To conquer the Introduction To Cisco Networking exam, and to commence the procedure of becoming an specialist network troubleshooter, you have to master the OSI model and understand what happens at each and every of the seven layers.
In this three-portion series, we'll examine every single level of the OSI model, paying specific focus to the details that will support you pass the CCNA exams and give you the foundation you require to turn into a correct networking professional.
We'll begin at the best layer, the Application layer.
It won't surprise you to uncover that the Application layer is the OSI model layer where most end users have interaction with said applications. Passing the CCNA exam is all in the particulars, though, and you need to have to know what takes place at the Application layer, as well as the typical and not-so-typical applications that run at this layer.
The Application layer's tasks incorporate identifying the remote communication partner, making sure that the required sources for communicating with that partner exist, and user authentication. If you're prompted for authentication, you're most most likely at the Application layer of the OSI model.
Preserve that in mind if asked to identify Application layer protocols. I've noticed that CCNA candidates have a tendency to identify Telnet as running at the Application layer. That's an understandable misconception, because the first factor you enter in Telnet is an IP address, and it's typically utilized to communicate with a router. However, hold in mind that Telnet is an Application layer service, not a Network layer service. You've got to authenticate to Telnet to a Cisco router in the initial place, keep in mind!
Other frequent applications that run at Layer 7 are Simple Mail Transfer Protocol (SMTP, port 25) and File Transfer Protocol (FTP, port 21).
In brief, if an end user is interacting with a system, particularly if they're getting prompted for authentication by a plan such as Telnet or FTP, they're working at the Application layer of the OSI model.
Let's take a look at the Presentation layer.
Layer 6 of the OSI model is the Presentation Layer. Whilst we don't have a great deal of interaction with this layer, you need to have to know what occurs at this layer to pass your Intro and CCNA exams.
The main objective of the Presentation Layer is generating sure that the communication that will be observed at the Application Layer is presented in the suitable format.
That's all properly and very good, but what does it mean? J Have you ever opened a document with MS Word and gotten screens and screen of garbage? That's a presentation layer dilemma - the plan being utilized to open the document is unable to present the data in an proper format.
The three major tasks of the Presentation layer:
1. Compatibility with the operating program.
2. Proper encapsulation of information for network transmission.
3. Data Formatting (ASCII, binary)
Encryption and compression of information is also handled at the presentation layer.
Let's hold functioning our way down the OSI Model. Subsequent up, the Session Layer!
The Session layer of the OSI model basically acts as the manager for the whole model. Some have named it the PHB (Pointy-Haired Boss) of the OSI model if that assists you remember its role, that's fine with me!
The Session layer establishes, manages, and tears down connections among applications. The Session layer utilizes port numbers to hold multiple conversations between two finish points separate. You may possibly have heard the term effectively-recognized port-numbers before. That term refers to port numbers that are usually-utilised and static in that they use the exact same port numbers every time. You'll be expected to know common well-identified port numbers to pass your Intro exam, such as 23 for Telnet and 21 for FTP.
That's about all there is to Layer 5, the Session Layer. From right here on out, there's more you need to have to know about every single layer, and that begins with Layer 4 - the Transport Layer. We'll take a look at that layer in Component II of this OSI tutorial.
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, house of over one hundred totally free certification exam tutorials, such as Cisco CCNA certification test prep articles. His exclusive Cisco CCNA study guide and Cisco CCNA coaching is also offered!
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