Decyphering the OSI model of networking: 7 layers of bean dip (2022)

Posted: January 9, 2020 | | by Glen Newell (Sudoer alumni)


Decyphering the OSI model of networking: 7 layers of bean dip (1)

At this time of year, many sysadmins thinkabout holidays, football games, and party food. Food is the defining factor in the success of a good holiday or sports gathering. The best parties have a little something for everyone and a few items that everyone likes,but there are things you have to have, like ice for drinks. And desserts. And chips. And dip. Thebest parties have the ultimate snack: seven-layer bean dip (7LBD). What makes 7LBD special is that each layer is in the right order and in the right quantity.

Speaking of which, we can say the same thing about understanding and troubleshooting network issues. (See what I did there?) In 1984, the International Standards Organization (ISO) published the document Open Systems Interconnection Reference Model, which is commonly referred to as the OSI model today. The idea was to address the increasing need for a set of network communication standards that could be used to engineer the interoperability of the rapidly evolving technologies in use for connecting computers.

The OSI model consists of sevenlayersand two sets of standards:One describing what each layer refers to, and another establishing an existing set of protocols for each layer.As a system administrator, even if you don’t work directly with your infrastructure'snetworking components, you probably use this model all the time—even if you don’t know it. So, you will be better at your job if you know and understand how this model works, and how to apply it to troubleshooting.

So, what’s the recipe?

When I first learned about the OSI model, I had to learn the names by memorizing them:

  1. Physical
  2. Data
  3. Network
  4. Transport
  5. Session
  6. Presentation
  7. Application

I think I wrote the name of each layer on my fingers and made cool charts. Since then, I’ve used the information enough that it’s no longer a struggle to remember where to look next. Just like the world’s greatest snack tray, I just know the model, and that makes me much more successful.

Let’s go through each layer.

(Video) what is TCP/IP and OSI? // FREE CCNA // EP 3

Layer 1: Physical

In any troubleshooting, the most important principle is to start simple and low.Is it plugged in?Is the link light green? I always think of Layer 1 as the hardware layer. Here, wethinkabout electrons getting where they need to be and in the right order.

This layer of the OSI model refers to things like signaling and voltage. The associated protocols would be Ethernet and newer technologies like Bluetooth. When we work with network topologies, we are looking at the physical layer: How the bits move from one location to another.

To be clear, this layer is not cables and network cards. It’s the stuff that makes them useful. When troubleshooting if you can access a webpage, you need to know that this layer provides a path between the user and the server.

Layer 2: Data

The data (or data link) layer is where the bits from the physical layer get organized into something useful, but still somewhat primitive. This is where these bits start to become useful as information. Wedon't thinkabout what’s getting transferred so muchas we do abouthow. This layer is where flow control and error correction happens, and also where devices can communicate with one another usefully.

Layer 2 is divided into two sublayers. The first is the medium access control (MAC) layer, which involves hardware addressing and access control. The second is the logical link layer, which provides the ability to create a logical connection between media.

A network hub (which is rare now, but they used to be more common due to their simplicity) or the switch used in many offices for easy local networking,is what we call a Layer 2 device.It simply creates a connection and forwards all of the data it has to all of the physical connections it’s associated with. When we troubleshoot this layer, we connect to a network and determine if that network is the right collection of devices from here to there.

Layer 3: Network

Now we'vereached the first really interesting stuff. The network layer is where actual communication takes place between two devices. This layer is where we create packets and addresses, and have at least some control over the bits.

In this layer, we define how much data we can move at a time, what’s in each chunk of data, and where that data goes. It’s where we create the envelope. The protocol associated with this layer is the Internet Protocol (IP). Most modern commercial enterprise network equipment operates on this layer. A router, or "layer 3 switch,"is the hardware that does this work. We test this layer by checking that we have an address on the network we are connected to, and that we can see the address of the device we are trying to connect to.

(Video) OSI Model and its 7 Layers Explained in Detail | OSI Animation | Open System Interconnection Model

The ping command is a network layer utility.

Layer 4: Transport

If Layer 3 is the envelope, then Layer 4 is the postal service. In this layer, we do things like segmentation and reliability management. The protocols associated with Layer 4 are TCP and UDP. We can say:"Do this when you receive this packet."We can even keep track of what other chunks of data (packets) are supposed to be with this oneand specify what to do if they haven’t arrived, or aren’t in the right order.

In this layer, we can prove that we see the target deviceand that we should be able to communicate, but we are concerned now with being able to connect. A good test here is to use telnet or netcat to see if the server is "listening"and responding to requests for a connectionand ifwe can get an actual response.

