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Networking Fundamentals

1. OSI Model

Welcome back, everybody. Let's begin with the first section, which is Networking Fundamentals. And let's begin with the first topic, which is the OSI Model. The OSI Model is a very fundamental topic in networking. Almost every basic networking course or networking book begins with the OSI model. So let's begin with the OSI Model. 1st. First up, what is the OSI model? It stands for Open Systems Interconnection. In the earliest days of network communication, every vendor or every manufacturer of networking equipment had their own protocol. That means if you purchase devices from two different vendors and try to make them talk, they won't because they do not have a common protocol. So in the 1970s, the International Standards Organization, also known as the ISO, came forward to standardise network communication. The goal was to have a common protocol, irrespective of the underlying architecture, the underlying hardware, or the manufacturer. The OSI model, introduced by ISO, divided network communication into seven layers. It is important to understand that the OSI Model is a purely logical concept. The layers of the OSI model do not directly represent the network components. To remember the layers of the OSI model, there are many mnemonics that are available on the Internet. One of them is very common, and it goes this way: Please do not throw sausage pizza away. The first letter of every word corresponds to the name of the layer. I also found one more on the Internet, and I liked it a lot. It goes this way. People don't need these stupid packets anyway. So it is important. Remember that there is nothing physical about the OSI Model. The application layer does not represent the applications that you're running on the computer, and the physical layer does not represent the physical components of the network as well. Let's now start talking about the different layers. The bottommost layer of the OSI Model is the physical layer. Data at this layer is in the form of bits, which means zeros and ones. The physical layer performs many functions, such as hardware specification. So it defines the electrical and physical specifications of the hardware used to communicate over the network. This includes cables, connectors, frequencies of voltages, and wireless signals. It also defines the type of communication and provides standards for the different types of communication. For example, you have simplex communication, which is communication only in one direction. And to understand this, think about radio broadcasting. The listener is always receiving the signals. He never sends the signals back. The other one is half duplex, which is two-way communication. but you have the limitation that you can only send or receive at any time. You cannot do both at the same time. And to understand that, think of walkie-talkies. You also have full duplex, which allows you to send and receive data at the same time. To understand this, think of a phone call where you can talk and listen at the same time. The physical layer also performs signaling, which means it defines the standards for signal encoding, which is the process of converting digital data (which is zeros and ones) into voltages that can be sent over the wire or the cables. It also specifies network design, which means it provides guidelines regarding the topology and the arrangement of devices. Examples of bus topology, star topology, mesh topology, et cetera.Devices at the physical layer include hubs, repeaters, modems, network interface cards, etc. The second layer of the OSI Model is the Data Link Layer. So we just discussed that data at the physical layer is in the form of bits, which are zeros and ones. When this data moves one level up and reaches the data link layer, it gets transformed into frames. The data link layer is mainly responsible for communication over the same network or over the local area network. It can be divided into two sub layers.The first one is called logical link control, or LLC. This one is responsible for managing the local links between devices communicating on the same network. The second sublayer is called Media Access Control, and it defines methods used to gain access to the shared medium before transmitting data. The data link layer also performs a very important function known as physical addressing. It is also known as the Mac address, and this one is the real address of the device, which is burned onto the chip, which is burned onto the network interface card. We're going to have a separate video about Mac addresses where we'll discuss in detail Mac addresses and how to analyse a Mac address. It also performs flow control, which synchronises the sending and receiving rates of frames. It also provides error control. The protocols that operate at the data link layer include Ethernet, Frame Relay, Token, Ring, Fiber, Distributed Data Interface, etc. The devices that operate at the datalink layer include bridges and layer-two switches. The third layer of the OSI model is the network layer, where the data is in the form of frames at layer two. When they reach layer three, which is the network layer, they get transformed into what is known as "packets." The network layer is responsible for IP addressing. These are logical addresses assigned to devices for routing the packets across different networks. They are also responsible for routing, which is essentially moving the packets across different networks. It also does fragmentation and reassembly, which means if the packets are too large to be sent over the network, it breaks them down into smaller parts known as fragments. The receiving end is then responsible for reassembling all the packets. The protocols that operate at this layer include four IPV), six ICMP, IPsec, etc. And the devices that operate at the network layer include layer three switches, routers, firewalls, etc. The next layer is the transport layer, which is the fourth layer of the OSI model. At the network layer, data is in the form of packets. when it moves one level up. When it reaches the transport layer, it gets transformed into segments. The transport layer is responsible for deciding the transport protocol, which could be TCP or UDP. TCP provides connection-oriented services, which are basically reliable data connections. UDP provides connection-less services, which are useful for real-time data such as voice and video. The transport layer is also responsible for process separation. Think about this: When you have multiple programmes running on your computer at the same time, how does the data reach the right application? Or think about this: When you have multiple browser windows open, the data never gets mixed up. It reaches the right browser window. That's because of process separation using port numbers, and that is a transport layer function. The transport layer also performs segmentation and reassembly, which means if the packet is too large to be sent over the network, it breaks it down into smaller segments, which are then reassembled at the receiving end. And this is done with the help of segment numbers. Some other functions also include flow controls and congestion avoidance. The fifth layer of the OSI Model is the session layer. It is responsible for session management, which means establishing and controlling the session between the sending and the receiving devices. It also performs dialogue control, which means it establishes the communication mode, such as half duplex or full duplex. It also performs synchronization, which is basically the process of avoiding communication errors using sequence numbers. The protocols that operate at the session layer include net bias, socks, network, file system, etc. The 6th layer of the OSI model is the Presentation layer, which is responsible for the presentation of data. It is responsible for presenting or formatting the data, which is received in generic format from the lower layers, into well-known formats. These formats could be JPEG, MPEG, MP4, WaveFormat, etc. It also performs compression to improve data transmission rates, and it also performs encryption to improve data security. Encryption is performed using protocols such as Transport Layer Security, also known as TLS, or Secure Sockets Layer, also known as SSL. The topmost layer of the OSI Model is the Application Layer. Please remember, the application layer does not represent the applications that you're running on the computer. The application layer provides the interface between the applications you run on your computer and the underlying network. It provides the services and the protocols that allow applications to communicate with the network stack. The protocols at the application layer include DNS, HTTP, FTP, etc. Some important tips from this video: first up, remember the names and the order of the layers in the OSI model. Remember the most important functions of every layer. Remember the common protocols at every layer and the devices that operate at every layer. In the next video, we'll start looking at the TCP/IP model, which in some ways is similar to the OSI model, and then we'll compare the OSI model with the TCP/IP model. That's all for this lecture. Let me know if you have any questions. If not, I'd like to thank you for watching and see you at the next lecture.

