ZyXEL Communications P-660R-D Series - Manual (Page 180)

P-660R-D Series User’s Guide
4 Appendix E IP Addresses and Subnetting
Example: Two Subnets
As an example, you have a class “C” address 192.168.1.0 with subnet mask of 255.255.255.0.
The first three octets of the address make up the network number (class “C”).
To make two networks, divide the network 192.168.1.0 into two separate subnets by converting one of the
host ID bits of the IP address to a network number bit. The “borrowed” host ID bit can be either “0” or “1”
thus giving two subnets; 192.168.1.0 with mask 255.255.255.128 and 192.168.1.128 with mask
255.255.255.128.
Note: In the following charts, shaded/bolded last octet bit values indicate host ID bits “borrowed”
to make 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.
Table 69 Two Subnets Example
IP/SUBNET MASK NETWORK NUMBER HOST ID
IP Address 192.168.1. 0
IP Address (Binary) 11000000.10101000.00000001. 00000000
Subnet Mask 255.255.255. 0
Subnet Mask (Binary) 11111111.11111111.11111111. 00000000
Table 70 Subnet 1
IP/SUBNET MASK 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
Table 71 Subnet 2
IP/SUBNET MASK 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