1 00:00:11,410 --> 00:00:13,010 Think about your PC today. 2 00:00:13,150 --> 00:00:17,640 How long does it take your PC to boot up? PCs today 3 00:00:17,660 --> 00:00:25,040 don't take 30 seconds to boot up a lot of them are available within a few seconds or instantly. 4 00:00:25,040 --> 00:00:33,290 That's a problem when we have technology such as spanning tree that take 30 seconds to converge and 5 00:00:33,290 --> 00:00:38,870 forward traffic on a network what I'm gonna do is power cycle the devices 6 00:00:42,440 --> 00:00:50,260 and I'll put the lab into simulation mode notice the switch is now booted up interfaces are showing 7 00:00:50,260 --> 00:00:52,050 orange. 8 00:00:52,200 --> 00:01:01,620 So what happens now is if the PC sends a renew message that DHCP message is gonna be sent to the 9 00:01:01,620 --> 00:01:07,820 switch and then it's gonna be dropped until the ports go to green. 10 00:01:07,820 --> 00:01:16,980 So once the ports go to green the DHCP request message can be forwarded but previously that message 11 00:01:17,040 --> 00:01:23,410 from PC 1 was dropped because the ports were transitioning from listening to learning to forwarding. 12 00:01:23,650 --> 00:01:31,020 So during that period of time DHCP messages will be dropped by the switch. So let's configure spanning 13 00:01:31,030 --> 00:01:35,690 tree PortFast on the switch on which ports do I need to configure it. 14 00:01:36,590 --> 00:01:41,830 I need to configure it on both the client ports and the server port. 15 00:01:41,960 --> 00:01:47,830 We essentially want these three ports in this topology to transition to the forwarding state immediately. 16 00:01:48,560 --> 00:01:54,370 Okay so here's the switch, what I'm gonna do is firstly give the switch a name and then I'm gonna 17 00:01:54,370 --> 00:02:05,430 say interface range gigabit 101 23 those are the three ports in our network that have devices 18 00:02:05,430 --> 00:02:06,910 connected to them. 19 00:02:06,960 --> 00:02:09,000 So I'm gonna say spanning tree 20 00:02:09,000 --> 00:02:11,980 and in this case we're going to select PortFast. 21 00:02:12,090 --> 00:02:14,500 So PortFast, enter 22 00:02:14,730 --> 00:02:20,760 notice we receive a warning message PortFast has been configured on this port. 23 00:02:20,950 --> 00:02:23,400 You can introduce loops if you're not careful. 24 00:02:23,500 --> 00:02:27,720 So use with caution but that's okay for this example. 25 00:02:27,790 --> 00:02:28,940 So show run, 26 00:02:29,170 --> 00:02:33,220 notice we've enabled PortFast on these three ports. 27 00:02:33,220 --> 00:02:39,370 So what I'll do is save the switch configuration and what I'll do now is power cycle the devices 28 00:02:42,020 --> 00:02:47,750 and what we should see is that as soon as the switch boots up the ports go to forwarding which they 29 00:02:47,750 --> 00:02:53,890 have now and my PC can receive an IP address immediately. 30 00:02:53,920 --> 00:03:02,760 So again if I do IP config slash renew the PC receives an IP address immediately the switch transitioned 31 00:03:02,820 --> 00:03:10,920 immediately to the forwarding state on those three ports so spanning tree immediately transitioned to the 32 00:03:10,920 --> 00:03:13,050 forwarding state on those ports. 33 00:03:13,050 --> 00:03:17,660 Let's do that again just to prove the point he has the switch. 34 00:03:17,660 --> 00:03:25,270 It's busy booting up and what you should notice is as soon as it boots up that the ports go green in 35 00:03:25,280 --> 00:03:26,720 Packet Tracer. 36 00:03:26,720 --> 00:03:29,390 There you go show spanning tree, 37 00:03:29,390 --> 00:03:39,120 notice the ports are immediately forwarding and a PC such as PC 1 immediately receives an IP address 38 00:03:40,560 --> 00:03:45,800 because the DHCP messages can be sent to the server immediately. 39 00:03:45,820 --> 00:03:47,090 So there you go, 40 00:03:47,170 --> 00:03:51,110 that's an example of spanning tree PortFast. 41 00:03:51,170 --> 00:03:58,130 So what have you learnt? You've learnt that spanning tree PortFast transitions a Port directly 42 00:03:58,250 --> 00:04:04,690 to the forwarding state instead of transitioning from listening to learning to forwarding with spanning 43 00:04:04,700 --> 00:04:11,250 tree PortFast ports configured as spanning tree PortFast ports immediately transition to forwarding 44 00:04:11,730 --> 00:04:15,780 which means that pieces can get IP addresses from DHB servers. 45 00:04:15,780 --> 00:04:22,680 Users can log in to services such as domain controllers without any delay and the network works more 46 00:04:22,680 --> 00:04:24,030 efficiently. 47 00:04:24,030 --> 00:04:28,770 It's important that you understand what spanning tree PortFAst does for the CCNA exam.