1 00:00:00,000 --> 00:00:09,000 So on switch 1 the only port that’s forwarding is gigabit 0/0 as shown here. 2 00:00:09,000 --> 00:00:12,000 Other ports on the switch are blocking. 3 00:00:12,000 --> 00:00:16,000 So taking a picture of the topology 4 00:00:16,000 --> 00:00:21,000 this port is blocking, this port is blocking and this port is blocking. 5 00:00:21,000 --> 00:00:28,000 The only port that is forwarding is gigabit 0/0 and we can see that in the output here. 6 00:00:28,000 --> 00:00:32,000 So gigabit 0/0 is a root port. 7 00:00:32,000 --> 00:00:36,000 So we could say this is the root port of that switch. 8 00:00:36,000 --> 00:00:39,000 Other ports are blocking. 9 00:00:39,000 --> 00:00:41,000 Now what about switch 2? 10 00:00:41,000 --> 00:00:47,000 So on switch 2 for VLAN 10 all ports are forwarding 11 00:00:47,000 --> 00:00:51,000 because this is the root bridge. 12 00:00:51,000 --> 00:00:53,000 On a root bridge, all ports are in the forwarding state 13 00:00:53,000 --> 00:00:57,000 you can't get closer to the root bridge than the root bridge itself. 14 00:00:57,000 --> 00:01:01,000 So all of this ports on the switch are forwarding 15 00:01:01,000 --> 00:01:05,000 and all of these ports are designated ports 16 00:01:05,000 --> 00:01:08,000 so each port here is a designated port 17 00:01:08,000 --> 00:01:14,000 and the state of the port is forwarding. What about switch 3? 18 00:01:14,000 --> 00:01:22,000 so on switch 3 enable sh spanning-tree vlan 10 19 00:01:22,000 --> 00:01:28,000 we can see in the output that gigabit 0/0 is a designated port, it's forwarding 20 00:01:28,000 --> 00:01:33,000 so this is a designated port and the state is forwarding. 21 00:01:33,000 --> 00:01:37,000 We can see that gigabit 0/1 is a root port 22 00:01:37,000 --> 00:01:42,000 and its forwarding, so this is a root port and the state is forwarding 23 00:01:42,000 --> 00:01:48,000 and we can also see that gigabit 0/2 is a designated port and its forwarding. 24 00:01:48,000 --> 00:01:52,000 So this is a designated port and the state is forwarding. 25 00:01:52,000 --> 00:02:04,000 What about switch 4? so on switch 4 sh spanning-tree vlan 10 26 00:02:04,000 --> 00:02:10,000 on this switch, we’ve got 2 ports that are in VLAN 10. 27 00:02:10,000 --> 00:02:14,000 The reason why this port is not showing up is that this port is in VLAN 20 28 00:02:14,000 --> 00:02:21,000 and gigabit 0/0 is the root port and is forwarding and 0/1 is the designated port 29 00:02:21,000 --> 00:02:26,000 and is forwarding, so this is the root port and status forwarding. 30 00:02:26,000 --> 00:02:31,000 This is a designated port and state is forwarding 31 00:02:31,000 --> 00:02:35,000 This port is in different VLAN, so it's not shown for VLAN 10. 32 00:02:35,000 --> 00:02:38,000 So I’m hoping you can see a problem here. 33 00:02:38,000 --> 00:02:42,000 I’ll take another screen shot of this topology. 34 00:02:42,000 --> 00:02:46,000 What I want you to see is that this port 35 00:02:46,000 --> 00:02:52,000 this port and this port have been taken out of the topology 36 00:02:52,000 --> 00:02:56,000 because of the ports being blocked by Spanning Tree. 37 00:02:56,000 --> 00:03:00,000 User data is not gonna be sent through the blocking ports. 38 00:03:00,000 --> 00:03:04,000 So logically from a user point of view. 39 00:03:04,000 --> 00:03:08,000 These ports are not connected to the topology 40 00:03:08,000 --> 00:03:12,000 even though they're there while those ports on the blocking state 41 00:03:12,000 --> 00:03:15,000 user traffic doesn’t go through those ports. 42 00:03:15,000 --> 00:03:20,000 Other traffics such as CDP and LLDP will go through a blocking port 43 00:03:20,000 --> 00:03:25,000 but user traffic doesn’t. So what is that mean? 44 00:03:25,000 --> 00:03:31,000 If this user is sending large files as an example, to this server 45 00:03:31,000 --> 00:03:38,000 that traffic will flow this way to get to the server which is inefficient. 46 00:03:38,000 --> 00:03:42,000 Traffic from this host will go this path to get to this server. 47 00:03:42,000 --> 00:03:48,000 So if a large number of hosts here were sending traffic to the server 48 00:03:48,000 --> 00:03:53,000 that traffic is having to go across this link between the 2 core switches 49 00:03:53,000 --> 00:03:58,000 and it could be over run because we only have 1 link that’s enabled. 