-: Troubleshooting problems. 2 2
So in the last couple of lectures, 3 3
we talked about the methodology for troubleshooting, 4 4
and then we went through layers one, two, and three, 5 5
and wireless networking issues. 6 6
Now in this lesson, I'm going to give you 7 7
a couple of problems to test your knowledge. 8 8
After I present the problem, pause the video, 9 9
try to come up with the solution on your own, 10 10
and then restart the video and see 11 11
if you go the right answer. 12 12
The first problem I have is that 13 13
I have a PC one here that can't talk to server one. 14 14
They're both on the same network 15 15
'cause they're both to the left of the router. 16 16
Notice that I have a cat five e patch cable 17 17
going between my PC and the switch, 18 18
and I have cat six patch cables between 19 19
switch one, switch two, the server, and router one. 20 20
But whenever PC one tries to connect 21 21
to the server, it gets an error. 22 22
Why can't the client reach the server? 23 23
Go ahead and pause the video here 24 24
and come up with your solution. 25 25
Welcome back, so what did you come up with? 26 26
Let's take a look at this problem 27 27
and see where the issue might lie. 28 28
Now one of the key words in this problem 29 29
is that those switches are old 30 30
and they don't support MDIX. 31 31
Do you remember what MDIX did? 32 32
That's right, it allows you to 33 33
not have to use a crossover cable. 34 34
But because these switches don't support MDIX, 35 35
we have to have a crossover cable 36 36
between switch one and switch two. 37 37
And that's the issue here. 38 38
So to solve this problem, I need to replace 39 39
that patch cable with a crossover cable. 40 40
Whenever you hear the word patch cable, 41 41
remember a patch cable is a straight through cable. 42 42
And when you're dealing with old switches, 43 43
you need to use a crossover cable. 44 44
Anytime you connect two things 45 45
that are the same, like a PC to a PC, 46 46
a switch to a switch, a router to a router, 47 47
you have to use a crossover cable, 48 48
or they have to support MDIX. 49 49
Let's look at the second problem. 50 50
My second problem is the same type of network. 51 51
But now I've replaced that cable 52 52
with a fiber patch cable that allowed me to do crossover. 53 53
PC one is still unable to reach server one though. 54 54
You've verified there was communication 55 55
between switch one and switch two now, 56 56
because we replaced that fiber cable 57 57
and switched the transmit and receive. 58 58
Now why can't PC one talk to server one? 59 59
Go ahead and pause the video and come back 60 60
when you're ready to answer the question. 61 61
Alright, so let's take a look at 62 62
what is causing the problem. 63 63
Well, notice in this one we have three VLANs. 64 64
We have VLAN 100, VLAN 200, and VLAN 300. 65 65
So what do you think the problem is? 66 66
That's right, the VLANs aren't being routed. 67 67
Anytime you have different VLANs, 68 68
you have to have routers there. 69 69
And since this is a logical diagram, 70 70
we should have some method to show 71 71
that there is a logical router, 72 72
either that these are multilayer switches, 73 73
like layer three, or that they are routing 74 74
the traffic through the router. 75 75
In this case, we have neither of those, 76 76
and so our problem is that VLAN 100 77 77
only gets to switch one, VLAN 300 78 78
only gets to switch two, and VLAN 200 79 79
only goes between switch one and switch two. 80 80
And because we have three different VLANs, 81 81
we have to have routers to route that traffic. 82 82
Alright, now we have our third problem. 83 83
This one is going to be a layer three issue. 84 84
So PC one still can't reach server one. 85 85
We have verified that we have communication 86 86
between switch one and switch two, 87 87
but we still can't get all the way 88 88
from PC one down to server one. 89 89
What could be the problem this time? 90 90
I'm going to go ahead and pause the video 91 91
and let you think about this. 92 92
Alright you're back, are you ready to give me the answer? 93 93
Let's see if you got this one. 94 94
This one was a little bit tricky 95 95
and a little bit hard. 96 96
Notice I have three IP addresses on the screen. 97 97
I have on the router one interface, 98 98
10 dot zero dot one dot 65 slash 26, 99 99
and then I have on PC one, 100 100
10 dot zero dot one dot 62 slash 26, 101 101
and I have server one at 102 102
10 dot zero dot one dot 67 slash 26. 103 103
Now notice the special thing here 104 104
is that CIDR notation, they're all slash 26 subnets. 105 105
But are they on the same subnet? 106 106
Well maybe, let's take a look at it. 107 107
What is your slash 26 networks? 108 108
If you had a slash 24, all of these machines, 109 109
as long as they're within the 256 scope, 110 110
the dot zero through dot 255 would be in the same network. 111 111
But because it's a slash 26, 112 112
we're actually splitting up that network 113 113
into four subnets. 114 114
Those four subnets are 10 dot zero dot one dot zero, 115 115
10 dot zero dot one dot 64, 116 116
10 dot zero dot one dot 128, 117 117
and 10 dot zero dot one dot 192. 118 118
So the problem is all three of these IPs 119 119
are not in the same subnet. 120 120
We have the dot 62 in one subnet, 121 121
and the dot 65 and dot 67 in the second subnet. 122 122
And you can see that here, 123 123
illustrated with PC one being dot 62 124 124
in blue 125 125
and the other two being dot 65 and dot 67 in red. 126 126
How are we going to solve this problem? 127 127
Well we're going to have to move PC one into the second subnet 128 128
by assigning it an address of something over dot 64 129 129
and less then dot 128. 130 130
So in this case our router is dot 65, 131 131
if dot 66 or dot 68 was available, 132 132
we could use that and give it 133 133
a new IP of 10 dot zero dot one dot 68 slash 26 134 134
and now all three will be on the same subnet 135 135
and they'll be able to communicate to each other. 136 136
Our fourth problem is a wireless issue. 137 137
I have a two story building with 138 138
one access point on each floor. 139 139
They do have a proper overlap of 10 to 15% of coverage, 140 140
but users keep complaining that their WI-FI service 141 141
is dropping, what do you think is the design flaw? 142 142
Go ahead and pause the video and then 143 143
we'll come back and explain it. 144 144
Welcome back, alright, so have you 145 145
figured out the design flaw? 146 146
It's not a placement issue here 147 147
because we do have proper coverage 148 148
and we're covering the entire floor. 149 149
Instead it has to do with the configuration. 150 150
Let's look at access point one. 151 151
It's 802 dot 11n, operating in the 152 152
2.4 gigahertz spectrum. 153 153
It's operating on channel one, 154 154
it's using WPA two encryption and it's SSID is office. 155 155
When I look at access point two, 156 156
it's type matches, it's 802 dot 11n. 157 157
It's band matches, it's 2.4 gigahertz. 158 158
It's encryption matches, it's WPA two, 159 159
and it's SSID matches, which is office. 160 160
But it's channel is channel five. 161 161
Now why's that a problem? 162 162
If you remember back to our frequencies 163 163
and WI-FI lecture, you remember that we said 164 164
channels one, six, and 11 gave you the widest 165 165
distribution of channels and the least 166 166
amount of interference. 167 167
If you use something like one and five, 168 168
or one and four, that would be too close 169 169
together in the channels and that 170 170
can cause RFI or radio frequency interference, 171 171
and cause drops for your users. 172 172
In this case, that's the problem. 173 173
Because we're using channel one and channel five 174 174
in a small overlapping space, we're getting RFI issues. 175 175
And so to solve this, we would change 176 176
channel five to channel six or to channel 11 177 177
and that would solve our issue here.