NETWORKING FOR ETHICAL HACKING | OSI MODEL

THE OSI MODEL

The Open Systems Interconnect (OSI) model describes how networks communicate. It describes the various protocols and activities. It also states how the protocols and activities relate to each other. This model is divided into seven layers. It wasa originally developed by the International Organisation for Standardization (ISO) in the 1980's.

 

Let's look at each of the layers by top down approach. There are several protocols(marked red) implemented in each layer to perform the tasks.

7.APPLICATION layer interfaces directly to applications and performs common application services for application processes. POP, SMTP, DNS, FTP, Telnet, HTTP

6.PRESENTATION layer relives the application layer of concern regarding syntatical difference in data representation within the end-user system. Network Data Representation (NDR), Lightweight Presentation Protocol (LPP). 

5.SESSION layer provides the mechanism the dialouge between end user application processes. NetBIOS

4.TRANSPORT layer provides end-to-end communication control. TCP, UDP

3.NETWORK layer routes information in the network. IP, ARP, ICMP

2.DATA LINK layer describes the logical organisation of data bits transmitted on a particular medium. Data link layer is divided into two sub-layers - Media Access Control (MAC) and Logical Link Control Layer (LLC). SLIP, PPP

1.PHYSICAL layer describes the physical properties of various communication media as well as the electrical propertied and interpretation of the exchanged signals. The physical layer is the  actual NIC and the Ethernet cable. IEEE 1394, DSL, ISDN

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