WEBVTT

1
00:00.000 --> 00:03.930
All right, we're jumping back into the lab here to take a look at cost

2
00:03.930 --> 00:05.600
configuration.

3
00:05.600 --> 00:07.640
And I've got this same topology here.

4
00:07.640 --> 00:09.950
Switch 5 is also down there, but it's not going to be part of this

5
00:09.950 --> 00:10.760
demonstration.

6
00:10.760 --> 00:14.160
We'll notice that we have a couple of links now between switch 2 and switch 4,

7
00:14.160 --> 00:14.320
which is

8
00:14.320 --> 00:18.120
going to play into our report priorities conversation coming up.

9
00:18.120 --> 00:21.360
Our focus is going to be on cost manipulation here.

10
00:21.360 --> 00:27.040
We're going to find that switch 4 has its link to switch 2.

11
00:27.040 --> 00:29.840
Both of these links actually are in a blocking state.

12
00:29.840 --> 00:34.170
And the reason for that is because, as we might recall from previous time
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

12
00:29.840 --> 00:34.170
And the reason for that is because, as we might recall from previous time

13
00:34.170 --> 00:34.640
suspended

14
00:34.640 --> 00:39.680
in this lab, that switch 3 has actually the best MAC address in the entire

15
00:39.680 --> 00:40.560
network.

16
00:40.560 --> 00:43.840
And so if I want to double check to make sure switch 1 is the root, I've got a

17
00:43.840 --> 00:44.300
priority

18
00:44.300 --> 00:48.320
statement on here that's going to make the root, or make switch 1 the root, it

19
00:48.320 --> 00:48.680
's set

20
00:48.680 --> 00:50.320
at 4K.

21
00:50.320 --> 00:54.640
And so the question is going to be, can I change the blocking port to be

22
00:54.640 --> 00:56.240
pointing now towards

23
00:56.240 --> 00:57.440
switch 3?

24
00:57.440 --> 01:02.480
So just to get some interfaces on here as well, this is going to be gig 1 0
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

24
00:57.440 --> 01:02.480
So just to get some interfaces on here as well, this is going to be gig 1 0

25
01:02.480 --> 01:03.520
here pointing

26
01:03.520 --> 01:04.960
to switch 3.

27
01:04.960 --> 01:11.840
And then we've got gig 0 slash 2 and 0 slash 3 going up to switch 2.

28
01:11.840 --> 01:14.320
So let's go ahead and take a look at this.

29
01:14.320 --> 01:17.680
I'll leave the diagram up as long as it's not in the way.

30
01:17.680 --> 01:22.520
And so switch 1, I'm going to do a show spanning tree VLAN 1 root.

31
01:22.520 --> 01:24.720
We'll just focus on VLAN 1 here.

32
01:24.720 --> 01:28.940
And we see no root port, which as we just talked about, there's means there's

33
01:28.940 --> 01:29.640
no upstream

34
01:29.640 --> 01:31.520
port, it means it is the root.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

34
01:29.640 --> 01:31.520
port, it means it is the root.

35
01:31.520 --> 01:34.600
So that is a good way to verify that.

36
01:34.600 --> 01:41.630
But also notice, if I do a show spanning tree, I'm going to find that the costs

37
01:41.630 --> 01:42.920
are 4 here

38
01:42.920 --> 01:46.920
and 4, that's a pretty good indication we're running the short path cost.

39
01:46.920 --> 01:49.400
Let's go and convert everything over to the long path cost.

40
01:49.400 --> 01:55.070
The way we do that, it's the global configuration and it's spanning tree path

41
01:55.070 --> 01:56.520
not patch cost,

42
01:56.520 --> 01:59.160
path cost, and then method.

43
01:59.160 --> 02:02.920
And we see that we've got short and long short is still the default method.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

43
01:59.160 --> 02:02.920
And we see that we've got short and long short is still the default method.

44
02:02.920 --> 02:05.800
So I'm going to change this to method long.

45
02:05.800 --> 02:11.870
So now if I do a show spanning tree, I'm going to find that my costs are now 20

46
02:11.870 --> 02:13.040
,000.

47
02:13.040 --> 02:14.360
It's the same bandwidth.

48
02:14.360 --> 02:19.090
It's still gig interfaces, but spanning tree considered it to have a cost of 20

49
02:19.090 --> 02:20.040
,000.

50
02:20.040 --> 02:23.360
So I'm going to go ahead and get on to switch to and switch through and do the

51
02:23.360 --> 02:24.120
same thing.

52
02:24.120 --> 02:31.770
So spanning tree path cost method long and switch three same thing, spanning
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

52
02:24.120 --> 02:31.770
So spanning tree path cost method long and switch three same thing, spanning

53
02:31.770 --> 02:32.640
tree path

54
02:32.640 --> 02:35.840
cost method long.

