hey I'm Rob Witcher from destination certification and I'm here to help you pass the cissp exam we're going to go through a review of the major topics related to The OSI model in domain 4 to understand how they interrelate and to guide your studies this is the first of four videos for domain 4 I've included links to the other mindmap videos in the description below these mind maps are one part of our complete cisp Master [Music] Class ah domain four Communications and network security the domain that gives most people a headache when preparing for the cisp exam you certainly don't need to be a networking expert to pass the exam but you do need to understand some fundamentals and this makes sense our modern-day systems are vastly interconnected through a spider's web of different networking Technologies if we ever hope to secure our systems as Security Professionals then it's important for us to understand the fundamentals of networking let's dive in shall we we're to begin our Whirlwind review of domain 4 with the OSI model the open systems interconnection model the first very important thing to understand about the OSI model is that it is a model a guide a conceptual framework which is meant to help you understand how systems should communicate with each other the key wordss in that last sentence are guide and concept Abal framework the OSI model is a suggestion it is not a strict set of rules that must be precisely complied with that's why this is a highly simplified diagram of a few of the most common protocols and how they map to the seven layers of the OSI model as you can see there are many protocols that operate at multiple layers of the OSI model and blur the lines between layers to say This is complicated is a massive understatement and you certainly don't need to understand all of these protocols to this depth of detail I I do want to highlight a very important point though when you read different books about protocols or Google a protocol you will quickly find conflicting answers as to which OSI layer a protocol operates at a perfect example is ARP the address resolution protocol is used to translate an IP address which operates at layer three of the OSI model down to a MAC address which operates at Layer Two the data link layer of the OSI model so at which layer of the OSI model does the ARP protocol operate both layers two and three here's why I'm telling you this you will see questions on the exam asking you which layer a specific protocol or device operates at in the OSI model and I'm going to give you some nice simple answers but recognize that this gets super complicated real fast if you dig into it and you will find many conflicting answers out there all right the seventh layers of the OSI model you need to memorize the seven layers and they are one physical two data link three Network four transport five session six presentation and seven application and here are a couple of pneumatics to help you memorize them starting at the bottom we have the classic please do not throw sausage pizza away or starting from the top we have all people seem to need data processing I know some spicier ones but I'm not going to share them here on YouTube as they might object okay now that introduction out of the way let's go through each layer and I'm going to start at the bottom with layer one and briefly explain what is supposed to happen at each layer and the major protocols devices and other interesting tidbits at each layer layer one the physical layer is where the binary transmission of data across physical media occurs electrons across wires photons through fiberoptic cables and electromagnetic waves through the air for wireless all different way of moving bits how specifically do we move the bits there are two major methods with wires of some sort or wirelessly through the air the types of wire you need to know a we bit about include twisted pair also known as ethernet cable a category 5 or more commonly Cat 5 cable and there are newer standards like cat 6 cat 7 and Cat 8 cable and they all use the venerable RJ45 Jack there's also coao and fiber optic cable from a wireless perspective there are three major ways we can send bits wirelessly that you should know abouto radio frequency which includes Wi-Fi infrared and microwave from a wireless perspective there are three major ways we can send bits wirelessly that you should know about radio frequency which includes Wi-Fi infrared and microwave microwave is a good way to connect buildings that are within line of sight and you want to save the cost of burying Cable in the ground now let's talk about how we interconnect several systems together there are different ways we can connect the wires to create different topologies the vast majority of the networks that we use today are fundamentally bus topologies every system is connected to every other system across a wire this is a broadcast technology and the major issue here is collisions if two systems try and send data across the bus at the same time you will have a collision and the more systems the more collisions this is a major problem this brings us to tree topology which is still fundamentally a bust topology but we are beginning to segment the network to force signals to go down a particular branch which helps to reduce collisions star topology means all the systems are interconnected through a central device like a switch the big advantage of having a switch in the middle here is the switch can have some intelligence and only direct packets to the intended recipients which is a huge help in reducing collisions and increasing Network throughput mesh topology means every device is interconnected with every other device this is wonderful for redundancy full mesh networks are very rare but partial mesh networks where critical devices are interconnected like boundary firewalls and routers are very common and the final topology we'll cover here is the old school token ring token ring has the big advantage of built-in collision avoidance a token is passed around the ring and a system can only send data when it has the token meaning only one system can send data at a time no collisions but if a system malfunctions and doesn't pass on the token on the ring no one gets to talk that's one reason token rings are pretty rare these days as I mentioned the vast majority of network works that we use today are fundamentally bust topology which has the big problem of collisions we therefore need methods of effectively dealing with collisions csma CA carrier sense multiple access with Collision of voidance as the name implies avoids collisions and is used primarily in wireless networks csmac CD carrier sense multiple access with Collision detection on the other hand detects if a collision has occurred and deals with it csmac CD is used primarily in wired networks the major devices you should know about that operate at the physical layer are hubs repeaters and concentrators these devices have essentially no intelligence they just repeat signals but they do it incredibly quickly and efficiently this is a common theme we will see here in the OSI model at the lowest level of the OSI model the physical layer there is essenti zero intelligence zero ability to make decisions but wicked good speed as we move up we gain more intelligence at each layer at the cost of efficiency the major protocol you should know about a layer one is 802. 11 which is a whole family of protocols for wireless local area networks you've no doubt heard about protocols such as 802. 11a 802.