Layer 5: Session

At this point, we have arrived at the target host. The session layer is where connections are defined and managed. It's where we managethe dialog between devices or applications. Layer 5the first handoff of our data from the operating system to a process or application on the local device, or in the host. Here, we can start or end a connection,or make Remote Procedure Calls (RPCs) between applications on different hosts,with actions such as mounting a filesystem.

In Layer 5, we might try another application if we can’t get a webpage. Both FTP and SSH are useful here if they are available. Note that we still lookonly at what we have from the previous layers, so in Layer 5 we have an IP address rather than a website name (more on this in the application layer). Here, we often lookat whether we have permission to connector have access to a filesystem or application.

Layer 6: Presentation

By Layer 6,we have officially handed off of the data we received in Layer 2, recognized in Layer 3, reassembled and made sense of in Layer 4, and distributed to the right place on the host in Layer 5. In the presentation layer, wepresentdata to be interpreted as code, or instructions. We are no longer simply moving bits, we are using them for something at the destination.

This layer is where we can do things like encryption (SSL). This layer is also where we can see XML and HTML code being presented for translation by a web browser. The bits are in the right order, we are talking to the web browser, and we need to make sure the browser can understand and use what we sent. Our troubleshooting deals with things like certificates.

(Video) ITN04 Physical Layer

Layer 7: Application

This is it, the end of the line. We now have data that traversed the network and successfully made it all the way up the stack to an actual program or application to do the job we sent it to do. Our little team of packets is making something happen.

In the case of a webpage request, the HTML gets rendered into a page, possibly like the one you are looking at now. By this point, we lookat what the target application (i.e., a web browser) is doing. DNS, which is used to translate a webpage's name into an IP address, is an application layer protocol—it’s an application that translates instructions.

In this layer, we can check that when we ask for an address, we can see the webpage or application we expect to see. We look at the application’s configurationand at the compatibility of the software versions being used.

Wrapping up

So, there you have it: The recipe for network troubleshooting. Hopefully, you can use this recipe to make your network a successful gathering and keep all of your infrastructure guests happy.

(My award-winning bean dip, on the other hand, is a secret. You’ll have to find your own recipe for that.)

Want more on networking topics? Check out the Linux networking cheat sheet.

(Video) What is OSI Model?


What are the 7 layers of OSI model in networking? ›

In the OSI reference model, the communications between a computing system are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

How do you remember the 7 layers of the OSI model? ›

OSI Layers Mnemonic
  1. Layer 1: Physical = Please.
  2. Layer 2: Data Link = Do.
  3. Layer 3: Network = Not.
  4. Layer 4: Transport = Touch.
  5. Layer 5: Session = Steve's.
  6. Layer 6: Presentation = Pet.
  7. Layer 7: Application = Alligator.
8 Oct 2020

Which of the following layer in the 7 layer OSI model is responsible for data encryption? ›

Encryption (and compression) is handled at the Presentation Layer, pg. 435 CISSP Official Study Guide 7th ed. While SSL and TLS do operate at the Transport Layer, encryption is listed at the Presentation Layer.

Which layer of the 7 layer OSI model works with frames? ›

Data-link layer is the second layer from the bottom of the OSI Reference Model. The main function of the data-link layer is to perform error detection and combine the data bits into frames.

What is Layer 7 data called? ›

Layer 7 refers to the top layer in the 7-layer OSI Model of the Internet. It is also known as the "application layer." It's the top layer of the data processing that occurs just below the surface or behind the scenes of the software applications that users interact with.

What is the purpose of the 7 layer OSI reference model in industry? ›

The purpose of the OSI reference model is to guide technology vendors and developers so the digital communications products and software programs they create can interoperate and to promote a clear framework that describes the functions of a networking or telecommunications system that's in use.

Which OSI layer is most important? ›

Layer 3, the Network Layer

This is the most important layer of the OSI model, which performs real time processing and transfers data from nodes to nodes.

What is the easiest way to memorize the OSI layers? ›

Using the OSI model, the communications between computing systems are done through seven abstraction layers; it's easy to remember the sequence of OSI Model 7 Layers using this simple sentence: "All people seem to need data processing."

Why is it important to fully understand the OSI model in networking? ›

The OSI allows you to identify threats across your entire tech stack. The OSI model has been used for decades to help IT experts understand networking and troubleshoot issues that may arise at any stage in the networking process.

Which of the following is the correct order of 7 OSI layers from highest down to lowest? ›

The layers are: Layer 1—Physical; Layer 2—Data Link; Layer 3—Network; Layer 4—Transport; Layer 5—Session; Layer 6—Presentation; Layer 7—Application.

Which of the following is the correct order of the 7 layers of the OSI model beginning at layer 1? ›

An OSI model consists of seven different layers which are typically described from the top to bottom. In order from seven to one, the layers are as follows: application, presentation, session, transport, network, data link, and physical.