55
02:35.840 --> 02:37.480
So let's go over to switch four.

56
02:37.480 --> 02:40.100
And at this point, this is the only switch that's still running short path

57
02:40.100 --> 02:40.560
costs.

58
02:40.560 --> 02:45.360
If I do a show spanning tree for VLAN one, we'll see that first of all, we are

59
02:45.360 --> 02:46.080
blocking

60
02:46.080 --> 02:48.400
the ports that we expect to block.

61
02:48.400 --> 02:52.920
And we've got the root port still is gig one zero pointing to switch three, but

62
02:52.920 --> 02:53.520
the costs

63
02:53.520 --> 02:54.520
are still short.

64
02:54.520 --> 02:57.080
It's four on each interface.

65
02:57.080 --> 03:01.000
So then we glance up here to say, okay, well, what is my path cost to root?
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

65
02:57.080 --> 03:01.000
So then we glance up here to say, okay, well, what is my path cost to root?

66
03:01.000 --> 03:05.000
And we see it's 20,000 for the exact number we used in the chalkboarding

67
03:05.000 --> 03:05.960
session, but it's

68
03:05.960 --> 03:08.040
indicative of what's happening here.

69
03:08.040 --> 03:14.410
So if I look at this, what we have is we've got a cost of four on, whoops,

70
03:14.410 --> 03:15.760
wrong link,

71
03:15.760 --> 03:21.080
this link down here, but switch three has a cost link of 20,000.

72
03:21.080 --> 03:27.980
So it's advertising a cost of 20,000 in switch four doesn't have any idea

73
03:27.980 --> 03:29.040
whether switch

74
03:29.040 --> 03:34.580
three has long path costs or a static configuration or just an insanely long
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

74
03:29.040 --> 03:34.580
three has long path costs or a static configuration or just an insanely long

75
03:34.580 --> 03:36.120
path to the root.

76
03:36.120 --> 03:40.440
Either way, it's going to trust that it's a 20,000 cost being advertised.

77
03:40.440 --> 03:42.880
It's going to add its own four.

78
03:42.880 --> 03:46.120
And that's why it thinks it has a cost of 20,000 for.

79
03:46.120 --> 03:52.700
And so that's exactly what's happening and why we can technically mix and match

80
03:52.700 --> 03:53.200
our long

81
03:53.200 --> 03:54.560
and short path costs.

82
03:54.560 --> 03:57.200
We just don't ever want to do that in production.

83
03:57.200 --> 04:02.280
That would again, create some unexpected results at times.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

83
03:57.200 --> 04:02.280
That would again, create some unexpected results at times.

84
04:02.280 --> 04:03.520
So let's make it match.

85
04:03.520 --> 04:05.720
We're going to do the same configuration.

86
04:05.720 --> 04:10.040
So spanning tree path cost method long on switch four.

87
04:10.040 --> 04:15.420
And now we would expect it to see a root path cost of 20,000 plus 20,000 20,000

88
04:15.420 --> 04:15.800
for each

89
04:15.800 --> 04:17.560
link should be 40,000.

90
04:17.560 --> 04:21.980
If I do my show spanning tree, VLAN one root command, it also gives the root

91
04:21.980 --> 04:23.800
cost of 40,000.

92
04:23.800 --> 04:28.860
So there it is listed and everything should be fully synchronized at this point

93
04:28.860 --> 04:28.880
.

94
04:28.880 --> 04:34.210
So now we look at the scenario where once again, just like we talked about on
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

94
04:28.880 --> 04:34.210
So now we look at the scenario where once again, just like we talked about on

95
04:34.210 --> 04:34.680
in the

96
04:34.680 --> 04:38.400
chalkboard, let's say that switch three here, we want to avoid switch three.

97
04:38.400 --> 04:44.910
I really would rather block this link rather than both of the links to switch

98
04:44.910 --> 04:45.560
two.

99
04:45.560 --> 04:49.400
Now I can't have both of those links up at the same time, not without bundling

100
04:49.400 --> 04:50.160
them together

101
04:50.160 --> 04:51.680
as an ether channel.

102
04:51.680 --> 04:54.440
But since they're separate, I would going to have to, I'm going to have to have

103
04:54.440 --> 04:54.680
one

104
04:54.680 --> 04:55.680
of them blocked.

105
04:55.680 --> 04:56.680
But the other one could come up.

106
04:56.680 --> 05:00.920
It doesn't matter which one of these comes online, but let's say that I want to
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

106
04:56.680 --> 05:00.920
It doesn't matter which one of these comes online, but let's say that I want to

107
05:00.920 --> 05:01.120
block

108
05:01.120 --> 05:02.120
to switch three.

109
05:02.120 --> 05:03.120
What can I do?

