Dividing a big network into many smaller networks is called subnetting.

advantages:

privacy.

Example:

we have 200.0.0.0 network address
by seeing first octet we can tell it’s class c,and have 256 hosts,for small network it’s huge right let’s divide the network into 2 subnets.

if we choose one bit from binary we have divided the bits into parts

0
1

if we choose 2 bits entire bit space divided into 4 parts.

00
01
10
11

like wise 3 bits 8 parts (2^3=8)
.

To divide network into 2 parts we need one bit ,so borrow one bit from host id

part1	part2
00000000	1000000

range

subnet1	subnet2
00000000	10000000
01111111	11111111
0-127	128-255

now we have 2 subnets one subnet contains 0-127,other 128-255

what is networkid and what is broadcat id if we do subnetting?

if u are inside network u know u done subnetting and u tell nid ,bid of subnets only
if u are outside the network nid,bid used as usual frist and last ip.

subnet mask

32 bit number
series of 1’s represents nid&sid
series of 0’s represents host id

subnet mask for the class c network is 255.255.255.0
subnet mask of classc network in binary binary 11111111.11111111.11111111.00000000
now we borrow 1 bit from host id so our new subnet mask contain 11111111.11111111.11111111.10000000 i.e 255.255.255.128
by using incomming packet router has to identify network to which ip address belongs to
router will take incoming ip and do bitwise and with subnet mask to get nid to which ip belongs to in routing taable.

Routing table

nid	subnet mask	interface
200.0.0.0	255.255.255.128	a
200.0.0.128	255.255.255.128	b
0.0.0.0	0.0.0.0	c