11b g n AC and perhaps the upcoming 8 Wi-Fi 6 802. 11a he needs to know a bit about a few of these 80211 protocols which I'll cover in the next mind map let's now move on up to Layer Two the data link layer which is responsible for physical addressing and reliable point-to-point connections is it Layer Two that we have the very important Mac media Access Control address Mac addresses are a unique identifier assigned to every network interface controller ever manufactured every device that it connects to a network has one of these unique Mac addresses layer 2 switches use Mac addresses to figure out which system to send data to Layer Two devices you should know about are switches and Bridges bridges connect two physical Network segments together and switches interconnect multiple devices so they can talk to each other and switches intelligently only forward data to an intended recipient based on Mac address greatly improving Network performance over hubs there are newer more intelligent switches that operate at layer 2 and layer 3 however unless specifically stated you should assume a switch operates at layer 2 and the layer 2 protocols 802. 11 802.
1x which is used for authenticating network devices to a network it is a protocol used for network access control ARP address resolution protocol which as I mentioned in the intro translates an IP address down to a MAC address it's worth mentioning there is also RAR reverse address resolution protocol which as you can probably guess translates a MAC address up to an IP address pptp point2 Point tunneling protocol is used for creating tunnels lots more on tunnels and bpn in video four of domain 4 PPP pointto Point protocol which encapsulates Internet Protocol IP traffic so that it can be transmitted over an analog connections and provides authentication encryption and compression and authentication protocols Pap Chap and EAP which I'll talk about in more detail in the next video next layer up is layer three the network layer and it is responsible for logical addressing routing and delivery of datagrams and it is at layer three that we have the crucially important Internet Protocol IP addresses IP addresses are much like your postal address if anyone wants to mail you a letter from somewhere in the planet then they need your postal address your country Province or state date City street and house number so that a letter can be routed to your specific mailbox IP addresses serve the same function on networks they identify a specific system and allow datagrams packets to be roted to the system across local networks and even across the vast inter tubes lots more on IP addresses in the next video layer three devices you should know about routers and packet filtering firewalls routers forward packets between different Network segments based on IP addresses and packet filtering firewalls are the simplest and fastest firewalls I'll talk a lot more about firewalls in video three of domain 4 and the layer three protocols you should know about icmp internet control message protocol allows network devices to send error and control messages and enables the Ping and trace route utilities IP SEC Internet Protocol security is the bewildering Suite of protocols that provide data Authentication integrity and confidentiality I'll talk about the components of IPC in video 4 and igmp internet group management protocol which is used by hosts and adjacent routers to establish multicast group memberships igmp enables multicast groups the ability to transmit the same packets to multiple systems at once moving on up we have layer four the transport layer which is responsible for endtoend connections with error correction and detection is at layer four that we have ports different ports equate to different services that are offered by a system across a network you can kind of think of ports as the doors in a building if a port is open if a door is open to a room then you can access the services of that room a door might be open to a cafeteria or a washroom or a bedroom there are 65,535 ports and I would recommend that you memorize all of them and when what they're used for not funny okay just remember a few of the most common ports Port 21 is FTP file transfer protocol used to transfer files between a client and a server Port 22 is SSH secure shell used to remotely connect to a system Port 23 is telnet a remote command line protocol Port 53 is DNS the domain name system protocol which translates domain names to IP addresses so we can remember nice simple domain names like google. com and not have to remember 14225 1.
