Subnetting In Practice

Imagine that you need to make four different networks(LAN’s). Then you ask form ISP(Internet Service Provider) to four different IP’s. But each of network has less than 20 computers. So ISP will say we cannot give four IP’s and we give you one IP and Split it into four difference networks. Let see how we done it.

ISP given network address: 192.168.5.0 255.255.255.0                                                                                                                                 

The number of networks that we have : 4 (2^2)

192.168.5.00000000        (we take two bits from available host’s bits because we need four different networks).

   

  0     0    0   0   0  0  0   0        (consider last 8 bits)

128  64  32 16  8  4  2   1

00  -> 192.168.5.0       LAN A                               

01 -> 192.168.5.64      LAN B

10 ->192.168.5.128     LAN C

11->192.168.5.192      LAN D

LAN Name	Network Address	Broadcast Address	Host’s IP Range
LAN A	192.168.5.0/26	192.168.5.63	192.168.5.1 to 62
LAN B	192.168.5.64/26	192.168.5.127	192.168.5.65 to 126
LAN C	192.168.5.128/26	192.168.5.191	192.168.5.129 to 190
LAN D	192.168.5.192/26	192.168.5.255	192.168.5.193 to 254

 Each network(LAN) should have network address and broadcast address.
let we discuss how we find network and broadcast address.I take LAN B for this work.
LAN B network address : 192.168.5.64/26    final 8 bits->  01000000  
01 (left very first two bits) goes to network side and remaining 6 bits are only available for hosts.

When we give all that 6 bits to 0(zero) that number gives network address of LAN B -> 192.168.5.01000000



When we give all that 6 bits to 1(one's) that number gives broadcast address of LAN B -> 192.168.5.01111111


    0         1    1    1   1  1  1  1
128*0 +64+32+16+8+4+2+1 = 127
That is the way we define network and broadcast address.