OSI Model for Cisco Networking

While you may not use the OSI model every day, you should be familiar with it, specifically when working with Cisco switches and routers (which operate at Layer 2 and Layer 3, respectively). Here are some of the items that operate at each level of the OSI model:

Layer	Description	Examples
7. Application	Responsible for initiating or services the request.	SMTP, DNS, HTTP, and Telnet
6. Presentation	Formats the information so that it is understood by the receiving system.	Compression and encryption depending on the implementation
5. Session	Responsible for establishing, managing, and terminating the session.	NetBIOS
4. Transport	Breaks information into segments and is responsible for connection and connectionless communication.	TCP and UDP
3. Network	Responsible for logical addressing and routing	IP, ICMP, ARP, RIP, IGRP, and routers
2. Data Link	Responsible for physical addressing, error correction, and preparing the information for the media	MAC address, CSMA/CD, switches, and bridges
1. Physical	Deals with the electrical signal.	Cables, connectors, hubs, and repeaters

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