1 00:00:01,150 --> 00:00:09,160 Now, unlike FedEx or DHL, we're not sending physical packages between network devices. 2 00:00:09,160 --> 00:00:10,540 We're sending packets. 3 00:00:10,840 --> 00:00:17,530 So how does a phone indicate to a switch that its traffic is of great importance? 4 00:00:17,740 --> 00:00:23,350 And how does one switch indicate to another switch that some packets are more important than others? 5 00:00:23,890 --> 00:00:31,180 So this is called classification and marking a phone would classify its own traffic as being important, 6 00:00:31,180 --> 00:00:36,190 but the traffic from a PC would be classified as not being important. 7 00:00:36,370 --> 00:00:42,700 A switch can be configured with access lists, or it could use other technologies such as end bar or 8 00:00:42,700 --> 00:00:51,010 network based application recognition to recognize certain applications such as HTTP or voice traffic 9 00:00:51,010 --> 00:00:54,910 or video traffic, and then tries the traffic accordingly. 10 00:00:55,120 --> 00:01:01,930 So essentially a phone sees its own traffic as important, but not the traffic of a PC. 11 00:01:02,250 --> 00:01:08,860 The switch or a router has many options that you can use to put traffic into classes. 12 00:01:09,490 --> 00:01:16,000 Again, you could use an access list or network based application recognition, but once you've put 13 00:01:16,000 --> 00:01:21,190 your traffic into a class, so as an example, the phone says it's traffic is important, it's voice 14 00:01:21,190 --> 00:01:21,910 traffic. 15 00:01:22,120 --> 00:01:26,620 It needs to mark the traffic and send it to the first switch. 16 00:01:26,650 --> 00:01:31,660 So all packets sent from the phone to the switch need to be marked as important. 17 00:01:31,840 --> 00:01:35,860 Now that can be done at a layer two using a 2 to 1 queue. 18 00:01:36,100 --> 00:01:40,270 So on Ethernet, we would require a to two one queue links. 19 00:01:40,270 --> 00:01:46,630 And in the attitude of one queue header, we can change what's called the cost field or class of service 20 00:01:46,630 --> 00:01:54,790 field to indicate the importance of the traffic that is known as ADA 2 to 1, P or ADA two or one priority 21 00:01:54,790 --> 00:01:55,450 bits. 22 00:01:55,750 --> 00:02:02,830 We could also use MPLS experimental bits to indicate that the traffic is important at a layer three. 23 00:02:02,830 --> 00:02:10,449 In the IP header, we've got IP precedence and differentiated services code points or DHCP IP explicit 24 00:02:10,449 --> 00:02:16,000 congestion notification or ECN can also be used, but that's not covered in the Q&A course. 25 00:02:16,770 --> 00:02:21,600 The Layer two and layer three parameters are the ones that you should concentrate on for the CCNA exam. 26 00:02:22,050 --> 00:02:28,260 So at layer two, we have added 2 to 1 Q or eight or 2 to 1 PPI class of service bits. 27 00:02:28,440 --> 00:02:35,160 There are three bits in the header which equated to eight classes of service in the range of 0 to 7. 28 00:02:35,640 --> 00:02:37,380 So let's look at that practically. 29 00:02:37,560 --> 00:02:42,780 I'm going to capture traffic on this link between the phone and the switch. 30 00:02:46,130 --> 00:02:48,050 So why shock is capturing traffic? 31 00:02:52,300 --> 00:02:57,520 Now this phone icon is actually an osteo, not a node, which is a package generator. 32 00:03:00,230 --> 00:03:08,120 In the packet generator, I can specify the priority bits of an 801 Q header. 33 00:03:08,390 --> 00:03:15,350 Notice the values are from 0 to 7 because this is a phone, I'm going to set the priority to five. 34 00:03:16,350 --> 00:03:16,620 Click. 35 00:03:16,620 --> 00:03:19,840 Okay, and then I'm going to start generating packets. 36 00:03:19,840 --> 00:03:22,080 So packets are being sent into the network. 37 00:03:22,260 --> 00:03:24,870 These are UDP packets that I'm sending. 38 00:03:25,590 --> 00:03:26,550 So. 39 00:03:28,110 --> 00:03:30,780 Here's one of the packets that have been generated. 40 00:03:32,510 --> 00:03:33,920 And notice that ethernet too. 41 00:03:33,950 --> 00:03:36,890 We have a source and destination mac address. 42 00:03:37,310 --> 00:03:45,290 We are generating an 8 to 1 Q frame and in the editor to one Q frame notice we've got a priority field. 43 00:03:45,410 --> 00:03:54,880 So the priority field or COS field consists of three binary bits in the range 000 up to 111. 44 00:03:54,890 --> 00:04:01,460 In other words, in the range of 0 to 7, there are eight binary values that we can configure. 45 00:04:01,460 --> 00:04:06,800 And in this case I've set the value to five to indicate voice traffic. 46 00:04:06,800 --> 00:04:08,540 So back in ostinato. 47 00:04:09,020 --> 00:04:12,860 I'll change the cost value to seven. 48 00:04:14,300 --> 00:04:16,459 And what I'll do is generate more frames. 