Which layer of the 7 layer OSI model that has the mechanism to ensure the data is complete and arrives in correct order at the destination? ›


The fourth layer of the OSI model ensures complete and reliable delivery of data packets. The transport layer provides mechanisms such as error control, flow control, and congestion control to keep track of the data packets, check for errors and duplication, and resend the information that fails delivery.

What is OSI model explain with diagram? ›

OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. OSI consists of seven layers, and each layer performs a particular network function.

What protocols are used in each layer of OSI model? ›

TCP/IP Protocol Architecture Model
OSI Ref. Layer No.OSI Layer EquivalentTCP/IP Protocol Examples
5,6,7Application, session, presentationNFS, NIS+, DNS, telnet , ftp , rlogin , rsh , rcp , RIP, RDISC, SNMP, and others
4TransportTCP, UDP
3NetworkIP, ARP, ICMP
2Data linkPPP, IEEE 802.2
1 more row

What is OSI model with example? ›

The Physical layer of the OSI model is responsible for the transfer of bits — the 1's and 0's which make up all computer code. This layer represents the physical medium which is carrying the traffic between two nodes. An example would be your Ethernet cable or Serial Cable.

What is Layer 7 protection? ›

Layer seven refers to a layer of security built into the open systems interconnect model. This is the highest level of security in the application level that supports end-user applications and processes.

What is Layer 7 load balancing? ›

Layer 7 load balancing allows the load balancer to route a request based on information in the request itself, such as what kind of content is being requested. So now a request for an image or video can be routed to the servers that store it and are highly optimized to serve up multimedia content.

How a packet moves through the 7 layers of OSI model? ›

Then, the packets are sent from the network layer to the data link layer, where packets are further broken down into frames. The frames are sent to the physical layer where data is converted to bitstreams of ones and zeros and transferred across a medium such as wireless connections or cables.

What are the 7 layers in order? ›

From lowest-level to highest-level they are:
  • #1. The Physical Layer.
  • #2. The Data Link Layer.
  • #3. The Network Layer.
  • #4. The Transport Layer.
  • #5. The Session Layer.
  • #6. The Presentation Layer.
  • #7. The Application Layer.

What is the purpose of OSI model? ›

The OSI model helps network device manufacturers and networking software vendors: Create devices and software that can communicate with products from any other vendor, allowing open interoperability. Define which parts of the network their products should work with.

Why is it called OSI? ›

This model is called the ISO OSI reference model because it deals with systems that open for communication to the other system. So, An OSI (open system interconnection )reference model is a set of protocols that allows any two different systems to communicate regardless of their underline architecture over the network.

Which layer is called the heart of the OSI model? ›

The transport layer is the heart of the OSI model. The data is sent through the physical layer to the application layer (at the sender's end).

Should I learn the OSI model? ›

It is a tool for understanding how networks function. Once you learn the OSI model, you will be able to further understand and appreciate this glorious entity we call the Internet, as well as be able to troubleshoot networking issues with greater fluency and ease.

How many protocols are used in the application layer? ›

Few of Application layer protocols are described below:
  • Domain Name System. The Domain Name System (DNS) works on Client Server model. ...
  • Simple Mail Transfer Protocol. ...
  • File Transfer Protocol. ...
  • Post Office Protocol (POP) ...
  • Hyper Text Transfer Protocol (HTTP)

What are the benefits of using the OSI model? ›

The advantages of the OSI model are

It distinctly separates services, interfaces, and protocols. Hence, it is flexible in nature. Protocols in each layer can be replaced very conveniently depending upon the nature of the network. It supports both connection-oriented services and connectionless services.

Why is the OSI model the best? ›

It provides a straightforward way to understand and communicate the process through which devices or components are supposed to work with. Also, OSI reduces complexities, supports interoperability, facilitates modular engineering, and makes it easy to adapt to different types of networking protocols.

Why is the network layer most important? ›

Network layers are important because they enable developers to work at their appropriate levels.

Which layer of the OSI model requires the highest security consideration justify your answer with examples? ›

The Network and Transport layers of the OSI model are where the most common security precautions take place — this layer is where routers and firewalls are implemented.

Which of the following is the correct top down order of the OSI model? ›

The OSI model layers are typically described from the top layer down. The layers are described as Application, Presentation, Session, Transport, Network, Data Link, and Physical.

Which layer of the OSI model contains all the services or protocols that are needed by application software or the operating system to communicate on the network? ›

Which layer of the OSI model contains all the services or protocols that are needed by application software or the operating system to communicate on the network? all aspects of physically moving data from one computer to the next. The packet becomes this in the Data Link layer.

Which two functions are implemented at the application layer of the OSI model? ›

Application layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication.