2. TCP/IP Model vs. OSI Model

Hello and welcome back, folks, to this lecture on the TCP/IP model. In the last lecture, we looked at the OSI model. We understood what the OSI model is and what the different layers of the OSI model are. We also spoke about the functions of the different layers of the OSI model. In this lecture, we'll talk about the TCPIP model, and it's a very short lecture. The TCP IP model has two protocols. The first one is called TCP, also known as Transmission Control Protocol, which runs over IP, also known as the Internet Protocol. The TCP/IP protocol is the base for the Internet. We all use the Internet every day, and the Internet is made up of the TCP/IP Protocol. The TCP/IP model was developed by the US Department of Defense. The TCP/IP model is similar to the USI model, with some minor differences. It divides the network communication into four layers, unlike the OSI model, which divides the network communication into seven layers. The diagram on your screen shows you a comparison between the TCP/IP model and the OSI model. The one on the right hand side is the OSI model, while the one on the left hand side is the TCP/IP model. The first three layers of the OSI model, known as the application layer, the presentation layer, and the session layer, are mapped into one single layer in the TCP/IP model, and it is called the application layer. The transport layer in the OSI model remains the same in the TCP/IP model; it's called the transport layer as well. The network layer in the OSI model is renamed the "Internet layer" in the TCP/IP model. The last two layers of the OSI model, which are the Data Link Layer and the Physical Layer, are mapped into a single layer in the TCP/IP model, and it is called the Network Access Layer. Some important tips from this lecture Remember, the OSI model has seven layers, while the TCP/IP model has four layers. Also, remember the layers of the TCP/IP model. The OSI model is a reference model, while the TCP/IP model is an implementation model. The Internet that we use every day is an example of TCP/IP implementation. The TCP/IP model is built on two protocols, TCP and IP. TCP stands for Transmission Control Protocol, which is a reliable connection-oriented protocol, and it runs over IP, which is the Internet Protocol. In the next lecture, we'll start looking at layer two concepts, specifically Ethernet. We'll understand what Ethernet is, and we'll also talk about the Ethernet frame format. And finally we'll talk about CSM, which stands for Carrier Sense Multiple Access with Collision Detection. So that's it, guys. For this lecture, let me know if you have any questions. If not, I'd like to thank you for watching, and I'll catch you in the next lecture.