50 00:03:58,000 --> 00:04:03,000 So if I clear this diagram up 51 00:04:03,000 --> 00:04:06,000 we only have 1 forwarding link here. 52 00:04:06,000 --> 00:04:11,000 The other link is broken and the path used is inefficient. 53 00:04:11,000 --> 00:04:14,000 one of the things that you must remember with the Spanning Tree 54 00:04:14,000 --> 00:04:17,000 is you must set the Spanning Tree root 55 00:04:17,000 --> 00:04:19,000 you don’t wanna allow Spanning Tree to determine 56 00:04:19,000 --> 00:04:23,000 where the root is without your input 57 00:04:23,000 --> 00:04:26,000 because the situation could be a lot worst than it is currently. 58 00:04:26,000 --> 00:04:30,000 If this switch became the root bridge of the topology 59 00:04:30,000 --> 00:04:32,000 it could be a lot worst 60 00:04:32,000 --> 00:04:35,000 because this switch would use this as it's root port 61 00:04:35,000 --> 00:04:37,000 this switch would use this as it's root port 62 00:04:37,000 --> 00:04:39,000 and let’s assume that the MAC address of this switch 63 00:04:39,000 --> 00:04:41,000 is lower than the switch or has a lower priority 64 00:04:41,000 --> 00:04:45,000 that would mean that this would be the root port of this edge switch. 65 00:04:45,000 --> 00:04:49,000 This port and this port would be designated port 66 00:04:49,000 --> 00:04:51,000 this would be a designated port 67 00:04:51,000 --> 00:04:55,000 and in this topology assuming that this has a lower bridge ID 68 00:04:55,000 --> 00:04:58,000 these ports would be designated ports. 69 00:04:58,000 --> 00:05:02,000 Let’s assume that this has a lower bridge ID than this 70 00:05:02,000 --> 00:05:05,000 this would be a designated port in that scenario 71 00:05:05,000 --> 00:05:08,000 which means that this port is blocked 72 00:05:08,000 --> 00:05:11,000 this port gets blocked and this port gets blocked. 73 00:05:11,000 --> 00:05:17,000 So now if this host has to send a large number of files to this server 74 00:05:17,000 --> 00:05:22,000 the traffic will flow like this to get to the server. 75 00:05:22,000 --> 00:05:26,000 Assume once again that you have many, many host devices here 76 00:05:26,000 --> 00:05:32,000 they are sending all their traffic via this access switch to get to the server. 77 00:05:32,000 --> 00:05:40,000 If this was a lower end switch let’s say it’s very old 2950 access switch 78 00:05:40,000 --> 00:05:43,000 and it became the root of your topology 79 00:05:43,000 --> 00:05:48,000 you would be forcing lots of lots of user data through this little switch 80 00:05:48,000 --> 00:05:53,000 and the same would be true if you have many, many access switches 81 00:05:53,000 --> 00:05:56,000 so imagine you have 20 access switches here 82 00:05:56,000 --> 00:06:01,000 all the user traffic on those 20 access switches would now be pushed through 83 00:06:01,000 --> 00:06:04,000 the access switch to get to the server 84 00:06:04,000 --> 00:06:07,000 that’s definitely not what we want. 85 00:06:07,000 --> 00:06:14,000 We wanna make sure that the core switches of the root switches 86 00:06:14,000 --> 00:06:17,000 and to improve this we want to make sure 87 00:06:17,000 --> 00:06:20,000 that one of the switches is the root for some VLANs 88 00:06:20,000 --> 00:06:25,000 so in this topology, we gonna make switch 1, the root for VLAN 1 and VLAN 10 89 00:06:25,000 --> 00:06:28,000 and we're gonna make this switch the root for other VLANs 90 00:06:28,000 --> 00:06:31,000 now in this topology, we would split it as follows 91 00:06:31,000 --> 00:06:36,000 because VLAN 10 hosts are connected to this switch 92 00:06:36,000 --> 00:06:41,000 and it’s gonna be more efficient if they send traffic directly to that core switch 93 00:06:41,000 --> 00:06:46,000 and this host VLAN 20 send their traffic directly to switch 2. 94 00:06:46,000 --> 00:06:52,000 So in our topology, we're going to make this switch the root for VLAN 1 95 00:06:52,000 --> 00:06:57,000 and VLAN 10 and this switch will be the root for VLAN 20 96 00:06:57,000 --> 00:07:01,000 that means once again that VLAN 10 host will send their traffic there 97 00:07:01,000 --> 00:07:05,000 and VLAN 20 hosts will send their traffic there. 98 00:07:05,000 --> 00:07:10,000 So let’s set that up.