1 00:00:01,070 --> 00:00:08,780 A number of years ago I had a customer who had a connection from the head office to a data center in 2 00:00:08,780 --> 00:00:15,090 London and they raised a ticket stating that the connection to the datacenter was very slow. 3 00:00:15,320 --> 00:00:21,430 They were connecting to a router with a VPN to the data center and throughput was very poor. 4 00:00:21,470 --> 00:00:26,320 In other words they could ping the data center without any problems. 5 00:00:26,480 --> 00:00:31,570 But when they sent large files the connections were very very slow. 6 00:00:31,580 --> 00:00:38,210 I went to site and on investigation I found that there was a duplex mismatch between a Cisco router 7 00:00:38,360 --> 00:00:44,720 and a Cisco switch duplex mismatches used to cause a lot of problems in the past. 8 00:00:44,720 --> 00:00:49,060 The negotiation of Duplaix often failed on 10 one hundred links. 9 00:00:49,340 --> 00:00:56,330 And in those days it was recommended that you hard code speed and duplex on links between devices such 10 00:00:56,330 --> 00:01:02,990 as Cisco routers and switches today fortunately things are a lot better today it's generally recommended 11 00:01:03,110 --> 00:01:09,650 that you allow switches and routers to use auto negotiation of duplex as well as speed. 12 00:01:09,650 --> 00:01:15,260 Now in some cases you may want to hard code at the speed and duplex between your switches and your routers 13 00:01:15,800 --> 00:01:23,110 but be aware that if you configure it incorrectly you may end up with an issue such as the following. 14 00:01:23,120 --> 00:01:26,990 Notice the switch is stating that there is a duplex mismatch on fossa. 15 00:01:26,990 --> 00:01:32,560 Ethan it is 0 4 to another switch on Fosset Ethernet 0 4 on the router. 16 00:01:32,570 --> 00:01:38,480 We have a duplex mismatch on FASA Ethan and 0 to the switch on fossa. 17 00:01:38,480 --> 00:01:41,330 Ethan it is 0 3 in this video. 18 00:01:41,330 --> 00:01:47,390 I'm not using Jeana's 3 I'm using physical switches and I'm simply using genius 3 to show you what the 19 00:01:47,390 --> 00:01:49,360 topology looks like. 20 00:01:49,370 --> 00:01:57,020 I have two routers each in turn connected to 29 50 switches which are connected to 750 switches and 21 00:01:57,020 --> 00:02:04,150 I have a laptop connected on port 0 5 to the first 30 750 switch. 22 00:02:04,190 --> 00:02:08,220 So let's have a look at some of the issues you may encounter with Duplaix mismatches. 23 00:02:08,270 --> 00:02:12,820 Remember that with full duplex a device can transmit and receive at the same time. 24 00:02:13,040 --> 00:02:19,910 Whereas with half duplex only one side can send in other words a device cannot send and receive simultaneously 25 00:02:20,360 --> 00:02:25,040 with half duplex one party transmits and one party receives with full duplex. 26 00:02:25,040 --> 00:02:30,710 Both parties can transmit and receive at the same time half duplex was required for connections to hubs 27 00:02:31,220 --> 00:02:34,080 these days because of the use of Ethan switches. 28 00:02:34,130 --> 00:02:40,670 We generally want to use full duplex which means as an example on this 100 megabits per second link 29 00:02:41,090 --> 00:02:46,040 the switch can send traffic to the course which at 100 megabits per second and at the same time the 30 00:02:46,040 --> 00:02:51,820 cost switch can send traffic to the 29 50 switch at 100 megabits per second. 31 00:02:51,830 --> 00:02:59,000 So we actually have a throughput in theory of 200 megabits per second 100 in each direction when using 32 00:02:59,000 --> 00:03:07,470 full duplex now cabled the link here to show you a problem with Duplaix between two 29 fifties. 33 00:03:07,640 --> 00:03:13,950 And I'll also demonstrate Orta negotiation of speed and duplex between thirty seven fifties and 29 50s 34 00:03:14,510 --> 00:03:17,330 as well as a PC and a switch. 35 00:03:17,330 --> 00:03:22,760 But before we do that let's have a look at some of the problems you may encounter when you have a duplex 36 00:03:22,760 --> 00:03:23,560 mismatch. 37 00:03:23,750 --> 00:03:26,800 As mentioned your throughput may be a problem.