3. Ethernet and CSMA/CD

Hello and welcome back to this lecture on Ethernet. In the last lecture, we spoke about the TCP/IP model, and we also compared the TCP/IP model with the OSI model. In this video, we're going to talk about a layer of technology known as Ethernet. First up, what is the ethernet? Ethernet is a suite of technologies and protocols that define communication at layer two, also known as a local area network. Ethernet is not the only technology at layer two. There are other technologies as well, such as token ring FDDI, which stands for "fiber, distributed data interface," etc. Ethernet was first developed by the company called Xerox Corporation, and over time, it became the most popular and widely adopted technology for layer 2 communication. It was later on standardised as IA two three. Now, originally, ethernet was designed to use coaxial cables as a shared medium for communication. This means multiple devices would be connected to the same coaxial medium for communicating over the network. The original standard for ethernet was knownas ten based five, and it supportedspeeds up to ten megabits per second. Now we have fast Ethernet, which supports speeds up to 100 megabits per second. And we also have gigabit ethernet, which is 1000 megabits per second or one gigabit per second. In addition to providing standards for speed, it also provides standards or specifications for the cables, such as coaxial cables and twisted pair cables like Cat 5, Cat 5, E, and Cat 6. It also provides specifications for connectors, like RJ 45. Just in case you've never seen coaxial cables or twisted pair cables, this is what they look like. The one on the left-hand side is coaxial cable. That's what Ethernet was originally designed for. It's no longer used for communication overland, but even today it is used for sending signals for televisions. The one on the right-hand side is the twisted-pair cable, which is what we use these days. Now, let's talk about the Ethernet frame format. So in the video for the OSI model, we discussed that data at layer one or at the physical layer is in the form of zeros and ones. When this data moves one level up, or when it moves to layer 2, it gets transformed into what is known as frames. So when data moves from layer one to layer two, some headers get added onto the data. And that's how the data gets transformed into what is known as "frames." The Ethernet Frame Format looks like what you see on the screen right now. It starts with seven bytes of preamble. Now, the preamble is basically seven bytes of alternating ones and zeroes. Now, I'm sure you must know that one byte is eight bits of data. This one is seven bites, which means it's 56 bits of alternating ones and zeroes, used by the sending and receiving devices to synchronise their internal clocks. After the preamble, we have one byte of SFD, also known as a startframe delimiter. It looks like 101-0101 one.The start frame delimiter signals the end of the preamble and the start of data. It is then followed by six bits of destination Mac address. Now, I know we haven't discussed Mac addresses so far; it is coming up in the next lecture. But just remember that a Mac address is the real address of a computer or the real address of a network device. and it is the address that is burned onto the chip. So, the Ethernet frame format has six bytes of destination Mac address. It's then followed by six bytes of the source Mac address. And then it has two bytes of length. The length field indicates the length of the payload that is about to follow. You then have data, which is the actual payload. The payload must be 46 bytes to 1500 bites in length, followed by the payload. We have a field known as padding. So, if your data is less than the minimum, which is 46 bytes, you add some padding onto it to make sure it has at least 46 bytes of length. And finally, you have FCS. It is also known as the "Frame Check Sequence," and it is four bites in length. It is used for error detection. All right, now let's talk about Csmacd. So, we just discussed that Ethernet was originally designed for communicating over the shared medium, which means multiple devices would be connected to the same wire or the same cable, and they would try to send data over the same medium. Now, Csmacd stands for "Carrier Sends Multiple Access with Collision Detection" when multiple devices try to send data at the same time. Now, since all these devices are connected to the same shared medium, if multiple devices send data at the same time, it would result in a collision. Csmacd is a technology that defines the standards for sending data over a shared medium without resulting in collisions. So this is how it works. Every device that wants to send data must first listen and check for traffic on the shared medium. A device is allowed to transmit only when the shared medium is determined to be free, which means nobody else is transmitting data. Now, if two or more devices transmit data at the same time, it results in what is known as a collision or loss of data. If a collision is detected, sending devices will back off and then wait a random amount of time before they attempt to retransmit the data. All right, so that's about Ethernet and Csmacd. Some important tips from this lecture Remember, Ethernet is a layer-two technology that defines the standards and protocols for communicating over layer two. It is not the only technology at layer two. Other technologies include token ring and FDDI. But over time, Ethernet was found to be very easy to use, and it got adopted as the industry standard. Ethernet defines the standards for speed, the standards for cables, and the standards for connectors Ethernet was originally designed as a protocol for communicating on a shared medium, which was coaxial cables, so there was a need to find a way to transmit data without collision. That's when CSMA CD came in. Csmacd, also known as carrier, sends multiple-access with collision detection, a protocol that is used to send data over a shared medium without resulting in collisions. In the next lecture, we'll start by understanding what a Mac address is. We'll understand the importance of MAC addresses in network communication. We'll understand the structure of a Mac address and the different parts of a Mac address. We'll also talk about the different types of Mac addresses. So that's it, guys, for this lecture. Let me know if you have any questions. If not, I'd like to thank you for watching, and I'll catch you in the next lecture.

