Nortel 222 User Manual page 265

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.
Table 60 Subnet 1
IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
Subnet Address: 192.168.1.0
Broadcast Address:
192.168.1.127
Table 61 Subnet 2
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
Note: In the following charts, shaded or bolded last-octet bit values
indicate host ID bits borrowed to form 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.
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
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
Nortel Business Secure Router 222 Configuration — Advanced
Appendix G IP subnetting 265
7 – 2 or 126 hosts for each subnet.
Last Octet bit value
0
00000000
128
10000000
Last octet bit value
128
10000000
128
10000000