1. Introduction
Hello and welcome to this course on Juniper Networks Certified Associate JNCIA-Junos JN0-104. I’m really happy to have you here.
First, let’s talk about me. My name is Shyam, and I’m a technical instructor by profession. I train students on networks, firewalls, security and cloud. Over the past few years, I’ve had the opportunity to teach thousands of students and help them pass the JNCIA-Junos exam. I’m confident that you will be able to do the same. By the way, that’s me posing in front of the Tower Bridge in London. This was about a year ago. I’ve lost a lot of weight since then.
OK, now let’s talk about the course. This course will help you prepare for the JNCIA-Junos JN0-104 Certification Exam. In this course, we’ll start with the fundamentals of networking before moving on to the basics of Junos. And we’re going to start with really basic topics like the OSI model, TCP/IP model, MAC addresses, VLANs, collision domains and broadcast domains, IPv4, IPv6 subnetting and some other topics of networking before we move on to the basics of Junos. So, if you’re just new to networking and have no idea about the basics, that’s OK. We’re going to cover those items first, lay a solid foundation before we move on to the advanced topics. If you’re a beginner to Junos, or if you’re a beginner to networking, or if you have some hands on experience, this course is ideal for you.
Now, why should you take this course? This course will help you establish a strong foundation on networking concepts like we just discussed. We’re going to focus on the basic topics, the basic networking topics before we move on to advance Junos topics. You will also understand the fundamentals of Juniper network devices. We’ll learn how to administer and configure a Junos environment. And also, JNCIA-Junos is the first in the Juniper certification list. So this is the right place to begin. Above all, by the end of this course, you’ll be ready to pass the JNCIA-Junos Certification Exam.
Now, let’s talk about the target audience. This course is intended for students preparing for the JNCIA-Junos JN0-104 Certification Exam. This course is also useful for students who are new to networking and for network administrators. Talking about Juniper certification tracks, JNCIA-Junos, the course that we’re talking about right now, is the starting point for three certification tracks: data center, enterprise routing and switching, and service provider routing and switching. Once you complete JNCIA, you can move on to advance certifications like JNCIS, which is the specialist level certification; JNCIP, which is the professional level certification; and JNCIE, which is the expert level certification. You will find this information on Juniper’s Web site, which is juniper.net/certification.
Now, let’s talk about the exam. The exam code is JN0-104. It’s a written exam that you can take online from your home or office or at a PearsonVUE center. It is a 90-minute exam consisting of 65 multiple choice questions and pass or fail status is available with the score immediately. Once you pass the exam, the certification is valid for three years. From my personal experience, I can say that the exam is not very difficult. There is a learning curve. You will need to learn a lot of concepts. But if you know them well, you can easily pass the exam. On a scale of 10, I would rank the difficulty of this exam as seven, so it’s not very difficult. It does have a learning curve, but if you know the concepts really well, you can pass the exam on the first attempt.
Now, let’s talk about exam objectives. There are seven sections that we need to cover. Starting with networking fundamentals, we’ll then move on to a Junos operating system fundamentals; we’ll talk about user interfaces, configuration basics, operational monitoring and maintenance, routing fundamentals, and routing policy and firewall filters.
Now, let’s talk about the strategy to use to prepare for the JNCIA-Junos exam so you can pass at the first attempt. Number one – use technical material like this course and Juniper’s official documentation to learn the exam topics. All the topics required for the examination are covered in this course, but I strongly recommend that you also supplement this with Juniper’s official documentation. Number two – get hands-on lab time. There’s a couple of ways you can do this. Number one – you can buy a physical general appliance, and if you’re interested, I recommend looking at eBay. Sometimes, you will find used SRS devices for throwaway prices. The other option is to rent lab time. Just go online and look for online Juniper Labs, and you should find some providers. And lastly – use a practice test to gain exam confidence. I can’t stress this enough. Using a practice test may make all the difference. You may know all the topics in and out, but when you sit for the exam, when you see questions, it may just throw you off. By using a practice test, you’ll be ready and you will know what to expect at the examination. So, I strongly recommend that you use a practice test to make sure you pass the exam at the first attempt. And lastly, if you’d like to connect with me, you will find me on LinkedIn (linkedin.com/in/shyamraj87).
Now, let’s get started with the first topic.
2. OSI Model
Let’s start with the first topic of networking fundamentals known as the OSI model. If you’ve taken any networking course or if you’ve read any networking textbook in the past, you would have noticed that the OSI model is discussed right in the beginning. And that’s because the OSI model is a fundamental topic for networking. Let’s talk about it.
It stands for Open Systems Interconnection. The history of the OSI model dates back to the earliest days of network communication when every vender had their own protocol for their equipment. This would mean that if you connected to devices from two different vendors, they wouldn’t talk because there was no common protocol. So, in the 197zeros, the International Standards Organisation, also known as ISO, came forward to standardize network communication. The goal here was to have a common protocol irrespective of the underlying hardware or manufacture.
The OSI model divides network communication into seven layers. The entire process of communicating over the network is broken down into seven layers and each layer is assigned a certain set of functions. It is important to keep in mind that the OSI model is a purely logical concept. The layers of the OSI model do not represent any networking components. Network components may belong to different layers of the OSI model, but the layers of the OSI model do not directly represent any network components. The OSI model looks like this. Let’s start from the bottom. The first layer is physical layer. Then we have the data link clear. Then we have the network layer, transport layer, session layer, presentation layer, and application layer.
There are some mnemonics available to remember the layers in order. I found a couple of them on the Internet. The first one is ‘Please do not throw sausage pizza away.’ And the second interesting one I found was ‘People don’t need these stupid packets anyway.’ You could use any mnemonic to remember the layers in the order.
