In this lesson,
we're going to talk about sensors
that help us monitor the performance of our network devices,
those devices like routers, switches, and firewalls.
Now, these sensors can be used to monitor
the device's temperature, its CPU usage, and its memory,
and these things can be key indicators
of whether a device operating properly
or is about to suffer a catastrophic failure.
Our first sensor measurement we need to talk about
is the temperature of the device.
Now, most network devices,
like your router, switches, and firewalls,
have the ability
to report on the temperature within their chassis.
Now, depending on the model,
there may be only one or two temperature readings,
or on some larger enterprise devices,
you may have a temperature reading
on each and every controller, processor, interface card,
and thing like that inside the system.
Now, the temperature sensors can be used
to measure the air temperature inside the intake outlet
and the air temperature at the exhaust outlet at a minimum.
Now, for each of these sensors,
you can set up minor and major temperature thresholds.
Minor temperature threshold is used to set off an alarm
when a rising temperature is detected
but it hasn't reached dangerous levels yet.
When this occurs, a system message is displayed,
an SNMP notification is sent,
and an environmental alarm can be sounded.
Now, when you have a major temperature threshold,
this is going to be used to set off an alarm
when a temperature reaches dangerous conditions.
At this level, we want to still display those system messages,
get that SNMP notification,
and have the environmental alarm sounded,
but in addition to that,
the device can actually start to load shed
by turning off different functions
to reduce the temperature
being generated by the device's processor.
For example, let's say you have a router
with multiple processing cards in it.
That device may shut down one of those processing cards
to prevent the entire system from overheating.
That's what I mean by load shedding.
Now, when a device runs
at excessive temperatures for too long,
the performance will decrease on that device
and the lifespan will decline on that device as well.
Over time, that device can even suffer
a catastrophic failure from overheating.
Our second sensor measurement we need to talk about
is CPU usage or utilization on the device.
At their core, router, switches, and firewalls
are just specialized computers.
When these devices are running under normal conditions,
their CPU or central processing unit
should have minimal utilization,
somewhere in the range of 5 to 40%,
but if the devices begin to become extremely busy
or receive too many packets from its neighboring devices,
the CPU utilization can become overutilized
and the percentage will increase.
Now, if the CPU utilization gets too high,
the device could become unable to process any more requests,
and it'll start to drop packets,
or the entire connection could fail.
Usually when you see a high processor utilization rate,
this is an indication of a misconfigured network
or a network under attack.
If the network is misconfigured, for example,
let's say you have a switch that's misconfigured,
you can end up having a broadcast storm that occurs,
and that's going to create
an excessive amount of broadcast traffic
that'll cause the switches CPU to become overutilized
as it tries to process all those requests.
Similarly, if you have a lot of complex
and intricate ACLs on your router,
and then people start sending a lot of inbound traffic,
that router has to go through all of those ACLs
each time for that traffic,
and that can make it become unresponsive
due to high CPU usage.
As an administrator, you need to monitor the CPU utilization
in your network devices
to determine if they're operating properly,
if they're misconfigured, or if they're under attack.
The third sensor measurement we use
is memory utilization for the device.
Similar to high CPU utilization,
high memory utilization can be indicative
of a larger problem in your network.
If your devices begin to use too much memory,
this can lead to system hangs, processor crashes,
and other undesirable behavior.
To help protect against this,
you should have minor, severe,
and critical memory threshold warnings
set up in your devices
and reporting back to your centralized monitoring dashboard
using SNMP.
As a baseline, your network devices should operate
at around 40% memory utilization
under normal working conditions.
During busier times, you may see this rise up to 60 to 70%,
and during peak times, it may be up to 80%,
but if you're constantly seeing memory utilization
above 80%,
you may need to install
a larger or more powerful device for your network,
or you could be under an attack
for an excessive amount of time
that's causing excessive loading.
As you begin to operate your networks in the real world,
you're going to begin to see what normal looks like
for your particular network.
As you see temperatures rising,
or CPU and memory utilizations increase,
this can trigger alarms that a network configuration
or a network performance issue is happening right now.
Then you need to investigate the root cause of that
and solve those issues
by bringing those metrics back to a normal level
within your baseline.