4. MAC Addresses

Hello and welcome to this lecture on Mac addresses. In the last lecture, we looked at Ethernet, and we also looked at CSMA/CD. In this lecture, we're going to talk about a layering concept known as Mac addresses. First up, what is a Mac address? Mac addresses are 48-bit addresses that are burned onto the network devices. It is known as the "real address of a device" because it is programmed onto the network chip. It is also known as the physical address of the device. When you think about IP addresses for a second, IP addresses are considered to be logical addresses because you can assign whatever IP addresses you like to your devices. However, the Mac address is programmed into the chip or into the network device. Hence, it is called the "real," or the physical address, of the device. It is an abbreviation for Media Access Control. Let's talk about the Mac address format. I have an example for you on the screen. The example Mac address is one acre, B, four, two, three. The Mac address is represented as six groups of two hexadecimal digits separated by columns. You may already know that hexadecimal captures can range from zero to nine and a two-digit F. And every hexadecimal character, when converted into binary, takes four bits. So we have twelve characters. Twelve times four results in a 48-bit Mac address. The first three groups, or six characters, are together known as the organisational unit identifier, or Oui. It identifies the manufacturer of network equipment. Let's now talk about a broadcast Mac address. a mac address made up entirely of FS So all the twelve characters are only FSis known as a broadcast Mac address. When converted to binary, each F would be represented by 4 once. So when you convert that into binary, you would have a Mac address of only once, or a Mac address of 48 once. When a frame is sent with a destination set as the broadcast Mac address, the frame will reach all the hosts on the same layer of the network. We also have something called multicast Mac addresses. The "Oui" of a multicast Mac address is always set to 10 five E. So we just discussed that every hexadecimal character can be represented by four binary bits. We have six over here, so six times four is 24, so in 01005 we take up the first 24 bits. The 25th bit has to be a zero. As you can see in the diagram, the first 25 bits are indicated in binary format, so you only have the remaining 23 bits to play with. To get the lowest possible multicast Macaddress, we can put in all the zeros. This would result in an address like 1005 E zero. To get the highest possible Mac addresses, we can put all ones in the remaining 23 bits, and that would give us a Mac address like 01005 E, seven FFF. Some important tips for this lecture Remember, the Mac address is a layer-two address, and it is the real address or the physical address of a device because it is programmed or burnt onto the chip. It is 48 bits in length, and it is made up of twelve hexadecimal characters. Hexadecimal characters range from zero to nine and eight F, and every hexadecimal character can be represented by four binary bits. You have twelve characters, so twelve times four is a total of 48 bits. The Mac address representation has six groups of two characters, each separated by columns. The first six characters together are known as the "Oui" or the organisational unit identifier. It identifies the manufacturer of the network equipment. Also, know the difference between broadcast and multicast Mac addresses. In the next lecture, we'll talk about collision domains and broadcast domains, and we'll understand the differences between both of these. So that's it for this lecture. Let me know if you have any questions. If not, I'd like to thank you for watching, and I'll see you in the next lecture.