What layer in OSI model that is close to the end user and interacts with software application? ›

The application layer is the OSI layer closest to the end user, which means both the OSI application layer and the user interact directly with the software application.

What is the name of a data unit used at the OSI physical layer? ›

A protocol data unit (PDU) is an open-system interconnection (OSI) term used in telecommunications that refers to a group of information added or removed by a layer of the OSI model.

What is the correct order of data representation in OSI model Mcq? ›

Explanation: The seven layers in ISO OSI reference model is Application, Presentation, Session, Transport, Network, Data link and Physical layer.

Which protocol is used in data link layer of an OSI model Mcq? ›

Explanation: There are many data link layer protocols. Some of them are SDLC (synchronous data link protocol), HDLC (High level data link control), SLIP (serial line interface protocol), PPP (Point to point protocol) etc. These protocols are used to provide the logical link control function of the Data Link Layer.

What is the application layer in OSI model? ›

The application layer is actually an abstraction layer that specifies the shared protocols and interface methods used by hosts in a communication network. Application Layer helps us to identify communication partners, and synchronizing communication. This layer allows users to interact with other software applications.

Which layer of the OSI model is the most important? ›

Layer 3, the Network Layer

This is the most important layer of the OSI model, which performs real time processing and transfers data from nodes to nodes. Routers and switches are the devices used for this layer that connects the notes in the network to transmit and control data flow.

How do you identify if a computer is in a network? ›

How to manually identify unknown devices on a network
  1. Open the Command prompt or Terminal in your Windows, Linux, or macOS system.
  2. Search all the network settings, such as default gateway and IP address, through the command prompt.
  3. Type the command "arp -a" to view the list of all IP addresses connected to your network.

Which layer in OSI model performs network routing? ›

Layer 3, the network layer, is most commonly known as the layer where routing takes place. A router's main job is to get packets from one network to another.

Why are the 7 layers of the OSI model be always arranged in order? ›

In the OSI model, layers are organized from the most tangible and most physical, to less tangible and less physical but closer to the end user. Each layer abstracts lower level functionality away until by the time you get to the highest layer.

Which are the 7 layers of OSI model explain the function of each layer What is the TCP IP model write the difference between OSI and TCP IP model? ›

TCP/IP vs OSI: What are the different layers? The TCP/IP Model comprises four layers: Network Interface, Internet, Transport and Application. The OSI Model comprises seven layers: Physical, Data Link, Network, Transport, Session, Presentation and Application.

What is OSI layers explain with example and works? ›

Seven layers of the OSI Model
GroupLayer NumberDescription
Top Layers5Initiate and terminate a session with the remote system
Bottom Layers4Break the data stream into smaller segments and provide reliable and unreliable data delivery
3Provide logical addressing
2Prepare data for transmission
3 more rows
13 May 2021

What is OSI layer with example? ›

The Physical layer of the OSI model is responsible for the transfer of bits — the 1's and 0's which make up all computer code. This layer represents the physical medium which is carrying the traffic between two nodes. An example would be your Ethernet cable or Serial Cable.

What is the importance of knowing the OSI layers? ›

In theoretical discussions, the OSI Reference Model helps you understand how networks and network protocols function. In the “real world”, it also helps you figure out which protocols and devices can interact with each other.

What are the functions of the layers of the OSI layer define each function? ›

Characteristics of OSI Model

The upper layer deals with application issues using the software. Application layers are nearest to the users. The layer above another one refers to the upper layer. The lower layer deals with data transport using hardware and software.

What is OSI model explain the functions and protocols and services of each layer? ›

OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. OSI consists of seven layers, and each layer performs a particular network function.

What is OSI short answer? ›

The Open Systems Interconnection (OSI) model describes seven layers that computer systems use to communicate over a network. It was the first standard model for network communications, adopted by all major computer and telecommunication companies in the early 1980s.

How does OSI model transfer data? ›

How Data Flows Through the OSI Model. Data flows from layer 7 down to layer 1 from the sender, and then flows from layer 1 to layer 7 on the recipient device. The simplest example of communication flow through the OSI Model is an email application.

What is layer very short answer? ›

A layer of a material or substance is a quantity or piece of it that covers a surface or that is between two other things.

How does OSI model work? ›

The OSI reference model describes how data is sent and received over a network. This model breaks down data transmission over a series of seven layers. Each layer has a responsibility to perform specific tasks concerning sending and receiving data. All of the layers are needed for a message to reach its destination.

What is OSI how it works? ›

OSI model is a layered framework that allows communication between all types of the computer system. It has seven layers. OSI model is introduced by ISO(International Organization for Standardization) in 1984. Each layer has its own functionalities and calls upon the services of the layer just below it.


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