1 00:00:15,890 --> 00:00:21,950 So let's look at optimizing spanning tree, Packet Tracer once again makes this easy. 2 00:00:21,950 --> 00:00:30,560 We can see that these ports are blocking in spanning tree and so is this port. To confirm that on core 3 00:00:30,560 --> 00:00:42,500 1 we can use the command show spanning tree various VLANs will be shown with this command here's 4 00:00:42,500 --> 00:00:55,610 VLAN 1 we can see that port gigabit 1 0 23 is forwarding 24 is blocking 1 0 1 is forwarding but 2 and 5 00:00:55,610 --> 00:01:09,420 3 are blocking for VLAN 1. For VLAN 10 the result is the same for VLAN 20 result is the same. 6 00:01:09,490 --> 00:01:15,460 Same is true for VLAN 30 and VLAN 100. Again 7 00:01:15,580 --> 00:01:23,380 the problem is if lots of PCs in the access layer want to send traffic to lots of servers over here 8 00:01:23,470 --> 00:01:31,600 in the network, all their traffic has to go via core 2, and then it's gonna be sent across the 9 00:01:31,600 --> 00:01:41,790 single gigabit 1 0 23 link to the servers that's not an optimal way of doing it. Now in a lot of cases 10 00:01:42,210 --> 00:01:49,110 access switches have multiple VLANs and you can improve the performance by sending some traffic using 11 00:01:49,110 --> 00:01:57,240 this uplink and some traffic using this uplink. At the moment no user traffic uses this uplink at 12 00:01:57,240 --> 00:02:04,680 all because this port is blocking, no traffic uses this uplink because this port is blocking, no 13 00:02:04,680 --> 00:02:12,180 traffic uses this uplink because this port is blocking and the same is true about gigabit 1 0 24. The 14 00:02:12,180 --> 00:02:19,980 only traffic that is permitted out of a spanning tree port and accepted in on a spanning tree port are 15 00:02:20,250 --> 00:02:30,680 network protocols such as CDP, LLDP, spanning tree and a few others. Normal user traffic cannot use any 16 00:02:30,680 --> 00:02:38,450 of these links effectively and logically those ports have been disconnected from the network so those 17 00:02:38,450 --> 00:02:45,980 links are therefore redundancy but we are wasting the bandwidth on those links so let's optimize these 18 00:02:45,980 --> 00:02:53,760 spanning tree network. We've been told that core 1 should be the root for odd VLANs and core 2 the 19 00:02:53,760 --> 00:03:02,630 root for even VLANs. Now in the exam, it will be more clear than that but let's assume that our odd 20 00:03:02,640 --> 00:03:10,730 VLANs or VLAN 1 10 and 30 and our even VLANs are 20 and 100. 21 00:03:11,250 --> 00:03:27,030 So on core 1 spanning tree, VLAN 1, root primary you can do it that way or you can specify priority 22 00:03:27,780 --> 00:03:29,560 and specify a priority. 23 00:03:29,900 --> 00:03:36,870 I like to use the property of 0 that lowers the spanning tree priority to the lowest possible 24 00:03:36,870 --> 00:03:44,640 number. In the exam, it'll be more clear about which option you should use. 25 00:03:44,640 --> 00:03:50,970 So for VLAN 1 10 and 30 I'm gonna make this switch the root. 26 00:03:50,970 --> 00:03:58,530 Notice how the colors have changed all ports are now forwarding they're green whereas before they won't 27 00:03:58,530 --> 00:04:09,570 green. On core 2 for those VLANs we wanna have that switch as the backup root you wanna keep 28 00:04:09,570 --> 00:04:21,940 your core switches as roots. So spanning tree VLAN 1 priority notice it needs to be in multiples of 29 00:04:21,940 --> 00:04:33,910 4096, so for VLAN 1, VLAN 10 and VLAN 30 we're going to make that switch 30 00:04:34,270 --> 00:04:44,420 the backup root. So now when we look at core 1 show spanning tree VLAN 1. 31 00:04:44,480 --> 00:04:50,030 Notice this switch is the root switch for VLAN 1. 