5. Collision Domains, Broadcast Domains and VLANs

Hello, and welcome back to this video on collision domains, broadcast domains, and VLANs. Let's start by talking about a collision domain. So first up, what is a collision domain? According to one of the definitions, collisions are confined to a physical wireover during which data is broadcast. Because the physical wires are subject to signal collisions, individual land segments are known as collision domains. There's another definition that says a collision domain is the part of the network where packets can collide with one another. My definition is the one that you see at last. Simply put, a collision domain refers to how many devices can send data at the same time. Now, that's how I remember what a collision domain is—how many devices can send data at the same time. So when we talk about collision domains on Ahub, think about a hub for a second. On a hub, there's only one device that can send data at any time. So a hub is one collision domain. When we talk about a switch, every device that's connected to the switch can send data at the same time. So if you have a switch with four ports and four devices connected, that is, four collision domains, When we talk about a router, it's the same. The number of collision domains on a router is equal to the number of devices connected or the number of ports on that router. So you may have a question in the examination that shows you a diagram or that says there are eight devices connected to the switch. How many collision domains do you think the switch has? To remember, on a hub, there's just one collision domain. On a router or on a switch, the number of collision domains is always equal to the number of ports or the number of devices connected. Now let's talk about a broadcast domain on a layer. Two, network broadcasting refers to sending traffic to all nodes on a network layer to broadcast traffic, which stays within a local area network boundary known as the broadcast domain. Another definition says a broadcast domain is a logical division of a computer network in which all nodes can reach each other by broadcast at the data link layer. Simply put, a broadcast domain indicates how far a broadcast can reach on a network. Let's talk about a hub. On a hub, if one device sends a broadcast, every device that is connected to the hub receives the broadcast. So that's one broadcast domain. When we talk about a switch, when one device sends a broadcast, every device connected to that switch receives the broadcast. So it's one broadcast domain. When we talk about a router, it's slightly different. So we have this diagram over here. There's a router in the center, and there are four devices that are connected to the router. When host A sends a broadcast, the broadcast reaches the port on which it is connected, which is fe. Now, routers are designed to drop broadcasts. A router never forwards a broadcast. So when the broadcast reaches port, Fee is going to drop the broadcast. So, that is one broadcast domain. The same applies with Host B. When host B sends a broadcast, when the broadcast reaches port FE 1, the broadcast is going to be dropped. So that's one more broadcast domain. And then host C and host Dare also have their own broadcast domains. So on a router, the number of broadcast domains is equal to the number of ports. Every port is a broadcast domain on its own. This could again be a question on the examination. They might give you a diagram, or they might ask you a question that says there are a couple of devices connected to the router and a couple of devices connected to the switch. Identify the number of broadcast domains. So remember, on a hub and on a switch, it is just one broadcast domain. On a router, the number of broadcast domains is equal to the number of ports or the number of devices connected. All right, so now let's talk about VLANs. First up, why do we need VLANs? A switch is a single broadcast domain, just like we discussed right now. This means when a broadcast is sent, the broadcast is received by every device connected to the switch. Now, this is not a problem when a few devices are connected to the switch. However, as more devices connect to the switch, broadcast starts to become a menace because it can consume network bandwidth. Additionally, you may want to logically separate devices on the same land into different groups. And lastly, you may also want to apply quality of service to different types of traffic. For example, you may want to prioritise voice traffic over normal data traffic. So let's understand what VLANs are. A VLAN or "virtual land" is an alogical separation of devices on the same local area network or on the same switch. It allows you to divide a land segment into multiple logical lands, also known as virtual lands. Important: each VLAN is a separate network with separate layers that we are dressing. And, very importantly, each VLAN is a different broadcast domain. So if you have a switch with the default configuration, it's just one broadcast domain. But if you have a switch that has been divided into multiple VLANs, the number of broadcast domains equals the number of VLANs on that switch. All right? So by default, when you have a switch, it is just one layer three network, right? So in this diagram, I have a