-: Sensors. 2 2
In this lesson, 3 3
we're going to talk about sensors 4 4
that help us monitor the performance of our network devices, 5 5
those devices like routers, switches, and firewalls. 6 6
Now, these sensors can be used to monitor 7 7
the device's temperature, its CPU usage, and its memory, 8 8
and these things can be key indicators 9 9
of whether a device is operating properly 10 10
or is about to suffer a catastrophic failure. 11 11
Our first sensor measurement we need to talk about 12 12
is the temperature of the device. 13 13
Now, most network devices like your routers, 14 14
switches, and firewalls 15 15
have the ability to report on the temperature 16 16
within their chasses. 17 17
Now, depending on the model, 18 18
there may be only one or two temperature readings 19 19
or on some larger enterprise devices, 20 20
you may have a temperature reading 21 21
on each and every controller, processor, interface card, 22 22
and thing like that inside the system. 23 23
Now, the temperature centers 24 24
can be used to measure the air temperature 25 25
inside the intake outlet 26 26
and the air temperature at the exhaust outlet at a minimum. 27 27
Now, for each of these sensors, 28 28
you can set up minor and major temperature thresholds. 29 29
A minor temperature threshold is used to set off an alarm 30 30
when a rising temperature is detected, 31 31
but it hasn't reached dangerous levels yet. 32 32
When this occurs, 33 33
a system message is displayed, 34 34
an SNMP notification is sent, 35 35
and an environmental alarm can be sounded. 36 36
Now, when you have a major temperature threshold, 37 37
this is going to be used to set off an alarm 38 38
when the temperature reaches dangerous conditions. 39 39
At this level, we want to still display those system messages, 40 40
get that SNMP notification, 41 41
and have the environmental alarm sounded. 42 42
But in addition to that, 43 43
the device can actually start to load shed 44 44
by turning off different functions to reduce the temperature 45 45
being generated by the device's processor. 46 46
For example, let's say you have a router 47 47
with multiple processing cards in it. 48 48
That device may shut down one of those processing cards 49 49
to prevent the entire system from overheating. 50 50
That's what I mean by load shedding. 51 51
Now, when a device runs at excessive temperatures 52 52
for too long, 53 53
the performance will decrease on that device 54 54
and the lifespan will decline on that device as well. 55 55
Over time, that device can even suffer 56 56
a catastrophic failure from overheating. 57 57
Our second sensor measurement we need to talk about 58 58
is CPU usage or utilization on the device. 59 59
At their core, 60 60
routers, switches, and firewalls 61 61
are just specialized computers. 62 62
When these devices are running under normal conditions, 63 63
their CPU or central processing unit 64 64
should have minimal utilization 65 65
somewhere in the range of 5 to 40%. 66 66
But if the devices begin to become extremely busy 67 67
or receive too many packets from its neighboring devices, 68 68
the CPU utilization can become over-utilized 69 69
and the percentage will increase. 70 70
Now, if the CPU utilization gets too high, 71 71
the device could become unable to process any more requests 72 72
and it'll start to drop packets 73 73
or the entire connection could fail. 74 74
Usually, when you see a high processor utilization rate, 75 75
this is an indication of a misconfigured network 76 76
or a network under attack. 77 77
If the network is misconfigured, 78 78
for example, let's say you have a switch 79 79
that's misconfigured, 80 80
you can end up having a broadcast storm that occurs, 81 81
and that's going to create 82 82
an excessive amount of broadcast traffic 83 83
that'll cause the switch's CPU to become utilized 84 84
as it tries to process all those requests. 85 85
Similarly, if you have a lot of complex 86 86
and intricate ACLs on your router, 87 87
and then people started sending a lot of inbound traffic, 88 88
that router has to go through all of those ACLs each time 89 89
for that traffic and that can make it become unresponsive 90 90
due to high CPU usage. 91 91
As an administrator, 92 92
you need to monitor the CPU utilization 93 93
in your network devices 94 94
to determine if they're operating properly, 95 95
if they're misconfigured, 96 96
or if they're under attack. 97 97
The third sensor measurement we use 98 98
is memory utilization for the device. 99 99
Similar to high CPU utilization, 100 100
high memory utilization can be indicative 101 101
of a larger problem in your network. 102 102
If your devices begin to use too much memory, 103 103
this can lead to system hangs, processor crashes, 104 104
and other undesirable behavior. 105 105
To help protect against this, 106 106
you should have minor, severe, 107 107
and critical memory threshold warnings 108 108
set up in your devices 109 109
and reporting back to your centralized monitoring dashboard 110 110
using SNMP. 111 111
As a baseline, 112 112
your never devices should operate 113 113
at around 40% memory utilization 114 114
under normal working conditions. 115 115
During busier times, 116 116
you may see this rise up to 60 to 70%, 117 117
and during peak times it may be up to 80%, 118 118
but if you're constantly seeing memory utilization 119 119
above 80%, 120 120
you may need to install a larger 121 121
or more powerful device for your network, 122 122
or you could be under an attack 123 123
for an excessive amount of time 124 124
that's causing excessive loading. 125 125
As you begin to operate your networks in the real world, 126 126
you're going to begin to see what normal looks like 127 127
for your particular network. 128 128
As you see temperatures rising 129 129
or CPU and memory utilizations increase, 130 130
this can trigger alarms in the network configuration 131 131
or a network performance issue is happening right now. 132 132
Then you need to investigate the root cause of that 133 133
and solve those issues 134 134
by bringing those metrics back to a normal level 135 135
within your baseline. 136 136
(upbeat music)