The document discusses sub netting and IP addressing. It explains that in sub netting, a network is divided into smaller subnetworks, with each having its own subnet address. It also notes that dividing a network into subnets does not increase the number of available IP addresses, as two addresses are reserved in each subnet. The document then provides details on IP address classes and how variable length subnetting can be used to allocate addresses when the default subnetting does not meet network needs.

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