switch that just has devices on a single network, which is 192.116. The switch can be divided into multiple networks using VLANs. So on the left hand side you have VLAN one, which is 192-168-1024, and on the right hand side you have Vlad number two, which is 192-168-2024. Notice that both of these are different layer 3 networks. By default, VLANs do not talk to each other; you need to introduce a Layer 3 device to make them talk. For example, if I wanted to make VLAN one and VLAN two talk to each other, I would have to introduce a layer-three device like a router. Routers will be responsible for routing packets between the VLANs. Also remember: VLANs can span multiple switches. So we have a switch on the left that has two VLANs. VLAN One is 192 116.VLAN two is 192.168.0. I can connect switch one to switch two, and I can have my VLAN extend over to switch two. So I can have the same VLAN, which is VLAN one and two, carried over or extended over to switch two. So switch two also has the same VLANs, which are VLAN one and VLAN two. So what happens is that VLAN one on switch one can automatically talk to VLAN one on switch two. But if you wanted to make two different VLANs talk, in that case, you'd have to introduce layer three. Routing some more information By default, VLANs do not talk to each other. A layer-three device such as a router is required to route traffic between VLANs. Different policies can be applied to traffic coming from different VLANs. For example, you can apply a policy that prioritises voice traffic over data traffic. Now the assumption is that voice traffic is on a different VLAN and data traffic is on a different VLAN. When a switch is divided into different VLANs, we need a way to identify or differentiate the VLANs. So each VLAN is identified by a unique 8021QID, which is also known as a tag. VLAN IDs can range from VLAN 0 to VLAN 40, 95. But remember, VLAN IDs 0 and 40 are reserved. They cannot be used for production traffic. The maximum number of VLANs that you can create on a switch depends on the model of the switch. For example, if you have a higher-end switch, it may allow you to create a larger number of VLANs compared to a switch that has a lower model. If you want to know the maximum number of VLANs that are supported, you can use the following configuration mode command. The command goes like this: "Set VLANs," and then you give a VLAN name, and then you give a VLAN ID followed by a question mark. You'll get to know the number of VLANs that are supported on that switch. We are going to try this command when we get to the lapse. For now, you can just make a note of this command. In order to identify packets that belong to a VLAN, Ethernet packets have two fields. So think about this: when I have a switch that has been divided into multiple VLANs, I need a way to know which packet belongs to which VLAN. And to do that, the Ethernet packets or Ethernet frames have two fields that help us identify the VLAN to which the traffic belongs. The first field is known as the Tagprotocol Identifier, or Tpider type field. The second one is the VLAN ID field. When a packet is sent over a VLAN, the TPIDether type field contains the value zero x. The VLAN ID field has the actual ID, or in other words, the actual VLAN ID, which identifies the VLAN to which the packet belongs. Now, if your switch only has the default VLAN, which means no additional VLANs have been configured, packets have the default Azure two-dot, one Q tag. These packets are considered to be untagged. So that's all I wanted to discuss in this lecture. some important tips before we close the lecture. Remember what a collision domain is. Just remember, a collision domain simply refers to how many devices can send data at the same time. We discussed that. On a hub, it's one collision domain. On a switch, it is equal to the number of ports or the number of devices connected on the router. Also, it is equal to the number of ports or the number of devices connected. Remember what a broadcast domain is. It refers to how far the broadcast can reach. On a hub, there is one broadcast domain. On a switch with the default VLAN, there is only one broadcast domain. But then, if you introduce more VLANs, the number of broadcast domains is equal to the number of VLANs. On a router, the number of broadcast domains is equal to the number of ports. Remember what a VLAN is. It allows you to logically divide a switch into multiple networks. Each VLAN is a different Layer 3 network, and it is also a different broadcast domain. By default, VLANs do not talk to each other. We need a layer three device to make them talk. And VLANs are identified by VLAN IDs, also known as 802.1Q IDs or tags. VLAN IDs can range from zero to 4,095, and 4,095 are reserved. It cannot be assigned for production traffic. Also, remember how a VLAN packet is identified on a network using the two fields that we just spoke about. So that's it for this lecture. In the next lecture, we will start by talking about network devices. We'll talk about a repeater. We'll talk about hubs, bridges, switches, and routers. So that's it for this lecture, guys. Let me know if you have any questions. If not, I'd like to thank you for watching, and I'll catch you in the next lecture.

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