WEBVTT 1 00:00.000 --> 00:02.780 All right, let's go and jump into this lab task. 2 00:02.780 --> 00:04.500 We want to make sure we know how to manipulate this 3 00:04.500 --> 00:08.040 spanning tree topology, whether it's inbound or outbound methods, 4 00:08.040 --> 00:10.360 and then we want to check port fast as well. 5 00:10.360 --> 00:12.240 So challenge task number one here. 6 00:12.240 --> 00:15.520 Ensure that switch five chooses the path through switch four. 7 00:15.520 --> 00:17.760 That'd be gig three slash one here. 8 00:17.760 --> 00:20.800 And we want to make sure that is the root port. 9 00:20.800 --> 00:25.240 Now, given that our BPDs are flowing downstream from the root, 10 00:25.240 --> 00:28.120 which we might want to do a discovery to make sure we know which 11 00:28.120 --> 00:28.880 switch is the root. 12 00:28.880 --> 00:31.120 It'll be switch one in this case. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 12 00:28.880 --> 00:31.120 It'll be switch one in this case. 13 00:31.120 --> 00:32.960 From there, we can understand that we probably 14 00:32.960 --> 00:34.800 need to use an inbound method here. 15 00:34.800 --> 00:36.720 I mean, we're really only using port priorities 16 00:36.720 --> 00:39.360 in the situation up here where we have multiple ports 17 00:39.360 --> 00:41.360 between two switches. 18 00:41.360 --> 00:46.040 But now we've got switches due to different switches upstream. 19 00:46.040 --> 00:49.880 And so looking at this, we want to do a discovery. 20 00:49.880 --> 00:52.560 We want to make sure that we're not making bad assumptions. 21 00:52.560 --> 00:55.000 But also, my starting assumption would 22 00:55.000 --> 00:58.720 be that this port is probably in a blocking state. 23 00:58.720 --> 01:01.680 Simply because it's further away from the root. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 23 00:58.720 --> 01:01.680 Simply because it's further away from the root. 24 01:01.680 --> 01:04.040 Now, if we look at things just from a hop perspective, 25 01:04.040 --> 01:05.800 we go to switch three, and then we 26 01:05.800 --> 01:08.560 see switch five and switch four are the same distance 27 01:08.560 --> 01:11.320 from the root, at which point switch four could also 28 01:11.320 --> 01:12.280 be blocking. 29 01:12.280 --> 01:14.400 And so let's go ahead and go out and take a look 30 01:14.400 --> 01:17.920 and see what exactly is happening in the lab. 31 01:17.920 --> 01:21.400 I'm going to go to switch five, do a show, spanning tree, 32 01:21.400 --> 01:22.920 blocked ports. 33 01:22.920 --> 01:24.960 And we do see that gig three slash one, 34 01:24.960 --> 01:27.880 that link on the left is in the blocking state. 35 01:27.880 --> 01:29.440 So I can do a number of things here. 36 01:29.440 --> 01:31.680 First of all, I could do a show spanning tree, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 36 01:29.440 --> 01:31.680 First of all, I could do a show spanning tree, 37 01:31.680 --> 01:34.400 and I could take a look at the information, especially 38 01:34.400 --> 01:36.360 what my cost to the root is. 39 01:36.360 --> 01:38.000 It says it's eight. 40 01:38.000 --> 01:41.400 And I could also do a show spanning tree, pick a VLAN, 41 01:41.400 --> 01:43.160 and then say root. 42 01:43.160 --> 01:44.760 And I get the same information. 43 01:44.760 --> 01:45.760 My root cost is eight. 44 01:45.760 --> 01:48.160 So a couple of different places to discover that. 45 01:48.160 --> 01:50.200 So looking back at the diagram here, 46 01:50.200 --> 01:54.560 given that gig interfaces have a path cost of four, 47 01:54.560 --> 01:57.320 it's probably pretty safe to look at this and say, OK, 48 01:57.320 --> 02:00.200 so it's probably four and four is my eight. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 48 01:57.320 --> 02:00.200 so it's probably four and four is my eight. 49 02:00.200 --> 02:01.360 And I can verify that. 50 02:01.360 --> 02:03.040 I don't have to assume anything. 51 02:03.040 --> 02:05.880 When I look up here, for example, gig two slash one 52 02:05.880 --> 02:10.440 and three slash one, it shows that it has path cost of four 53 02:10.440 --> 02:11.120 on that link. 54 02:11.120 --> 02:12.840 And then I could go to switch to and verify, 55 02:12.840 --> 02:15.920 although given that there's only one link left in the path, 56 02:15.920 --> 02:19.920 it's got to be four, given that the total path cost is eight. 