1. TODAY’S AGENDA
SUB NETTING

2. 



WAQAS YOUSAF
ZAEEM HASSAN
WAQAS AKRAM
IRFAN MUNAIR
10-TE-12
10-TE-98
10-TE-64
10-TE-22

3. 
In sub netting, a network is divided into
smaller sub networks with each subnet having
its own subnet address

4. 
Dividing the barrel of apples into small barrels
or baskets does not give us any more apples…
33
33
33

5. 97 Apples
(99– 2)
Before sub netting:
In any network (or subnet) we can
not use all the IP addresses for
host addresses.
We lose two addresses for every
network or subnet.
1. Network Address - One address is
reserved to that of the network.
2. Broadcast Address – One address
is reserved to address all hosts in
that network or subnet.

6. Two parts of IP address
1. Net ID
2. Host ID
 To reach a host, we must first reach the
network using net id, then using host id to
reach the host.


7. 
The 5 IP classes are split up based on the value
in the 1st octet:

8. Sometimes two level hierarchy is not enough.
For example:
An organization with a class B address. The
organization has two levels hierarchical
addressing, but it cannot have more than one
physical network.

•
•
The host cannot be grouped, and all of the
host has the same level
Solution  sub netting

11. • In the above example,
 The rest of the internet is not aware that the network
is divided into three physical subnet.
 A packet destined for host 141.14.2.21 still reaches
router R1. The destination address of the IP datagram
is still a class B where
• 141.14 defines the net id
• And 2.21 defines the host
 However, when the datagram arrives a router
R1, the interpretation of the IP address changes.
• R1 knows the network 141.14 physically divided into three
subnets.
• It knows that the last two octets define two things: subnet id
and host id ( 2.21  subnet id 2 and host id 21)
• Router uses first two octets as net id, the third subnet id, and
the fourth host id

13. 
A class A address:



Is made of a one-byte net id and a three-byte host id
Can have one single physical network with up to
16,777,214 (224-2) users.
If we want more physical networks, we can divide
this one range into several smaller ranges

15. 
A class B:



Is made A two byte net id and two-byte host id
Can have one single physical network and up to
(216-2)=65,534 hosts on the network.
If we want more physical network, we can divide
this one big range into several smaller ranges.

17. 
A class C address:



is made of a three byte net id and one-byte host id
Can have one single physical network and up to 254
(28 – 2) host on that network
If we want more physical network, we can divide
this one range into several smaller range.

19. 

The internet allows a site to use variable-length sub netting.
For an example of when this may be desirable, consider a
site that is granted a class C address and needs to have five
subnets with the following of host: 60,60,60,30,30
This site can not use a subnet mask with only two bits in the
subnets section because this allows only four subnet with 62 hosts (
256/4 - 2 = 62).
 Nor can the site use a subnet mask with three bits in the subnet
section, because this allows 8 subnets with 30 hosts (256/8 -2 = 30)
 Solution for the problem: variable length subnetting.

 The router uses two different masks, one applied after the other
 First mask uses the mask with 26 1s (11111111 11111111 11111111
1100000 or 255.255.255.255.192) to divide the network into four subnets
 Then it applies the second mask with 27 1s (255.255.255.224) to one of
the subnets to divide it into two smaller subnets

21. 
An IP address has 2 parts:




The Network identification.
The Host identification.
Frequently, the Network & Host portions of the
address need to be separately extracted.
In most cases, if you know the address class,
it’s easy to separate the 2 portions.

22. 
There are default standard subnet masks for
Class A, B and C addresses