110
05:03.120 --> 05:05.560
Well, this is where I can start to adjust the cost.

111
05:05.560 --> 05:08.040
So I could do one of two things here.

112
05:08.040 --> 05:16.480
I could consider increasing the cost here on gig one zero because right now I

113
05:16.480 --> 05:17.760
basically

114
05:17.760 --> 05:20.240
have the exact same cost coming in.

115
05:20.240 --> 05:22.240
This is 20k here.

116
05:22.240 --> 05:23.240
This is 20k.

117
05:23.240 --> 05:26.880
So both switches are advertising a root path cost of 20,000.

118
05:26.880 --> 05:29.040
I bring them in on gig interfaces.

119
05:29.040 --> 05:36.320
So either way, I've got a 40,000 path going to switch two and a 40,000 path
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

119
05:29.040 --> 05:36.320
So either way, I've got a 40,000 path going to switch two and a 40,000 path

120
05:36.320 --> 05:37.440
going to switch

121
05:37.440 --> 05:38.440
three.

122
05:38.440 --> 05:42.020
So the cost is identical right now, which is why I could increase the cost this

123
05:42.020 --> 05:42.480
way and

124
05:42.480 --> 05:45.560
make it maybe 80k or something like that.

125
05:45.560 --> 05:47.960
And then I would prefer the shorter path.

126
05:47.960 --> 05:54.120
Alternatively, I could lower the cost up here, maybe make it 5k.

127
05:54.120 --> 05:59.560
So at that point, this would be 25k, which is better than 40k.

128
05:59.560 --> 06:01.560
And so I would prefer that path.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

128
05:59.560 --> 06:01.560
And so I would prefer that path.

129
06:01.560 --> 06:06.900
It doesn't matter which one I choose, but I would have to manipulate one of

130
06:06.900 --> 06:07.480
these and

131
06:07.480 --> 06:09.920
you know, it could technically do both if we wanted to.

132
06:09.920 --> 06:11.520
So let's go ahead and do the first one.

133
06:11.520 --> 06:15.390
Let's increase cost over here because it only requires configuring a single

134
06:15.390 --> 06:15.880
link.

135
06:15.880 --> 06:20.710
We'll get on to gig one zero and we'll make this cost, let's just make it cost

136
06:20.710 --> 06:22.520
100,000.

137
06:22.520 --> 06:26.600
And so now our cost should be 120k.

138
06:26.600 --> 06:30.080
The advertised 20 plus my link cost of 100k.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

138
06:26.600 --> 06:30.080
The advertised 20 plus my link cost of 100k.

139
06:30.080 --> 06:31.080
Yeah, 100k.

140
06:31.080 --> 06:33.480
That's what we're talking about configuring.

141
06:33.480 --> 06:35.240
So I'm on switch four here.

142
06:35.240 --> 06:39.880
I'm going to get on to the interface and gig one slash zero.

143
06:39.880 --> 06:43.720
And now I've got the spanning tree cost command.

144
06:43.720 --> 06:49.880
Now notice if I do spanning tree cost 100,000, this is going to apply it to all

145
06:49.880 --> 06:50.800
the VLANs.

146
06:50.800 --> 06:56.590
Meanwhile, I could specify the VLAN VLAN one and then I can change the cost in

147
06:56.590 --> 06:57.200
the same

148
06:57.200 --> 06:58.200
way.

149
06:58.200 --> 07:03.690
It's just going to impact whether or not the cost is this, you know, placed for
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

149
06:58.200 --> 07:03.690
It's just going to impact whether or not the cost is this, you know, placed for

150
07:03.690 --> 07:04.400
all VLANs

151
07:04.400 --> 07:05.400
or just one.

152
07:05.400 --> 07:06.600
So we'll demonstrate that here in a moment.

153
07:06.600 --> 07:11.200
So I'm just going to set VLAN ones cost to 100,000.

154
07:11.200 --> 07:15.460
And then I can do this great command show spanning tree interface, gig one zero

155
07:15.460 --> 07:16.000
, and

156
07:16.000 --> 07:19.800
it shows me the cost on a per VLAN basis as well as the status.

157
07:19.800 --> 07:20.800
This is a great command.

158
07:20.800 --> 07:23.800
I want to see what's happening on a specific interface.

159
07:23.800 --> 07:27.800
And so we see the cost is 100,000, but only for VLAN one.

160
07:27.800 --> 07:33.440
VLANs 10, 20, and 30 are still using the default long path cost of 20k.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

160
07:27.800 --> 07:33.440
VLANs 10, 20, and 30 are still using the default long path cost of 20k.

161
07:33.440 --> 07:36.830
So at this point, we are expecting that switch four has moved this into a

162
07:36.830 --> 07:37.760
blocking state.

163
07:37.760 --> 07:42.560
I can do the show spanning tree blocked ports command.