57 02:19.920 --> 02:23.880 Now that configuration also told us that this path cost is four. 58 02:23.880 --> 02:26.080 And we could probably go out and verify this, 59 02:26.080 --> 02:29.160 but I will just say that this path link here is also four. 60 02:29.160 --> 02:31.520 We left all the costs default. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 60 02:29.160 --> 02:31.520 We left all the costs default. 61 02:31.520 --> 02:36.640 So if I want to prefer this path versus this winding path, 62 02:36.640 --> 02:40.160 well, then I'm going to have to compare eight versus 12, 63 02:40.160 --> 02:43.280 which means I'm going to have to either seriously decrease 64 02:43.280 --> 02:46.200 this, which is not mathematically possible. 65 02:46.200 --> 02:48.560 I can't make it so that it's negative, 66 02:48.560 --> 02:51.760 because I'm already looking at a path cost of eight this way. 67 02:51.760 --> 02:55.960 I'd have to make this somehow negative to get that below eight. 68 02:55.960 --> 02:59.880 So what I'm going to have to do is increase the cost on this link. 69 02:59.880 --> 03:02.840 And I need to make sure that the total path cost this way WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 69 02:59.880 --> 03:02.840 And I need to make sure that the total path cost this way 70 03:02.840 --> 03:05.400 is greater than this direction. 71 03:05.400 --> 03:08.800 So basically, I need to make it so that the total path cost 72 03:08.800 --> 03:09.960 is greater than eight. 73 03:09.960 --> 03:13.600 So I'm going to go ahead and get on here to interface gig 74 03:13.600 --> 03:15.640 two slash one, that'd be the link on the left. 75 03:15.640 --> 03:17.960 I'm going to say spanning tree cost, 76 03:17.960 --> 03:19.880 and I'll just add 10 to it. 77 03:19.880 --> 03:22.960 That should make the total path cost 14. 78 03:22.960 --> 03:26.040 So while spanning tree sorts that out, 79 03:26.040 --> 03:28.000 we basically turn this into 10. 80 03:28.000 --> 03:32.040 So now this should be 14, and this will still be 12. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 80 03:28.000 --> 03:32.040 So now this should be 14, and this will still be 12. 81 03:32.040 --> 03:34.600 So let's go and confirm that the blocked port moved. 82 03:34.600 --> 03:36.680 We're expecting this is no longer blocking, 83 03:36.680 --> 03:39.720 but this should be blocking gig two slash one, 84 03:39.720 --> 03:43.440 and show spanning tree blocked ports. 85 03:43.440 --> 03:46.120 Indeed shows gig two slash one. 86 03:46.120 --> 03:48.280 So on to task number two, and task number two 87 03:48.280 --> 03:50.560 is actually a little bit diabolical. 88 03:50.560 --> 03:53.760 So if you got it, then really good job, 89 03:53.760 --> 03:55.360 because we're going to have to use all of our knowledge 90 03:55.360 --> 03:56.760 to solve task two. 91 03:56.760 --> 04:00.200 Task two says that switch four wants us to pick gig zero two WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 91 03:56.760 --> 04:00.200 Task two says that switch four wants us to pick gig zero two 92 04:00.200 --> 04:03.800 as the root port, and we're not to configure switch four 93 04:03.800 --> 04:04.640 at all for this. 94 04:04.640 --> 04:07.120 So we might immediately say, OK, well, good. 95 04:07.120 --> 04:08.520 If I can't configure switch four, 96 04:08.520 --> 04:12.840 I know I can push policy down via the port priority here 97 04:12.840 --> 04:14.240 from switch two. 98 04:14.240 --> 04:15.680 Now we have to look at this and say, 99 04:15.680 --> 04:19.440 which one are we expecting to have the port blocked? 100 04:19.440 --> 04:21.720 I might say that, well, gig zero two is already lower 101 04:21.720 --> 04:24.280 than gig zero three, and so that should be the blocking 102 04:24.280 --> 04:25.680 port on the left. 103 04:25.680 --> 04:27.320 But remember, it's from the perspective 104 04:27.320 --> 04:29.600 of the upstream device when we're talking 105 04:29.600 --> 04:30.720 about port priorities. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 105 04:29.600 --> 04:30.720 about port priorities. 106 04:30.720 --> 04:32.880 It's an outbound concept. 107 04:32.880 --> 04:35.800 So it's actually gig zero two that's preferred, 108 04:35.800 --> 04:39.600 which means that probably gig, well, gig zero three 109 04:39.600 --> 04:40.960 from the switch two's perspective, 110 04:40.960 --> 04:43.320 but gig zero two on the other side of the link 111 04:43.320 --> 04:45.360 is probably in the blocking state. 