OSI Model

OSI Model

It is reference model for networking which helps in planning and troubleshooting of network. It tells that how can data move from source to destination in LAN and WAN.  It is 7 layer model which are actually 7 steps of networking.

There are few things to remember 7 layers (entire networking process) in the sequence like:

All People Seem to Need Data Processing

Please Do Not Throw Sauce Pizza Away

A  P  S   T  N  D  P

Data Encapsulation

Encapsulation means to hide the data or it is wrapping of data. It means to convert data into bits and each bit is securely transferred.

Encapsulation process:

Data -> Segment -> Packet -> Frame -> Bit

NOTE:

De-encapsulation

Convergence time

Networking Devices

1.Hub  It is networking device use to connect the different computers of same network ID, it cannot stop broadcasting, it work on layer 1 of OSI model, it has single broadcast domain and single collision domain.  There are 2 types of hub :

i)Passive hub   It has 4 ports

ii)Active hub  It has 8 ports and uplink port to cascade another hub.

2. Switch  It is networking device use to connect the different computers of same network ID, it cannot stop broadcasting, it work on layer 2 , it has single broadcast domain and multiple collision domains. It is more intelligent than hub and it is use to connect the different departments. It generally has RAM(to maintain MAC address table) and 24 ports.

There are 2 types of switch :

i)Non-manageable switch   It does not have OS and it is also known as Intelligent hub.

ii) Manageable switch  It have own OS, we can assign IP address and we can create VLAN(Virtual LAN). There are 2 categories for manageable switch :

a)Layer 2 switch  It work on layer 2, it cannot stop broadcasting, it has only one IP address for the entire switch.

b)Layer 3 switch  It work on layer 3 , it can stop broadcasting, each port has own IP address, we can create multiple VLANs, it can perform the routing function but it does not have serial interface or WIC(WAN Interface Card) and Power button.

3. Router   It is more intelligent than switch, it is use to connect the different network ID, it can stop broadcasting, it generally has memory,  OS, WIC, NAT(Network Address Translation) and work on layer 3. It has multiple broadcast domains and multiple collision domains.

4. Gateway  It is more intelligent than router, it can stop broadcasting, it can connect the different network ID and also different protocol stacks(TCP/IP and IPX/SPX).

5. Bridge  It is same as switch but it has only 2 ports.

6. Brouter   It is combination of bridge and router. Some portion use physical address and some portion use logical address for connectivity. It can work on layer 2 and layer 3. It cannot stop broadcasting.

7. Repeater  It can repeat or amplify the signals. It actually send the signals with the same speed as it has received. Maximum 4 repeater can be use in a LAN as per Ethernet standard.

NOTE: MODEM, MUX(Multiplexer), PAD(Packet Assembler De-assembler), Radware, Firewall, NTBackup devices are also use in a network.

IP Address

IP address is logical address or numerical identification of a computer.

IP version 4

It is 32 bit address in the decimal format with 4 octets. It has 2 parts-Network ID and Host ID

Network ID tell the number of network bits or tell that computer belong to which network.

Host ID tell the number of hosts per network or tell the unique identify of a computer in particular network.

Subnet Mask is  a number which can differentiate between network ID and host ID or it can tell the number of network bits. We can also use Network Prefix instead of Subnet Mask like   /8   instead of  255.0.0.0

IP address range is 0 to 255

There are 4 octets   W.X.Y.Z

Minimum Value of IP address is    0.0.0.0

Maximum value of IP address is     255.255.255.255

Octet means 8 bits   and each bit has some value like

          1        1         1         1          1        1      1     1

   128       64      32      16        8       4        2     1

                   128+64+32+16+8+4+2+1 = 255

NOTE: We can convert Binary into Decimal and vice-versa

There are different classes of IP address:

Class                          Range of W (W.X.Y.Z)

  A                              1-126

  B                              128-191                                                       

  C                             192-223

  D                              224-239                   

  E                               240-254         

 

0 is for LAN card

255 is broadcast address

127 is Loopback address use for network troubleshooting

                                                             

Class A, B, C (1-223) use for general purpose

Class D (224-239) or 224.0.0.0 to 239.255.255.255 use for multicasting purpose

Class E (240-247) reserve for future purpose

Class E (248-254) use by NASA (National Aeronautics and Space Administration)

Class       Range     Network ID        Host ID         Subnet Mask          No. of host per network

 A             1-126          W                     X.Y.Z           /8       255.0.0.0               2²⁴ - 2 =   16,777,214

 

B         128-191         W.X                       Y.Z          /16 255.255.0.0              2¹⁶ - 2   =       65,534

 C         192-223         W.X.Y                       Z          /24 255.255.255.0           2⁸ - 2    =           254

Types of IP address

1. Public IP    They are use to connect Internet directly and has to be            register by InterNIC. Except Private IP and Special IP, all are Public IP.

2. Private IP   They are use within private network (LAN and Intranet). They are use to save Public IP, to manage IP addressing etc. Range is fix for private IP:

           

                        Class A Private IP          10.0.0.1   to   10.255.255.254

                        Class B Private IP         172.16.0.1 to 172.31.255.254

                        Class C Private IP       192.168.1.1 to 192.168.255.254

3. Special IP   They are also use within private network but they are use only for special purpose

            (i) Loopback address                                              -> Any IP starting with 127.0.0.1

            (ii) ICS (Internet Connection Sharing)               -> 192.168.0.1 to 192.168.0.254

            (iii)APIPA                                                                   -> 169.254.0.1 to 169.254.255.254