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These are the user uploaded subtitles that are being translated: 1 00:00:00,000 --> 00:00:04,000 align:middle line:84% What you’ll notice is Spanning Tree convergence is very quick 2 00:00:04,000 --> 00:00:10,000 align:middle line:84% and that’s because we’re running Rapid PVST+ 3 00:00:10,000 --> 00:00:14,000 align:middle line:84% I didn’t make any changes on these switches from the Spanning Tree point of view. 4 00:00:14,000 --> 00:00:22,000 align:middle line:84% So the command sh run | include span shows the default config 5 00:00:22,000 --> 00:00:26,000 align:middle line:84% and notice the Spanning Tree used is Rapid PVST. 6 00:00:26,000 --> 00:00:31,000 align:middle line:84% in the output, it shows us RSTP or Rapid Spanning Tree 7 00:00:31,000 --> 00:00:35,000 align:middle line:84% but this is actually Rapid Per-VLAN Spanning Tree. 8 00:00:35,000 --> 00:00:39,000 align:middle line:84% We can change the mode of spanning Tree 9 00:00:39,000 --> 00:00:42,000 align:middle line:84% but before I do that just to make the point again. 10 00:00:42,000 --> 00:00:48,000 align:middle line:84% at the moment sh spanning-tree on switch 3 11 00:00:48,000 --> 00:00:53,000 align:middle line:84% shows that the root port is gigabit 0/1 this port. 12 00:00:53,000 --> 00:01:02,000 align:middle line:84% If I shut that port down and then type sh spanning-tree again 13 00:01:02,000 --> 00:01:07,000 align:middle line:84% what you’ll notice is gigabit 0/0 is the root port. 14 00:01:07,000 --> 00:01:11,000 align:middle line:84% convergence is very quick with Rapid Spanning Tree 15 00:01:11,000 --> 00:01:13,000 align:middle line:84% because it doesn’t use timers. 16 00:01:13,000 --> 00:01:21,000 align:middle line:84% So the max age and forward delay timers are not used for convergence. 17 00:01:21,000 --> 00:01:23,000 align:middle line:84% The switches send messages to each other 18 00:01:23,000 --> 00:01:27,000 align:middle line:84% with Rapid Spanning Tree to enable quick convergence. 19 00:01:27,000 --> 00:01:34,000 align:middle line:84% So now if we change the Spanning Tree type or mode to PVST 20 00:01:34,000 --> 00:01:38,000 align:middle line:84% we should see that Spanning Tree takes a lot longer to converge. 21 00:01:38,000 --> 00:01:57,000 align:middle line:84% So I’ll change that on all switches; switch 3, switch 4, switch 5. 22 00:01:57,000 --> 00:02:04,000 align:middle line:84% So back on switch 3 sh spanning-tree 23 00:02:04,000 --> 00:02:08,000 align:middle line:84% notice we can see that the switch is still learning 24 00:02:08,000 --> 00:02:10,000 align:middle line:84% which ports are the root port 25 00:02:10,000 --> 00:02:15,000 align:middle line:84% designated port or blocking port, when in the learning state 26 00:02:15,000 --> 00:02:18,000 align:middle line:84% traffic will be block 27 00:02:18,000 --> 00:02:21,000 align:middle line:84% user traffic will only be forwarded 28 00:02:21,000 --> 00:02:23,000 align:middle line:84% when ports transition to the forwarding state. 29 00:02:23,000 --> 00:02:26,000 align:middle line:84% At the moment you can see that the Spanning Tree 30 00:02:26,000 --> 00:02:29,000 align:middle line:84% protocol used are shown here is IEEE 31 00:02:29,000 --> 00:02:32,000 align:middle line:84% but once again you need to be careful 32 00:02:32,000 --> 00:02:36,000 align:middle line:84% because on Cisco switches even though it displays IEEE 33 00:02:36,000 --> 00:02:38,000 align:middle line:84% we're actually using PVST 34 00:02:38,000 --> 00:02:41,000 align:middle line:84% PVST is once again backward compatible 35 00:02:41,000 --> 00:02:45,000 align:middle line:84% so it will be able to talk to an 802.1D switch 36 00:02:45,000 --> 00:02:48,000 align:middle line:84% from another vendor as an example 37 00:02:48,000 --> 00:02:51,000 align:middle line:84% so we can see IEEE in the output here. 38 00:02:51,000 --> 00:02:55,000 align:middle line:84% So once again sh spanning-tree 39 00:02:55,000 --> 00:02:59,000 align:middle line:84% the root port, in this case, is now gigabit 0/0. 