet A itself, and 192.168.1.127 with mask 255.255.255.128 is its broadcast address. Therefore, the lowest IP address that can be assigned to an actual host for subnet A is 192.168.1.1 and the highest is 192.168.1.126. Similarly, the host ID range for subnet B is 192.168.1.129 to 192.168.1.254. Example: Four Subnets The previous example illustrated using a 25-bit subnet mask to divide a 24-bit address into two subnets. Similarly, to divide a 24-bit address into four subnets, you need to ―borrow‖ two host ID bits to give four possible combinations (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 26 - 2 or 62 hosts for each subnet (a host ID of all zeroes is the subnet itself, all ones is the subnet's broadcast address). Subnet 1 IP/SUBNET MASK NETWORK NUMBER LAST OCTET BIT VALUE IP Address (Decimal) 192.168.1. 0 IP Address (Binary) 11000000.10101000.00000001. 00000000 Subnet Mask (Binary) 11111111.11111111.11111111. 11000000 Subnet Address: 192.168.1.0 Lowest Host ID: 192.168.1.1 Broadcast Address: 192.168.1.63 Highest Host ID: 192.168.1.62 102

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102
192.168.1.0 with mask 255.255.255.128 is subnet
A
itself, and 192.168.1.127 with mask 255.255.255.128 is its broadcast
address. Therefore, the lowest IP address that can be assigned to an actual host for subnet
A
is 192.168.1.1 and the
highest is 192.168.1.126.
Similarly, the host ID range for subnet
B
is 192.168.1.129 to 192.168.1.254.
Example: Four Subnets
The previous example illustrated using a 25-bit subnet mask to divide a 24-bit address into two subnets. Similarly, to divide
a 24-bit address into four subnets, you nee
d to ―borrow‖ two host ID bits to give four possible combinations (00, 01, 10 and
11). The subnet mask is 26 bits (11111111.11111111.11111111.
11
000000) or 255.255.255.192.
Each subnet contains 6 host ID bits, giving 2
6
- 2 or 62 hosts for each subnet (a host ID of all zeroes is the subnet itself, all
ones is the subnet‘s broadcast address).
Subnet 1
IP/SUBNET MASK
NETWORK NUMBER
LAST OCTET BIT
VALUE
IP Address (Decimal)
192.168.1.
0
IP Address (Binary)
11000000.10101000.00000001.
00
000000
Subnet Mask (Binary)
11111111.11111111.11111111.
11
000000
Subnet Address:
192.168.1.0
Lowest Host ID: 192.168.1.1
Broadcast Address:
192.168.1.63
Highest Host ID: 192.168.1.62