User's Manual

Appendix A IP Addresses and Subnetting
B222s User’s Guide
183
The following figure shows t he com pany network aft er subnetting. There are now t wo sub-
networ ks, A and B.
Figure 103 Subnet ting Exam ple: After Subnet t ing
I n a 25- bit subnet t he host I D has 7 bit s, so each sub- net work has a m axim um of 2
7
– 2 or 126
possible host s (a host I D of all zeroes is the subnet ’s address it self, all ones is t he subnet ’s
broadcast address) .
192.168.1.0 wit h m ask 255.255.255.128 is subnet A it self, and 192.168.1.127 wit h m ask
255.255.255.128 is it s broadcast address. Therefore, the lowest I P address that can be assigned t o
an act ual host for subnet A is 192.168.1.1 and t he highest is 192.168.1.126.
Sim ilarly, t he host I D range for subnet B is 192.168.1.129 t o 192.168.1.254.
Example: Four Subnets
The previous exam ple illustrat ed using a 25- bit subnet m ask to divide a 24- bit address int o two
subnet s. Sim ilarly, t o divide a 24- bit address int o four subnet s, you need t o “ bor row” t wo host I D
bits t o give four possible com binat ions ( 00, 01, 10 and 11) . The subnet m ask is 26 bit s
( 11111111.11111111.11111111.1 1 000000) or 255.255.255.192.
Each subnet cont ains 6 host I D bits, giving 2
6
- 2 or 62 hosts for each subnet ( a host I D of all
zeroes is t he subnet it self, all ones is t he subnet ’s broadcast address) .
Table 78 Subnet 1
IP/SUBNET MASK NETWORK NUMBER
LAST OCTET BIT
VALUE
I P Address ( Decim al) 192.168.1. 0
I P Address ( Binary) 11000000.10101000.00000001. 0 0 000000
Subnet Mask ( Binary) 11111111.11111111.11111111. 1 1 000000