112 04:45.360 --> 04:46.720 And now this is an assumption. 113 04:46.720 --> 04:50.480 So let's go ahead and go and take a look at switch four 114 04:50.480 --> 04:52.040 and find out if our assumption is valid. 115 04:52.040 --> 04:55.960 So show spanning tree blocked ports. 116 04:55.960 --> 04:56.720 Now look at that. 117 04:56.720 --> 04:58.520 Our assumption is not valid. 118 04:58.520 --> 05:02.160 This is where this lab task gets a little bit diabolical. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 118 04:58.520 --> 05:02.160 This is where this lab task gets a little bit diabolical. 119 05:02.160 --> 05:05.000 So we actually find that both of these ports 120 05:05.000 --> 05:09.200 are being blocked, which means that gig one zero must actually 121 05:09.200 --> 05:10.920 be the root. 122 05:10.920 --> 05:17.120 Now the root port here is determined by cost. 123 05:17.120 --> 05:21.880 And so therefore, we must assume that either the costs are-- 124 05:21.880 --> 05:24.000 is better this way, or it's a tie, 125 05:24.000 --> 05:26.960 and switch three wins the tiebreaker between switch two. 126 05:26.960 --> 05:29.680 And that's actually the case in this lab environment. 127 05:29.680 --> 05:31.640 So this is interesting. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 127 05:29.680 --> 05:31.640 So this is interesting. 128 05:31.640 --> 05:35.000 I am not allowed to change switch four's configuration. 129 05:35.000 --> 05:39.280 And I yet have to make it so that gig zero two here 130 05:39.280 --> 05:40.560 is the root port. 131 05:40.560 --> 05:42.440 How do I go about doing that? 132 05:42.440 --> 05:46.880 Well, the lab task didn't say that I can't configure switch three. 133 05:46.880 --> 05:48.960 So let's go ahead and head over to switch three 134 05:48.960 --> 05:50.360 and do a configuration. 135 05:50.360 --> 05:54.200 Now what can I do in order to make switch four 136 05:54.200 --> 05:57.840 want to block this port and open up one of these? 137 05:57.840 --> 05:59.600 Well, think back to what I just said. 138 05:59.600 --> 06:04.240 In this lab scenario, we have equal costs everywhere, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 138 05:59.600 --> 06:04.240 In this lab scenario, we have equal costs everywhere, 139 06:04.240 --> 06:06.280 which means that it's a tie right now. 140 06:06.280 --> 06:09.800 Eight this way, eight that way, and switch three 141 06:09.800 --> 06:11.160 just wins the tiebreaker. 142 06:11.160 --> 06:13.920 So I just have to make sure there's no tiebreaker here. 143 06:13.920 --> 06:17.720 I need to make sure that the path this way is worse 144 06:17.720 --> 06:19.320 than the path this way. 145 06:19.320 --> 06:21.040 But I can't configure switch four for this. 146 06:21.040 --> 06:22.480 So what am I going to do? 147 06:22.480 --> 06:24.560 I'm going to configure switch three. 148 06:24.560 --> 06:28.320 And I want to make sure that it sees that link as a link cost 149 06:28.320 --> 06:30.080 higher than four. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 149 06:28.320 --> 06:30.080 higher than four. 150 06:30.080 --> 06:32.160 And it really could just be anything higher than four. 151 06:32.160 --> 06:33.560 It could truly be five. 152 06:33.560 --> 06:40.960 So gig zero two on switch three interface gig zero two, 153 06:40.960 --> 06:44.240 I'm going to do spanning tree VLAN one cost. 154 06:44.240 --> 06:45.280 And let's just do five. 155 06:45.280 --> 06:47.600 Let's just see if that actually works. 156 06:47.600 --> 06:50.680 So let's head over to switch four and find out if that worked. 157 06:50.680 --> 06:53.640 So I'm going to do a show spanning tree blocked ports. 158 06:53.640 --> 06:57.400 And we are indeed blocking towards switch three now. 159 06:57.400 --> 06:59.680 And now we just have to resolve the fact 160 06:59.680 --> 07:02.640 that we don't want to block gig zero two. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 160 06:59.680 --> 07:02.640 that we don't want to block gig zero two. 161 07:02.640 --> 07:05.640 We want to block gig zero three according to our diagram. 162 07:05.640 --> 07:06.600 Let's just confirm that. 163 07:06.600 --> 07:07.240 Yes. 164 07:07.240 --> 07:10.000 So we want to make gig zero to the root port. 165 07:10.000 --> 07:15.920 The good news is that gig zero three is no longer blocking. 166 07:15.920 --> 07:18.440 Instead, it's gig one zero that's blocking. 