32 00:04:50,090 --> 00:04:51,840 It has a priority of one. 33 00:04:52,040 --> 00:04:59,420 The reason why it's a priority of one is that the priority is determined by the actual priority plus 34 00:04:59,480 --> 00:05:00,210 the VLAN 35 00:05:00,210 --> 00:05:08,240 number notice priorities 0 plus extended system ID. So 0 plus 1 is 1 giving the local switch a priority 36 00:05:08,240 --> 00:05:10,720 of 1 and the switch is the root 37 00:05:10,790 --> 00:05:14,480 so that's the priority of the root switch. 38 00:05:14,480 --> 00:05:15,890 When we look at the ports 39 00:05:15,890 --> 00:05:18,170 notice all ports are forwarding. 40 00:05:18,170 --> 00:05:29,110 What about the second switch core 2? Show spanning tree VLAN 1 what you'll notice is all ports are forwarding 41 00:05:29,620 --> 00:05:30,920 except for gigabit 42 00:05:30,950 --> 00:05:32,810 1 0 24. 43 00:05:33,010 --> 00:05:40,250 Now the indicators in packet tracer are green because it's not showing us the output for all VLANs 44 00:05:41,020 --> 00:05:43,540 the VLANs do differ. 45 00:05:43,540 --> 00:05:48,580 So as an example back on core 1 show spanning tree VLAN 20. 46 00:05:48,700 --> 00:05:53,550 Notice a lot of ports are still blocking on this switch. 47 00:05:53,680 --> 00:05:58,960 So core 1 is not the root for VLAN 20. 48 00:05:59,170 --> 00:06:09,080 Another switch is the root for VLAN 20 if we have a look on core 2 show spanning tree VLAN 20 this 49 00:06:09,170 --> 00:06:18,250 switch is the root for that VLAN, VLAN 20 and it has all ports forwarding. So packet tracer 50 00:06:18,430 --> 00:06:22,620 and the real switch will not show amber or orange 51 00:06:22,780 --> 00:06:30,070 if you're using per VLAN spanning tree and a trunk port is blocking on some VLANs and not on other 52 00:06:30,070 --> 00:06:31,480 VLANs. 53 00:06:31,480 --> 00:06:40,480 Okay, so show run pipe include spanning tree that's the configuration thus far under the switch show 54 00:06:40,480 --> 00:06:50,200 run pipe include spanning tree that's our configuration. Notice we can specify all VLANs in one 55 00:06:50,200 --> 00:07:01,680 go by doing the following. So we want this switch to be the root for VLANs 20 and VLANs 100. 56 00:07:02,790 --> 00:07:12,460 So spanning tree VLAN 20 and 100 priority 0, on this side spanning tree VLAN 20 57 00:07:12,460 --> 00:07:16,840 100 priority 4096. 58 00:07:16,840 --> 00:07:24,610 It's good practice to have your core switches being root switches and backup routes for other VLANs. 59 00:07:26,550 --> 00:07:35,550 So show spanning tree VLAN 20 notice it's still going through different states previously however 60 00:07:35,580 --> 00:07:45,300 we had a lot of blocking ports for VLAN 20 on core 1 that will hopefully now improve and there you 61 00:07:45,300 --> 00:07:46,080 go. 62 00:07:46,080 --> 00:07:53,140 The only port that's blocking is gigabit 1 0 24 for that VLAN. 63 00:07:53,370 --> 00:07:57,870 All other ports are forwarding so that's much better. 64 00:07:57,870 --> 00:08:07,640 We've been able to optimize spanning tree by making core 1 the root for some VLANs and core 2 65 00:08:07,640 --> 00:08:10,200 the root for other VLANs. 66 00:08:10,260 --> 00:08:19,260 That means that if we had VLAN 10 and 20 connected to this switch, VLAN 10 traffic would take this 67 00:08:19,260 --> 00:08:27,740 uplink VLAN 20 traffic would take this uplink and on the switch VLAN 10 would go to core 1 68 00:08:27,750 --> 00:08:38,460 VLAN 20 would go to core 2 and on this switch VLAN 30 would go to core 1, VLAN 20 would go to core 69 00:08:38,460 --> 00:08:46,540 2. We still have a problem however because the links between the two switches are still blocking. 70 00:08:46,570 --> 00:08:59,080 So again show spanning tree VLAN 20 notice on core 1 this port is blocking for VLAN 20 and 71 00:08:59,080 --> 00:09:10,530 it's blocking for VLAN 100 hundred, on this side show spanning tree VLAN 1 port 24 is blocking for 72 00:09:10,530 --> 00:09:23,130 VLAN 1 for VLAN 10 and for VLAN 30 we wanna combine or join these two links in an ether channel 73 00:09:23,370 --> 00:09:25,510 to get better throughput. 74 00:09:25,890 --> 00:09:28,310 So that's what we're gonna do in the next video.