49 00:04:16,970 --> 00:04:25,880 So scrolling down to the latest frames, notice the party bit is three binary ones, which equates to 50 00:04:25,880 --> 00:04:27,080 network control. 51 00:04:27,080 --> 00:04:30,290 In this case, I'll filter for UDP. 52 00:04:31,460 --> 00:04:34,550 In the previous frame, it showed up as video. 53 00:04:34,700 --> 00:04:37,730 In other words, we require low latency and jitter. 54 00:04:37,940 --> 00:04:43,370 Now, that's used by Cisco phones to indicate important voice traffic. 55 00:04:44,210 --> 00:04:51,320 This R&D guide has some recommendations for what you should mark traffic as so at a layer two costs 56 00:04:51,320 --> 00:04:53,300 or MPLS experimental bits. 57 00:04:53,780 --> 00:04:58,160 A cost of five is what you used for voice video. 58 00:04:58,170 --> 00:05:00,770 Cisco recommend using a cost value of four. 59 00:05:01,520 --> 00:05:04,370 Mission critical data should have a cost value of three. 60 00:05:04,610 --> 00:05:08,360 Call signaling to set up telephone calls should have a cost value of three. 61 00:05:08,930 --> 00:05:13,280 And then it goes all the way down to best effort, which has a cost value of zero. 62 00:05:14,030 --> 00:05:22,760 So as an example, if we were sending call signaling something like CIP or H to three, the cost value 63 00:05:22,760 --> 00:05:24,200 should be set to three. 64 00:05:24,740 --> 00:05:27,230 So we should set the cost value here to three. 65 00:05:29,400 --> 00:05:32,070 And you can generate some frames. 66 00:05:32,490 --> 00:05:36,390 I notice over here the cost value is set to three. 67 00:05:36,720 --> 00:05:39,780 Binary is 011 decimal is three. 68 00:05:40,020 --> 00:05:45,450 Now applications should follow the conventions, but sometimes they don't. 69 00:05:45,660 --> 00:05:48,330 And this is where the trust boundary is important. 70 00:05:48,900 --> 00:05:54,270 Would you trust your users to set their quality of service correctly? 71 00:05:54,270 --> 00:05:55,590 Typically not. 72 00:05:56,260 --> 00:06:01,960 So in this case, the switch can trust the markings that it receives from the phone, but not necessarily 73 00:06:01,960 --> 00:06:04,780 the markings that are received from this PC. 74 00:06:04,990 --> 00:06:07,410 So again, they are different ways to mock. 75 00:06:07,420 --> 00:06:12,520 We can market layer two in Ethernet frames using an edited or one Q header. 76 00:06:12,670 --> 00:06:17,950 As I've demonstrated, there were eight classes in the range 0 to 7. 77 00:06:18,310 --> 00:06:22,780 We can also mock type of service, which is at layer three. 78 00:06:24,120 --> 00:06:26,160 So in the type of service header. 79 00:06:27,460 --> 00:06:33,370 There are eight binary bits and in the old days we used to have what was called IP precedence, which 80 00:06:33,370 --> 00:06:36,190 marked the most significant three bits. 81 00:06:36,490 --> 00:06:43,180 Today we use a differentiated service code points or server bits, which is a marking of the most significant 82 00:06:43,180 --> 00:06:44,080 six bits. 83 00:06:44,590 --> 00:06:46,450 I'll talk about this in more detail in a moment. 84 00:06:46,900 --> 00:06:52,840 But just to demonstrate it, what we could do is under the IP header. 85 00:06:53,480 --> 00:06:57,500 We can set a type of service or DHCP value. 86 00:06:59,070 --> 00:07:01,890 So if we send a frame into the network. 87 00:07:02,930 --> 00:07:10,610 Notice at layer two, we have the editor to one Q header set to a cost value of three, but at least 88 00:07:10,610 --> 00:07:11,390 three. 89 00:07:11,720 --> 00:07:20,000 We have a differentiated service code point set in this example to expedited forwarding or 46. 90 00:07:20,000 --> 00:07:28,370 So we've marked one, two, three, four, five, six bits in the IP header, explicit condition notification. 91 00:07:28,430 --> 00:07:34,010 The last two bits here are not used and you don't need to know ECN for the CCNA exam. 92 00:07:34,490 --> 00:07:41,090 But notice the type of service field in the IP four header is eight bits in size. 93 00:07:41,570 --> 00:07:47,510 IP precedence uses the most significant three bits differentiated services code points uses the most 94 00:07:47,510 --> 00:07:49,280 significant six bits. 95 00:07:49,430 --> 00:07:52,700 ECN uses the least significant two bits. 96 00:07:53,610 --> 00:07:55,260 And that's what we can see here. 97 00:07:55,290 --> 00:07:59,550 Here's an example of DHCP and ECN. 98 00:08:00,150 --> 00:08:02,490 Notice this is just a standard IP packet. 99 00:08:02,490 --> 00:08:05,640 We have source address, destination address. 100 00:08:05,940 --> 00:08:08,340 We have the protocol being UDP. 101 00:08:08,520 --> 00:08:17,040 But one of the fields is the toss field or type of service field which consists of DHCP and ECN today.