167 07:18.440 --> 07:19.960 So we're halfway there. 168 07:19.960 --> 07:22.560 Like I said, this task is a little bit diabolical. 169 07:22.560 --> 07:26.320 So now we need to worry about the port priority on switch two 170 07:26.320 --> 07:30.520 to try to make it so gig zero two goes into a forwarding state WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 170 07:26.320 --> 07:30.520 to try to make it so gig zero two goes into a forwarding state 171 07:30.520 --> 07:32.000 and is no longer blocking. 172 07:32.000 --> 07:33.080 How do we do that? 173 07:33.080 --> 07:36.400 Well, again, we favor gig zero two because it's lower. 174 07:36.400 --> 07:40.040 So maybe we should lower the port priority on gig zero three. 175 07:40.040 --> 07:41.520 Well, what was that default value? 176 07:41.520 --> 07:43.400 Again, it was 128. 177 07:43.400 --> 07:48.520 And so anything less than 128, including 112, for example, 178 07:48.520 --> 07:49.680 would work just fine here. 179 07:49.680 --> 07:53.920 It would make gig zero three the favored port over gig zero two. 180 07:53.920 --> 07:58.120 And then that pushes down and opens up this port. 181 07:58.120 --> 07:59.680 So let's get on to switch two and configure it 182 07:59.680 --> 08:03.800 to the port priority of 112 on gig zero three. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 182 07:59.680 --> 08:03.800 to the port priority of 112 on gig zero three. 183 08:03.800 --> 08:07.480 Switch two, gig zero three. 184 08:07.480 --> 08:11.560 Switch two, gig zero three, spanning tree VLAN one, 185 08:11.560 --> 08:14.760 port priority, and then we said 112. 186 08:14.760 --> 08:18.920 So now let's go to switch four and run that show spanning tree 187 08:18.920 --> 08:21.040 blocked command and look at that already. 188 08:21.040 --> 08:24.320 It has moved the block over to gig zero three. 189 08:24.320 --> 08:27.760 We're still blocking on gig zero one zero that heads to switch 190 08:27.760 --> 08:28.520 three. 191 08:28.520 --> 08:30.600 And then as far as this task is concerned, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 191 08:28.520 --> 08:30.600 And then as far as this task is concerned, 192 08:30.600 --> 08:32.720 we said that we wanted to select gig zero two 193 08:32.720 --> 08:34.040 as its path to root. 194 08:34.040 --> 08:38.240 We can always confirm that by using the show spanning tree 195 08:38.240 --> 08:39.400 root command. 196 08:39.400 --> 08:42.240 And so my root port is indeed gig zero two. 197 08:42.240 --> 08:44.040 So that lab task is complete. 198 08:44.040 --> 08:47.640 Now, lastly, the final lab task is switch five, 199 08:47.640 --> 08:51.400 making sure no TCNs are sent if gig three slash two 200 08:51.400 --> 08:53.400 transitions to the forwarding state. 201 08:53.400 --> 08:57.640 That is simply configuring spanning tree port fast. 202 08:57.640 --> 09:02.760 So I can say spanning tree port fast on it gig three slash two. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 202 08:57.640 --> 09:02.760 So I can say spanning tree port fast on it gig three slash two. 203 09:02.760 --> 09:04.080 And that is the end of that task. 204 09:04.080 --> 09:06.880 So far let's dive algal then task number one. 205 09:06.880 --> 09:08.840 Just keep in mind that we could have configured 206 09:08.840 --> 09:10.400 spanning tree port fast. 207 09:10.400 --> 09:13.480 Well, you know, made that an access port and then pushed it out 208 09:13.480 --> 09:14.440 by default. 209 09:14.440 --> 09:16.760 If it was a trunk, we would have needed to specify the trunk 210 09:16.760 --> 09:20.080 keyword, but we just kept it simple and made sure that we 211 09:20.080 --> 09:24.240 understand that port fast does indeed squelch those TCNs. 212 09:24.240 --> 09:27.160 So this lab task, again, or this set of lab tasks again 213 09:27.160 --> 09:29.400 was a little bit of a challenge. 214 09:29.400 --> 09:32.280 So hopefully walked through that and maybe flagged this one WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 214 09:29.400 --> 09:32.280 So hopefully walked through that and maybe flagged this one 215 09:32.280 --> 09:34.960 for later so that you can come back and do this again 216 09:34.960 --> 09:37.200 and make sure that we've got it all down between cost 217 09:37.200 --> 09:39.040 and port priority configurations. 218 09:39.040 --> 09:40.400 I hope this has been informative for you. 219 09:40.400 --> 09:42.600 And I'd like to thank you for viewing.