1 00:00:00,000 --> 00:00:05,000 In this video, I’m gonna show you how data flows through devices in a network. 2 00:00:05,000 --> 00:00:11,000 So how does data flow for example, through a hub or a switch or router? 3 00:00:11,000 --> 00:00:15,000 Is the flooded out of all ports or is it only send out of an individual port? 4 00:00:15,000 --> 00:00:21,000 And when I talk about data, I’m implying that on a switch a frame is forwarded out 5 00:00:21,000 --> 00:00:28,000 of a port and on a router I’m talking about a packet is forwarded out of a port. 6 00:00:28,000 --> 00:00:31,000 So in networking, it’s important to understand those terms and it’s also very 7 00:00:31,000 --> 00:00:36,000 important to understand how traffic flows through devices in the network. 8 00:00:36,000 --> 00:00:39,000 If you have a router where does the traffic go? 9 00:00:39,000 --> 00:00:42,000 If you have switch, out of which port does the traffic go? 10 00:00:42,000 --> 00:00:44,000 So let’s look at how data flows in a network. 11 00:00:44,000 --> 00:00:48,000 We firstly gonna start off with an introduction to the different types 12 00:00:48,000 --> 00:00:51,000 of communication that takes place in the data network. 13 00:00:51,000 --> 00:00:57,000 We gonna look at unicast traffic vs. multicast traffic vs. broadcast traffic. 14 00:00:57,000 --> 00:01:02,000 I’m then gonna explain the term CSMA/CD which means 15 00:01:02,000 --> 00:01:06,000 Carrier Sense Multiple Access Collision Detection 16 00:01:06,000 --> 00:01:08,000 I’m then gonna spend quite a bit of time 17 00:01:08,000 --> 00:01:12,000 looking at the differences between hubs bridges, switches and routers. 18 00:01:12,000 --> 00:01:16,000 And I’m gonna show you how packet flows through those different devices. 19 00:01:16,000 --> 00:01:20,000 I’ll be referring to the OSI model throughout this video. 20 00:01:20,000 --> 00:01:25,000 I’m assuming at this point that you understand what the OSI model is 21 00:01:25,000 --> 00:01:28,000 and the different layers of the OSI model. 22 00:01:28,000 --> 00:01:32,000 If you’re unsure review the OSI video that’s part of this course. 23 00:01:32,000 --> 00:01:36,000 So in this video I’m not gonna give you the details of where a device 24 00:01:36,000 --> 00:01:39,000 in the OSI model resides, I’m gonna refer to terms 25 00:01:39,000 --> 00:01:43,000 such as a router is a layer 3 device, a switch is a layer 2 device. 26 00:01:43,000 --> 00:01:47,000 If you aren't sure about what that means please review the OSI video. 27 00:01:47,000 --> 00:01:51,000 So let’s start off with the basic types of communication 28 00:01:51,000 --> 00:01:53,000 that you'll encounter in the data network. 29 00:01:53,000 --> 00:01:57,000 This is one of those fundamental building blocks that you need to understand. 30 00:01:57,000 --> 00:02:01,000 So the first type of communication is unicast. 31 00:02:01,000 --> 00:02:05,000 Unicast is essentially where one device speaks to one other device. 32 00:02:05,000 --> 00:02:12,000 It's one to one communication, in other words, device A is communicating with device B 33 00:02:12,000 --> 00:02:17,000 the second type of communication is a broadcast, a broadcast is where one device 34 00:02:17,000 --> 00:02:23,000 sends traffic to all devices in the same subnet or in the entire network. 35 00:02:23,000 --> 00:02:27,000 There are different types of broadcast and we'll talk about some of them later. 36 00:02:27,000 --> 00:02:33,000 But as an example a broadcast to the local subnet means that all devices 37 00:02:33,000 --> 00:02:38,000 in the same subnet have the broadcasting device receive the broadcast. 38 00:02:38,000 --> 00:02:43,000 A broadcast to all hosts or networks means that the broadcast 39 00:02:43,000 --> 00:02:45,000 goes everywhere in the entire network. 40 00:02:45,000 --> 00:02:50,000 However in a lot of real world implementation, broadcast are limited 41 00:02:50,000 --> 00:02:55,000 and blocked by layer 3 devices such as switches and routers. 42 00:02:55,000 --> 00:02:59,000 So a broadcast would typically not go everyway in a network. 