40 00:02:59,000 --> 00:03:06,000 align:middle line:84% So what happened because previously we had switch 1 as the root. 41 00:03:06,000 --> 00:03:14,000 align:middle line:84% It still has our command sh spanning-tree 42 00:03:14,000 --> 00:03:18,000 align:middle line:84% shows us that the switch is the root of the topology 43 00:03:18,000 --> 00:03:22,000 align:middle line:84% but gigabit 0/1 is not shown in the output here 44 00:03:22,000 --> 00:03:25,000 align:middle line:84% because I need to no shut that port. 45 00:03:25,000 --> 00:03:29,000 align:middle line:84% So conf t interface g0/1 no shut 46 00:03:29,000 --> 00:03:32,000 align:middle line:84% sh spanning-tree 47 00:03:32,000 --> 00:03:36,000 align:middle line:84% notice that port is a listening port 48 00:03:36,000 --> 00:03:40,000 align:middle line:84% gigabit 0/0 is a blocking port. 49 00:03:40,000 --> 00:03:43,000 align:middle line:84% So this port is blocking, this port is listening 50 00:03:43,000 --> 00:03:50,000 align:middle line:84% and what you’ll notice is it will take it a while to converge 51 00:03:50,000 --> 00:03:52,000 align:middle line:84% I'll put an IP address on this switch 52 00:03:52,000 --> 00:03:56,000 align:middle line:84% I’ll be waiting and then I'll demonstrate this again. 53 00:03:56,000 --> 00:04:14,000 align:middle line:84% Put an IP address on switch 1. 54 00:04:14,000 --> 00:04:17,000 align:middle line:84% I’ll no shut the interface 55 00:04:17,000 --> 00:04:23,000 align:middle line:84% so ping 10.1.1.1 it can ping itself 56 00:04:23,000 --> 00:04:27,000 align:middle line:84% switch 3 no shut the interface 57 00:04:27,000 --> 00:04:34,000 align:middle line:84% Ping 10.1.1.1 ping succeeds so I'll just do that again. 58 00:04:34,000 --> 00:04:37,000 align:middle line:84% Notice the ping from switch 3 to switch 1 succeeds. 59 00:04:37,000 --> 00:04:41,000 align:middle line:84% sh spanning-tree convergence has taken place 60 00:04:41,000 --> 00:04:45,000 align:middle line:84% because gigabit 0/1 is the root port 61 00:04:45,000 --> 00:04:50,000 align:middle line:84% and it's forwarding but now if I shut down gigabit 0/1 62 00:04:50,000 --> 00:04:57,000 align:middle line:84% and then try and ping switch 1, the port has gone down 63 00:04:57,000 --> 00:05:01,000 align:middle line:84% but pings are failing even though we have a redundant link. 64 00:05:01,000 --> 00:05:04,000 align:middle line:84% sh spanning-tree 65 00:05:04,000 --> 00:05:07,000 align:middle line:84% shows me that root port is still learning. 66 00:05:07,000 --> 00:05:16,000 align:middle line:84% Still learning, pings failed, PVST takes a long time to converge 67 00:05:16,000 --> 00:05:20,000 align:middle line:84% and take 30 seconds for that convergence take place. 68 00:05:20,000 --> 00:05:22,000 align:middle line:84% As you can see there, it's just happened 69 00:05:22,000 --> 00:05:24,000 align:middle line:84% sh spanning-tree 70 00:05:24,000 --> 00:05:27,000 align:middle line:84% shows us now that gigabit 0/1 is forwarding. 71 00:05:27,000 --> 00:05:33,000 align:middle line:84% But once again if I no shut gigabit 0/1 72 00:05:33,000 --> 00:05:38,000 align:middle line:84% and did the ping again, the ping would fail 73 00:05:38,000 --> 00:05:41,000 align:middle line:84% because it now needs to learn that this is the better path. 74 00:05:41,000 --> 00:05:43,000 align:middle line:84% sh spanning-tree 75 00:05:43,000 --> 00:05:49,000 align:middle line:84% notice the root port gigabit 0/1 is in the listening state. 