Appendix B IP Addresses and Subnetting
VMG1312-B Series User’s Guide
323
The following figure shows t he com pany network after subnett ing. There are now two sub-
net works, A and B.
Figure 183 Subnet t ing Exam ple: After Subnet t ing
I n a 25- bit subnet the host I D has 7 bits, so each sub-network has a m axim um of 2
7
– 2 or 126
possible host s ( a host I D of all zeroes is t he subnet ’s address itself, all ones is t he subnet’s
broadcast address) .
192.168.1.0 with 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 its broadcast address. Therefore, the lowest I P address t hat can be assigned to
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 illust rated using a 25-bit subnet m ask to divide a 24- bit addr ess int o two
subnets. Sim ilarly, t o divide a 24-bit address int o four subnets, you need t o “ borrow” t wo host I D
bit s t o give four possible com binations ( 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 contains 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 itself, all ones is t he subnet ’s broadcast address) .
Table 115 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
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