Nortel BCM50a, Configuration Manual

Page: 235 / 315

Appendix F IP subnetting 235
BCM50a Integrated Router Configuration — Advanced
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.
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
7
– 2 or 126 hosts for each subnet.
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.
Table 47 Subnet 1
Network number Last Octet bit value
IP Address 192.168.1. 0
IP Address (Binary) 11000000.10101000.00000001. 0 0000000
Subnet Mask 255.255.255. 128
Subnet Mask (Binary) 11111111.11111111.11111111. 1 0000000
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 48 Subnet 2
Network number Last octet bit value
IP Address 192.168.1. 128
IP Address (Binary) 11000000.10101000.00000001. 1 0000000
Subnet Mask 255.255.255. 128
Subnet Mask (Binary) 11111111.11111111.11111111. 1 0000000
Subnet Address: 192.168.1.128 Lowest Host ID: 192.168.1.129
Broadcast Address:
192.168.1.255
Highest Host ID: 192.168.1.254