76 00:05:49,000 --> 00:05:54,000 align:middle line:84% So we have listening, then we have learning 77 00:05:54,000 --> 00:05:58,000 align:middle line:84% and after while it should go to forwarding 78 00:05:58,000 --> 00:06:00,000 align:middle line:84% but that can take 30 seconds 79 00:06:00,000 --> 00:06:04,000 align:middle line:84% so it’s still learning, now it's gone to forwarding 80 00:06:04,000 --> 00:06:07,000 align:middle line:84% and now pings will succeed. 81 00:06:07,000 --> 00:06:10,000 align:middle line:84% So ports have different states. 82 00:06:10,000 --> 00:06:14,000 align:middle line:84% in a blocking state, user traffic is not forwarded 83 00:06:14,000 --> 00:06:18,000 align:middle line:84% the switch doesn’t learn MAC addresses based on frames received. 84 00:06:18,000 --> 00:06:21,000 align:middle line:84% This is a stable state for a port. 85 00:06:21,000 --> 00:06:25,000 align:middle line:84% A listening and learning port do not forward frames either 86 00:06:25,000 --> 00:06:30,000 align:middle line:84% listening ports don’t learn MAC address based on frames received 87 00:06:30,000 --> 00:06:33,000 align:middle line:84% In other words, they don’t update the MAC address table. 88 00:06:33,000 --> 00:06:36,000 align:middle line:84% A learning port does update the MAC address table. 89 00:06:36,000 --> 00:06:40,000 align:middle line:84% This is a temporary state or transitionary state 90 00:06:40,000 --> 00:06:43,000 align:middle line:84% while the switch has learned the topology. 91 00:06:43,000 --> 00:06:46,000 align:middle line:84% In a forwarding state frames are forwarded 92 00:06:46,000 --> 00:06:50,000 align:middle line:84% MAC addresses are learned and this is a stable state 93 00:06:50,000 --> 00:06:53,000 align:middle line:84% in other words, this is not a transitionary state 94 00:06:53,000 --> 00:06:57,000 align:middle line:84% this state will stay that way until there's change in the topology. 95 00:06:57,000 --> 00:07:01,000 align:middle line:84% A disabled port doesn’t receive6:01 PM 6/21/2017 frames, doesn’t forward frames 96 00:07:01,000 --> 00:07:04,000 align:middle line:84% doesn’t learn about MAC addresses on a port 97 00:07:04,000 --> 00:07:08,000 align:middle line:84% and this port will stand at state until you enable the port. 98 00:07:08,000 --> 00:07:12,000 align:middle line:84% Now if we change that to Rapid Spanning Tree 99 00:07:12,000 --> 00:07:16,000 align:middle line:84% So spanning-tree mode rapid-pvst 100 00:07:16,000 --> 00:07:21,000 align:middle line:84% what we should notice is that convergence takes place a lot quicker. 101 00:07:21,000 --> 00:07:26,000 align:middle line:84% I’ll only enable Rapid Spanning Tree on switch 1, 2 and 3 102 00:07:26,000 --> 00:07:34,000 align:middle line:84% sh spanning-tree rather sh spanning-tree 103 00:07:34,000 --> 00:07:37,000 align:middle line:84% shows us that the Spanning Tree mode now enabled 104 00:07:37,000 --> 00:07:40,000 align:middle line:84% is Rapid Per-VLAN spanning Tree 105 00:07:40,000 --> 00:07:44,000 align:middle line:84% we’ve got a path cost using gigabit 0/1 106 00:07:44,000 --> 00:07:48,000 align:middle line:84% so as you can see gigabit 0/1 is the root port. 107 00:07:48,000 --> 00:07:54,000 align:middle line:84% The switch can ping switch 1 108 00:07:54,000 --> 00:08:02,000 align:middle line:84% I'll shut that port down and when we do a ping again 109 00:08:02,000 --> 00:08:05,000 align:middle line:84% it instantly can ping switch 1 110 00:08:05,000 --> 00:08:09,000 align:middle line:84% even though we’ve just seen the interface go down in the output here 111 00:08:09,000 --> 00:08:15,000 align:middle line:84% because Spanning Tree converge is a lot quicker when using Rapid Spanning Tree. 112 00:08:15,000 --> 00:08:17,000 align:middle line:84% So the moral of the story is that in the real world 113 00:08:17,000 --> 00:08:22,000 align:middle line:84% you wanna use Rapid PVST rather than PVST. 12578