1 00:00:00,630 --> 00:00:06,750 At the moment in this topology switch to is the root and we can prove that by using show spanning tree 2 00:00:07,410 --> 00:00:09,000 and notice the local switches. 3 00:00:09,000 --> 00:00:12,420 The root for vlan one in the topology. 4 00:00:13,690 --> 00:00:21,940 No other VLANs have been enabled, so the only ethernet VLAN existing at the moment is VLAN one and 5 00:00:21,940 --> 00:00:25,090 all ports are in VLAN one on all the switches. 6 00:00:25,690 --> 00:00:27,700 When looking at the BPD use. 7 00:00:28,660 --> 00:00:35,770 We can see that the switch is advertising a route path cost of zero and the bridge ID and route identifier 8 00:00:35,770 --> 00:00:36,880 are the same. 9 00:00:37,180 --> 00:00:41,650 On switch one when we capture traffic here. 10 00:00:44,830 --> 00:00:48,550 It's advertising a route path cost of fuel. 11 00:00:48,550 --> 00:00:54,040 And you can see that the bridge identifier is different to the route identifier. 12 00:00:54,610 --> 00:01:05,290 So on switch one, let's change the spanning tree vlan one route so I'll change the switch to become 13 00:01:05,290 --> 00:01:11,890 the route and in this case it'll be the primary route that'll drop the priority of the switch. 14 00:01:12,370 --> 00:01:18,970 Previously, the switch was using a default priority, which we can see in the Wireshark capture. 15 00:01:19,240 --> 00:01:28,630 It was 32768 plus the VLAN number, but now shows spanning three shows us that the switch priority has 16 00:01:28,630 --> 00:01:33,910 been reduced to a value lower than any current route bridge. 17 00:01:34,030 --> 00:01:40,150 So the switch is now become the route of the spanning tree topology bridge, MAC address and root MAC 18 00:01:40,150 --> 00:01:41,290 addresses the same. 19 00:01:41,920 --> 00:01:44,110 So there's our first Wireshark capture. 20 00:01:44,110 --> 00:01:49,840 And if I scrolled down to the latest advertisements, notice the route. 21 00:01:49,840 --> 00:01:51,340 Path cost is zero. 22 00:01:51,580 --> 00:01:55,590 Bridge ID and root identifier are the same. 23 00:01:55,600 --> 00:01:57,640 The priorities have been reduced. 24 00:01:58,350 --> 00:02:02,100 So this switch is the route with a lower priority. 25 00:02:03,510 --> 00:02:07,380 You can see that the bridge property is 24576. 26 00:02:07,530 --> 00:02:15,390 Extended system IDs one because this is VLAN one and the MAC address of the switch is set to the following. 27 00:02:16,000 --> 00:02:22,210 So once again, if we look through the Wireshark capture, this is capture 114 at the moment. 28 00:02:23,030 --> 00:02:27,140 Previously the route identifier and bridge identifier with different. 29 00:02:27,710 --> 00:02:31,610 Now what about switch to previously the switch was the root. 30 00:02:32,270 --> 00:02:34,610 So notice on capture one. 31 00:02:34,940 --> 00:02:39,110 The switch previously had a root path cost of zero. 32 00:02:39,560 --> 00:02:45,800 But scrolling down through the captures, you can now see that it has a root path cost of four. 33 00:02:46,100 --> 00:02:50,330 It's a local bridge identifier has a higher priority. 34 00:02:51,850 --> 00:02:55,330 So the switch is no longer the spanning tree route. 35 00:02:55,780 --> 00:02:57,310 Previously on Switch three. 36 00:02:57,310 --> 00:02:58,630 This was the root port. 37 00:02:59,110 --> 00:03:00,150 So he has the output. 38 00:03:00,160 --> 00:03:05,170 You can see that gigabit zero zero was the route port on switch three. 39 00:03:05,680 --> 00:03:06,870 What is it now? 40 00:03:06,880 --> 00:03:13,030 So show spanning tree notice gigabit zero one is the route port at the moment. 41 00:03:14,350 --> 00:03:14,710 So. 42 00:03:14,710 --> 00:03:16,060 Previously on Switch three. 43 00:03:16,060 --> 00:03:22,570 This was the root port, but the root port is now changed to this port because the switch is now the 44 00:03:22,570 --> 00:03:23,620 spanning tree root. 45 00:03:23,890 --> 00:03:30,670 The path cost using this link is four, whereas now the path cost using this link would be four plus 46 00:03:30,670 --> 00:03:31,090 four. 47 00:03:31,090 --> 00:03:33,700 In other words, eight to get to the root bridge. 48 00:03:36,250 --> 00:03:39,190 Spanning tree topologies can dynamically change. 49 00:03:39,190 --> 00:03:49,870 So as an example, if on switch three are shut down, gigabit is zero one and topped show spanning tree. 50 00:03:50,760 --> 00:03:57,510 What we can see now is that gigabit is zero, zero is now the root port as this port is no longer available. 51 00:03:59,190 --> 00:04:00,240 If I. 52 00:04:00,270 --> 00:04:02,100 No shut that interface. 53 00:04:05,780 --> 00:04:09,440 And top shows spanning tree can see the interface is coming up. 54 00:04:10,360 --> 00:04:17,380 What you can see now is that gigabit zero one has become the root port once again, whereas this port 55 00:04:17,380 --> 00:04:20,920 is now blocking to stop a spanning tree loop.