164
07:42.560 --> 07:47.000
And for VLAN one, actually, that's the only VLAN that has blocked ports, we are

165
07:47.000 --> 07:47.240
still

166
07:47.240 --> 07:48.800
blocking an upstream port.

167
07:48.800 --> 07:54.280
And we had to unblock one of these, but it does appear that we have unblocked

168
07:54.280 --> 07:55.040
gig zero

169
07:55.040 --> 07:58.680
three kept keeping gig zero to a blocked state.

170
07:58.680 --> 08:04.480
And importantly, we are now blocking gig one slash zero.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

170
07:58.680 --> 08:04.480
And importantly, we are now blocking gig one slash zero.

171
08:04.480 --> 08:07.600
And so that's exactly what we wanted to have happen.

172
08:07.600 --> 08:10.900
So again, we could have manipulated the cost upstream over here, but we would

173
08:10.900 --> 08:11.280
have had

174
08:11.280 --> 08:13.160
to pick an interface.

175
08:13.160 --> 08:18.090
And so at this point, now we could say, hey, what if I wanted to block the

176
08:18.090 --> 08:18.760
other interface

177
08:18.760 --> 08:21.320
what if I wanted to block gig zero three?

178
08:21.320 --> 08:24.320
Well, I could make gig zero two more favorable.

179
08:24.320 --> 08:29.360
Because right now both of the costs coming in are being advertised as 20k

180
08:29.360 --> 08:30.240
received as
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

180
08:29.360 --> 08:30.240
received as

181
08:30.240 --> 08:31.240
20k.

182
08:31.240 --> 08:38.590
So if this is a 40k path and this is a 40k path, then they're favored the same

183
08:38.590 --> 08:39.080
and we're

184
08:39.080 --> 08:42.280
going to have to choose one based on the port priority concept that we talked

185
08:42.280 --> 08:44.240
about earlier.

186
08:44.240 --> 08:48.800
But what if I wanted to force to the path this way?

187
08:48.800 --> 08:51.120
What if I wanted to open this link up?

188
08:51.120 --> 08:58.700
Well, what I could do is leave this as a 20k cost, but then make this interface

189
08:58.700 --> 08:59.240
gig zero

190
08:59.240 --> 09:03.160
two, let's make this a 10k cost.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

190
08:59.240 --> 09:03.160
two, let's make this a 10k cost.

191
09:03.160 --> 09:06.240
And so let's go ahead and do that real quick.

192
09:06.240 --> 09:08.200
Remember this is an inbound configuration.

193
09:08.200 --> 09:10.600
So I can get on to interface gig zero two.

194
09:10.600 --> 09:16.000
This is the current blocked port and say, in fact, let's just do spanning tree

195
09:16.000 --> 09:16.560
cost.

196
09:16.560 --> 09:18.600
And I said I'd do 10,000.

197
09:18.600 --> 09:20.800
So spanning tree cost 10,000.

198
09:20.800 --> 09:27.600
Now if I do a show spanning tree gig interface gig zero two, there we go.

199
09:27.600 --> 09:29.040
We got it out.

200
09:29.040 --> 09:34.410
Notice that because I didn't specify a VLAN, now it's set the cost to be 10,000
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

200
09:29.040 --> 09:34.410
Notice that because I didn't specify a VLAN, now it's set the cost to be 10,000

201
09:34.410 --> 09:34.960
for all

202
09:34.960 --> 09:36.560
of the VLANs.

203
09:36.560 --> 09:43.660
And so if I do my show spanning tree VLAN one, we should now see that, yep, we

204
09:43.660 --> 09:44.160
are have

205
09:44.160 --> 09:46.360
declared gig zero two to be the root.

206
09:46.360 --> 09:48.280
We're still going through the listening and learning phases.

207
09:48.280 --> 09:49.480
We're almost done there.

208
09:49.480 --> 09:54.240
But gig zero three was placed into blocking, which means my final diagram is

209
09:54.240 --> 09:54.680
actually

210
09:54.680 --> 10:01.840
going to look like this, where I'm blocking these two links as shown.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

210
09:54.680 --> 10:01.840
going to look like this, where I'm blocking these two links as shown.

211
10:01.840 --> 10:04.160
And this link right here is indeed my root port.

212
10:04.160 --> 10:08.860
So I was able to do all of that on switch for using my spanning tree cost

213
10:08.860 --> 10:09.960
commands, keeping

214
10:09.960 --> 10:15.080
in mind that the cost manipulations go on to the inbound interfaces.

215
10:15.080 --> 10:19.080
And that's what allows me to determine which ports in the network are blocked

216
10:19.080 --> 10:19.520
and kind

217
10:19.520 --> 10:23.060
of go against the default settings that spanning tree would have decided

218
10:23.060 --> 10:23.680
otherwise.