Now let’s talk about each of these layers in detail. We’ll start with the first layer, which is the physical layer. This is the layer where data arrives in raw format, which is bits made up of zeros and ones. The physical layer is responsible for defining the electrical and physical specifications of hardware used to communicate over network. So, that means it is responsible for defining standards for cables, connectors, frequencies of wireless signals, voltage specifications, etc.
The physical layer also defines standards for the type of communication. So, we have three types of communication. Simplex, which is one-way only. Think of a radio broadcast. The second type of communication is half duplex, which is two-way, but you can only send or receive at a time. Think of a walkie-talkie. The third one is full duplex, which is two-way communication where you can send and receive data at the same time. Think of a phone call.
So it’s the physical layer that’s responsible for defining standards for the type of communication. There are some devices that operate at the physical layer. This includes hubs, network interface cards, and repeaters.
Let’s now talk about the second layer, which is the data link layer. The bits received by the physical layer, when they move up one level, they reach the data link layer and they are now transformed into frames. And that’s because some headers are added on top of the bits and now they become frames. The data link layer is responsible for communication over the local area network, also known as LAN, or the same network. You’ll hear network administrators say ‘This is a Layer 2traffic.’ That means it is traffic this time for the same network and it is handled by the data link layer.
The data link layer is also responsible for physical addressing of devices. So, every network device will have a physical address which is burned onto the chip, and that’s known as the MAC address. That is a function of the data link layer. Other functions include flow control, which is synchronizing the sending and receiving of frames, and also error control.
The protocols that operate at the data link layer include Ethernet, which is a very popular protocol, frame-relay, token ring, and fiber distributed data interface, also known as FDDI.
The devices that operate at this layer include bridges and Layer 2 switches.
Let’s now talk about the third layer, which is the network layer. The frames that were present at the data link layer, when they move one level up, some headers are added on top of that and it is now transformed into packets.
The network layer is responsible for logical addressing of devices. This is done using IP addresses. So, IP addresses, which could be IPv4 or IPv6, are a function of the network layer. We call them as logical addresses because they are not tied to a device. You can take an IP address from one device and assign it to another device, which is why we call them as logical addresses. While MAC addresses are burnt onto the chip, so we call them as physical addresses.
So, logical addressing is a function of the network layer. It is also responsible for routing packets and also for fragmentation and reassembly of packets.
The protocols that operate at this layer include IPv4, IPv6, ICMP, IPsec, etc. And the devices that operate at this layer include Layer 3 switches, routers, firewalls, etc.
Now, let’s talk about the fourth layer, which is the transport layer. The packets at the network layer, when they move one level up, some headers are added on top of them and they are now transformed into segments.
The transport layer is responsible for a very important function, which is to provide a transport protocol such as TCP and UDP. TCP is used when you need a reliable data connection because it is a connection-oriented protocol. While UDP is a connectionless protocol, so it operates faster and is used for real time services such as voice and video.
The transport layer is also responsible for another important function, which is process separation. This allows multiple programs on the same device to communicate using port numbers. Think about this. Think about the browser that you may be using right now. You may have multiple tabs open on the browser, but every tab is able to correctly communicate with its own server without the traffic from other taps getting mixed up. That is a function of the transport layer. This process separation is a function of the transport layer, and this is done using port numbers.
Moving up, we have the session layer. This is responsible for establishing and controlling sessions between the sender and the receiver. It’s also responsible for synchronizing the session. And this is done using sequence numbers. The protocols that operate at this layer include NetBIOS, SOCKS and network file system, also known as NFS.
Moving up, we have the presentation layer. This is responsible for presenting or formatting the data received in generic format from the lower layers into well-known formats. Examples include JPEG, MPEG, etc. We as end users are used to viewing data in well-known formats like MP4, JPEG, etc., and we do not interact with data in other formats like packets, or frames, or bits in the form of zeros and ones. So, it’s the presentation layer that’s responsible for taking the data that comes from these lower layers in the form of packets and segments and transforming that into well-known formats that we can understand.
The presentation layer is also responsible for compression and encryption.
The last layer is the application layer. This is responsible for providing an interface between the applications and the underlying network. An important thing to keep in mind, the application layer is not the same as the applications used on the computer. The application layer provides an interface for the applications, but does not directly represent the applications that you run on your computer. It provides the services or protocols that allow applications to communicate with the network stack.
Protocols at this layer include DNS, HTTP, FTP, etc.
The functions that we discussed here are not the only functions performed by these layers. The layers actually perform a lot more functions. But at the JNCIA level, this is good enough for us to know to give us a good start.
The functions of the OSI model are not important from the JNCIA examination perspective, but as a network administrator you should know the important functions of the OSI leader at a high level.
3. TCP/IP vs OSI Model
Let’s now talk about another model that’s similar to the OSI model. It’s called as the TCP/IP model. It’s made up of two protocols as you can see. The first one is TCP, which stands for transmission control protocol, and it runs over IP, the Internet protocol. Together, TCP/IP is the base for the Internet.
Unlike the OSI model that divides network communication into seven layers, the TCP/IP model divides it into four layers. And this was developed by the US Department of Defense (DoD).
This is how the TCP/IP model looks like. We have four layers. The first layer at the bottom is that network access layer. The second layer is the Internet layer. Third, we have the transport layer. And finally, we have the application layer. Let’s compare this to the OSI model.
So, the first two layers of the OSI model, which is the physical and the data link layer, are combined together in the TCP/IP model, which is called as the network access layer. The network layer of the OSI model is called as the Internet layer. The transport layer remains the same. And the last three layers – session, presentation and application layer, are combined into one layer called as the application layer.
The difference is primarily in the structuring of the layers. But from a functionality standpoint, they are pretty much the same. The OSI model is meant to be a reference model, while the TCP/IP model is meant to be an implementation model.