43 00:02:59,000 --> 00:03:03,000 Broadcast can cause a lot of problems and are therefore contained or limited 44 00:03:03,000 --> 00:03:08,000 in data networks, but essentially the idea of a broadcast is that all devices 45 00:03:08,000 --> 00:03:16,000 on the local segment or local subnet will receive the broadcast sent by single device. 46 00:03:16,000 --> 00:03:21,000 Now broadcast can be useful as an example if 2 windows machines 47 00:03:21,000 --> 00:03:27,000 are configured with the same name, you'll receive a warning about that because 48 00:03:27,000 --> 00:03:30,000 a broadcast is sent by those devices on the local network. 49 00:03:30,000 --> 00:03:35,000 That’s how the devices learned about each other and realized that multiple 50 00:03:35,000 --> 00:03:40,000 devices have the same name. So broadcast do have the uses but do cause a lot of 51 00:03:40,000 --> 00:03:47,000 problems in IPv4 networks and therefore in IPv6 broadcast support has been removed. 52 00:03:47,000 --> 00:03:54,000 In an IPv6 network broadcast are not supported. Now, what about multicast? 53 00:03:54,000 --> 00:03:59,000 Multicast have some of the advantages of broadcast, in that a single device 54 00:03:59,000 --> 00:04:03,000 can speak to many devices but it gets rid of some of the issue related to broadcast. 55 00:04:03,000 --> 00:04:09,000 Broadcast send traffic to people that don’t necessarily want the traffic 56 00:04:09,000 --> 00:04:16,000 where as with the multicast only devices that subscribe to the multicast receive it. 57 00:04:16,000 --> 00:04:21,000 So devices have to explicitly ask for multicast traffic before they receive it. 58 00:04:21,000 --> 00:04:25,000 So they won’t receive the multicast if they for example 59 00:04:25,000 --> 00:04:28,000 unsubscribe from that multicast. 60 00:04:28,000 --> 00:04:35,000 So to use some analogies, a broadcast is like a spammer were sending mail or email 61 00:04:35,000 --> 00:04:39,000 or traffic to everyone even to people who don’t want it. 62 00:04:39,000 --> 00:04:45,000 A multicast on the other hand is kind of a like an opt in or subscription service 63 00:04:45,000 --> 00:04:52,000 to a mailing list, so you may subscribe to an email mailing system giving information 64 00:04:52,000 --> 00:04:58,000 about Cisco CCNA, you can always opt out of that mailing list which means 65 00:04:58,000 --> 00:05:02,000 you no longer receive the emails, well in theory at least. 66 00:05:02,000 --> 00:05:05,000 So the idea with the broadcast is you will receive the traffic 67 00:05:05,000 --> 00:05:07,000 even though you don’t want it. 68 00:05:07,000 --> 00:05:12,000 The idea with the multicast is you can optionally receive the traffic or 69 00:05:12,000 --> 00:05:15,000 optionally opt out of receiving the traffic. 70 00:05:15,000 --> 00:05:20,000 Now another analogy which is useful in a classroom base environment is 71 00:05:20,000 --> 00:05:25,000 if I were standing at the front of the class as an instructor I would be talking 72 00:05:25,000 --> 00:05:30,000 and everyone in the class would be listening to what I’m saying, that’s a broadcast. 73 00:05:30,000 --> 00:05:33,000 So typically that happens in the morning when the class first starts. 74 00:05:33,000 --> 00:05:39,000 I’m speaking everyone in the room is listening, however typically especially 75 00:05:39,000 --> 00:05:44,000 after lunch an example, the classroom turns into a multicast where some people 76 00:05:44,000 --> 00:05:48,000 have unsubscribe from what I’m saying and that maybe happening right now 77 00:05:48,000 --> 00:05:51,000 which is unfortunate but hopefully not. 78 00:05:51,000 --> 00:05:55,000 Hopefully you're still listening, so I might be speaking in front of a class of 10 79 00:05:55,000 --> 00:05:59,000 people but only 5 of those people are listening to what I’m saying 80 00:05:59,000 --> 00:06:03,000 The other 5 people have unsubscribed from what I’m saying 81 00:06:03,000 --> 00:06:08,000 and are no longer listening to me. That’s an example of a multicast. 82 00:06:08,000 --> 00:06:12,000 so I’m hoping that this video won’t turn into 83 00:06:12,000 --> 00:06:17,000 multicast where you unsubscribe from what I’m saying.