ZyXEL Communications P-660HN-51 - Page 267

Appendix B IP Addresses and Subnetting
P-660HN-51 User’s Guide
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Figure 173 Subnetting Example: After Subnetting
In a 25-bit subnet the host ID has 7 bits, so each sub-network has a maximum of 2
7
– 2 or 126 possible
hosts (a host ID of all zeroes is the subnet’s address itself, all ones is the subnet’s broadcast address).
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 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).
Table 108 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