In this video, we're going to discuss
how to troubleshoot network performance issues
that you may experience out in the field.
Now, the five most common causes
of network performance issues
are high CPU usage in a network device,
high bandwidth usage in a network,
poor physical connectivity, malfunctioning of your network,
or DNS problems.
First, it's important to realize that every network device,
such as your routers, switches, and firewalls,
are, at their core, a computer,
that includes a CPU, or central processing unit.
If that device begins to experience
a high CPU utilization rate,
that device is going to start slowing down,
and in turn, the network that is being processed
for all of those packets is also going to slow down.
So whenever a CPU is overutilized,
latency, jitter and packet loss will start to increase,
and this can cause the entire network performance
to deteriorate on you.
So to solve this issue,
you need to either upgrade your network devices
to more powerful ones,
such as enterprise-class routers and firewalls,
or you need to simplify the processing load
that you're putting on those devices.
For example, I once saw an enterprise network
where their border firewall
was slowing down the entire network.
Now, when we looked at it closer,
we saw their access list had over 3000 entries in it.
That meant that every time a packet was received,
it was checked against these 3000 individual entries
to find its match or to eventually block that packet.
Now this consumes a lot of processing time
and leads to high CPU utilization rates.
Now, we conducted an ACL review
and we were able to simplify their rule set
down to about 300 rules.
This drastically reduced the CPU utilization rate they had
and sped up the network.
Second, high bandwidth utilization
is another cause of network performance deterioration.
Now, when bandwidth utilization is high,
network communications have to wait to enter
or leave that network.
This can cause buffers to fill up,
and in the worst cases, packets can be dropped.
Now when those packets are dropped,
they're going to be retransmitted if they were sent using TCP,
and this leads again
to even higher bandwidth utilization rates
because we have retransmissions.
To solve this issue,
you can either increase your bandwidth size
by paying more to your internet service provider,
or you can do a network flow analysis
and determine what sites and traffic types
are being used by all of your clients.
For example, if 90% of your traffic
is being wasted by people scrolling Facebook each day,
you may need to change your acceptable use policy
or reduce or eliminate when people are allowed
to use Facebook on your network.
Literally, I had one network where 90% of our traffic
was either going to or coming from Facebook,
and our end users kept complaining
because they couldn't do any real work on their job
because our internet was so slow.
And this is why conducting a netflow analysis
can really help you understand
what your users are really doing on your network
and is it something you want to allow?
Third, you may have network performance issues
if you have a poor physical connection.
To solve this, you're going to need to check your cables
and test them one by one.
Now, if you suspect it's an issue
with the internet service provider's portion of the network,
you need to connect a test client
directly to the demarcation point
and test the connection from there.
If that connection is poor,
then you know it's your ISP's problem to solve.
If it isn't, that means it's something in your network
that's a problem,
and you need to start testing every cable
from the demarc point
all the way back to your border router
and then to your switch, and then to your client,
until you find where that broken or damaged cable might be
that's causing this slowdown in your network connection.
Remember, a damaged cable may still operate,
but it's going to cause additional errors,
and these errors require data to be retransmitted
over and over again,
and this slows down your overall network performance.
To test your cables,
always use a cable tester for twisted pair connections
or a fiber light meter for fiber optic connections.
Fourth, we have malfunctioning of our network.
Now, if you have misconfigurations of your devices
or hardware failures,
your network performance is obviously going to suffer.
Sometimes this can even be caused
by using old or outdated network operating systems.
Again, this is an area
where your seven-step troubleshooting method
is going to help you identify
the exact location of the device
that's having these issues,
and then you can focus on whether it's a configuration issue
or a hardware failure issue
that's causing those network performance issues.
Finally, fifth, we have DNS problems in our network.
DNS issues are a serious cause
of a lot of our network performance issues.
Remember, if you have a high DNS latency,
this is going to slow down the overall user experience
because when that user requests a website,
they first have to go and resolve that domain name
all the way out to that DNS server
and get the IP address over DNS.