Subnetting

SUBNETTING

What is subnetting ?

Sub netting allows creating multiple networks from a single address block.

Why do we use subnetting ?

We use sub netting for:-
(a) Maximize addressing efficiency.
(b) Extend the life of IPv4.
(c)Public IPv4 addresses are scarce.

How do we use subnetting ?

We use it for transforming host bits into network bits creating additional networks from a single address block.

Formula and Variables

h – Number of host bits.
b – Number of host bits transfer into network bits.
n – Number of network bits.
2^b – Number of networks resulting from the subnetting.
2^h-2 – Number of hosts per new network. 

Example of subnetting:-

Subnetting base address – 192.168.1.0/24
11111111   11111111   11111111   00000000

Transform 1 host bit into a network bit.
11111111   11111111   11111111   10000000
2^b networks
2^h-2 hosts per new network.
New prefix length /25
     255.255.255.128

How we find no. of hosts in 1 bit?

11111111   11111111   11111111   1|0000000
                                    Subnet mask – 255.255.255.128

2^7-2= 126
255.255.255.0/25 – Network ID
255.255.255.128/25 – Broadcast ID 

Transform 2 host bits into network bits.
11111111   11111111   11111111   11000000
2^b network
2^h-2 host per new network
New prefix length /26     255.255.255.192

How we find no. of hosts in 2 bit?

11111111   11111111   11111111   11|0000000
                                    Subnet mask – 255.255.255.192

2^6-2= 62
255.255.255.0/26 – Network ID.
255.255.255.64/26 – Network ID.
255.255.255.128/26 – Network ID.
255.255.255.192/26 – Broadcast ID.  

	SUBNET MASK
Mask	Number of Hosts	Host Bits
255.255.255.0	254	8
255.255.255.128	126	7
255.255.255.192	62	6
255.255.255.224	30	5
255.255.255.240	14	4
255.255.255.248	6	3
255.255.255.252	2	2

IP ADDRESS

What is IP address?
IP Address is a 32 bit address that is used to uniquely identify a computer on a network.

Why required IP Addressing in Decimal Number System?
Ans: - Human Never remember Binary Bits of IP Address Format.

How do we write IP address & How to convert?
32bit IP Address in Binary Bit example: - 11000000101010000110010100101101 

Step 1: These dots are separated for 8 bit each.

11000000.10101000.01100101.00101101
0= Low Bit
1= High Bit
0100= 4 bit nibbles
00010111= 1 bytes
8 Bits = 1 Octal

Convert Process Chart:-
1        1     1     1     1    1    1   1 
128   64   32   16   8   4    2   1

1       1     0      0    0   0    0   0 = (128+64= 192)

Each Octal Number converted in Decimal Number:- 

11000000=192
128+64+0+0+0+0+0+0=192

10101000=168
128+0+32+0+8+0+0+0=168

01100101=101
0+64+32+0+0+4+0+1=101

00101101=45
0+0+32+0+8+4+0+1=45

So the IP address is  :- 192.168.101.45

There are two parts in IP address.


 Network ID: - 
The network ID portion of the IP address identifies the network where the computer fit.

Host ID: -  
The host ID portion of the IP address uniquely identifies the computers on its network.

Example: -           192.168.10.1
                         network ID     Host ID

 Subnet mask: -   255.255.255.0
                          network ID    Host ID

These IP address are divided into classes.

Address class	Octets range	Octets of network	Number of network	Host per network	Subnet mask
A	1-127	1	126	16,777,214	255.0.0.0
B	128-191	2	16,384	65,534	255.255.0.0
C	192-223	3	2,097,152	254	255.255.225.0
D	224-239	-	-	-	-
E	240-247	-	-	-	-

Private (reserved) address
10.0.0.0 to 10.255.255.255
172.16.0.0 to 17.31.255.255
192.168.0.0 to 192.168.255.255

Private address are used for testing, training and internally for private use.

OSI / TCP

 What is OSI?

The open system interconnection model (OSI) is a conceptual model that characterizes and standardizes the internal function of a communication system by partitioning it into abstraction layers. The model is a product of the open system interconnection project at the international organization for standardization (ISO), maintained by the identification ISO/IEC 7498-1. 

A model groups communication functions into seven logical layers.

OSI(Open System Interconnect)

Application

Presentation

Session

Transport

Network

Data link

Physical

We study about all layers of OSI one by one:-
(1)Application –This layer provides the user communication that creates information & data.
     Example: - FTP protocol

(2)Presentation –This layer considered with the format of data exchange between the end systems.

(3)Session –This layer allows user a different machine to create session between in them. This layer also binds the different streams like audio signal and video signal.    

(4)Transport –This layer considered with end to end communication message. It receives the data from session layer and divides it into smaller units called as message. These messages are passed on to network layer and then these messages are passed down to upper layer.

(5)Network –This layer considered to routing of packets to correct destination.

(6)Data Link –This layer considered transmission of error free data in the form of terms.

(7)Physical layer –This layer considered with transmission on raw bits over the communication link.  

How two PCs are connected on network.

OSI – Open System Interconnect
Application-----------------------	---------------------------------------	Application
Presentation---------------------	---------------------------------------	Presentation
Session-----------------------------	---------------------------------------	Session
Transport-------------------------	---------------------------------------	Transport
Network---------------------------	--------------Network -----------	Network
Data link--------------------------	---------------Data link----------	Data link
Physical---------------------------	--------------Physical------------	Physical

What is TCP?

Transmission control protocol. The TCP is one of the core protocols of the internet protocol suit, and is so common that the entire suit is often called TCP/IP. TCP provides reliable, order and error-check delivery of a stream of octets between programs running on computers connected to a local area network, intranet or the public internet. It resides at the transport layer. Web browser use TCP when they connect to servers on the World Wide Web, and it is used to deliver email and transfer files from one location to another. HTTP, HTTPS, SMTP, POP3, IMAP, SSH, FTP, Telnet and a variety of other protocols are typically encapsulated in TCP. Applications that do not require the reliability of a TCP connection may instead use the connection less user Data-gram Protocol (UDP), which emphasis low-overhead operation and reduced latency rather than error checking and delivery validation.

It is also divided into four layers.

TCP
Application	HTTP , SMTP    DNS , RIP.
Transport	TCP(Reliable) , UDP(Unreliable).
Internet	IPv4 ,  IPv6.
Network Interface	Ethernet , Wireless , Frame relay , ATM.

Layer 2:-Switches work on layer 2 devices. It supports local area network.

Layer 3:-Routers work on layer 3 devices. It supports world wide web.