Basic Network Troubleshooting using Wireshark


language: EN

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package. Yeah. Danin, I can see you are there. How about him? Okay, I saw you are
here. So, okay, let me try to help you to extract this. Okay, from here. All right,
that's the file that we are going to use during the training. Okay, so back to here. Okay,
let's go back to the slideshare. Okay, so now you have those files, right? Let's go
ahead and get to it. All right, I think before that, I will give you some brief
about the network troubleshooting. So maybe I want to hear about some feedback from your
side as well, because at least I will have a brief understanding on what you are doing
and what is your level and then how can I help you to understand the basic knowledge
of the Wireshark. Okay, so network troubleshooting actually for my role. I'm not really like using
the command line to Linux, but I'm mostly using Windows for network troubleshooting.
And why do I need it? Because, for example, okay, let me give you an example. Sometimes,
let's say I want to transfer money while the online banking app. So when I log in to the
app, so when I select my front account and to account, let's say, I fill in all the
information needed. When I click transfer, that's a very important process, right? Because this
money transfer process. But sometimes I can see the spinning wheel is keep loading.
Or sometimes I will see like, why no response from the maybe banking side? And suddenly
prompt, oops, the transaction fell. Okay. And then I'm the client, I'm so worried about
now where my money go on. Is that fail? But then my money was deducted from that account.
So what should I do? So normally, if I'm the one who encountered this failure, or I'm receiving
some feedback or complaint from the client, I would try to use a browser. Okay, let me show you.
Okay, so let me go to the, all right. So let's say this is the website. So if I click something
here, okay, so let me open the inspector and network. All right. If I simply type any keyword
I press enter. So you can see there are a lot of information under the tab. So I will always
monitoring the transaction here. So if I see there's an API call, clients send a request to
the server side. So I will see like, for example, this one. So I will try to click on it
and I will see the response and the payload as well, payload and also the response from the
server. Sometimes the server will just return the 200, but some server, I think most of
the server response were passing the content as well. So if let's say, okay, I'm not
able to capture any failure. I cannot get any clues from the network or just a very
brief information for me. It's not enough. So I will use some tools. I will use some
command line. I will also go to the Azure portal to check the Azure configuration as well.
So that's what I did. But then for the network engineering, I think what you're familiar
is that. So, okay, later on I will show you, but let's see what is the network troubleshooting.
So this is the process of identifying the problem and then do some analysis,
analyze the logs, analyze all the capture packets, analyze any information that you
collect from the website, from the browser, from the network analyzer tools and
resolving the issues that affect the performance, connectivity or functionality of the network.
And then, so why is it important? Because I think right now, now always everyone is
using network, right? No matter what. And now AI is very popular. So whenever we have any
questions, we will sometimes, I mostly will ask chat GBT, Gemini or any like co-pilot
tools for whatever purpose. So we are using network in every day, even in every minute.
So it's very critical for communication and data access. And so let's say our client
got some downtime or issues and affect their productivity, business operations or security.
So it's very, very serious issue is a very, very critical problem and matter. So it will help
it will cause our company to lose the money and the business. Right. And then so we need
to like be proactive to do some troubleshooting to help to prevent the long-term issues.
And what is the common network issues that we are always encountering?
Okay. For example, okay. So I will use some example, why inability to connect to the
internet or local network. So this was happened if the Wi-Fi drop, but then is it always
happened? Not really. But it will happen mostly in my case is that when I connecting
to the virtual machine or if my client is using the virtual desktop and for their,
maybe for their assessing like connection to the application that we develop. So
sometimes it will happen. And it's not only like internet drop due to the firewall policy.
Sometimes it will always do to the slow network speed as well. Okay. So specific websites,
not accessible, DNS error or device unable to communicate is always happen.
If yeah, if the connection or internet got some like latency issue, or maybe the firewall
will drop or maybe the server site has no accessible like got this 404 or 500 error.
Okay. This was sometimes happened in my daily tasks. So that's why,
that's why sometimes we use some tools to do at least some first ground of the troubleshooting.
So I think that tools, the common line, I believe Ham and Tanin will be familiar with,
right? Are you guys familiar with the common line tools and using it in your daily tasks?
Okay. So what is the normally, what is the OS platform that you use? Is it Linux or Windows
or Windows? Okay. Then how about the tools that I showed you guys before, the network tab
in the browser, the developer tool. Have you guys ever used the developer tool in any browser
like do some troubleshooting or debugging here? No. Okay. So all right. I think it's cool
because we have a different background, but I think that was reacted because if we send the
request from client side to response, that's one of the way that I monitor the transaction in
here. Okay. All right. So, okay. Back to here. So I think ping, everyone is familiar, right? So
this is to test. We send the ICMP packets to test if a device is reachable
and we can measure the response time. And then trust rock. So this is the comment
which shows each hub between the source and the destination to identify where delays or
drops happen can. All right. So for the IV config slash all, this is to view the IP settings
to display and configure network interfaces. And then NS lookup. Okay. We, for example,
if you want to get the IP address, so we will check if the DNS query is resolved correctly.
And then wild shark, I think this is our main purpose today. We are going to use a wild shark
to capture and analyze the packets deeply. But I think in this training, I will don't
spend too much time on the troubleshooting, but I will drive it to the basic usage of the
wild shark. Okay. So next state and TCP dump. All right. Okay. So troubleshooting methodologies,
I think this is quite similar, no matter who you are. So it's either you are an engineer,
any, and never engineer or QA engineer or developer. So first of all, whenever we
encounter any issues, right? Okay. Let's say crank comprend, the performance of the
application is low. So they can see, or they are not able to upload a map file to their website,
or they are not able to upload the file or download file to their machine. So we will try
to collect what is the problem in a very high level. And we will try to collect all those
steps. And we will see, is it possible to collect those logs or reports or any symptoms? Okay.
Understand when, where, and how often the issue occurs. Is it always reproducible or only
happen in their particular machine or environment or windows or what is the browser type they
Okay. So second, based on the symptoms or initial log, we are trying to, you know,
like form a hypothesis. Okay. Is the device receiving a valid IP or is DNS resolution failing
or is the wifi signal weak or could a cable report be faulty? So we are trying to get
possible causes. So for me, I will usually like form a hypothesis like maybe the
connection in between server and client is not stable. So I would at least try to
reproduce in my local machine. If my local machine is also encountered that issue,
that means I don't need to collect all those information from client side,
but it's only happened in their side. I will try to understand. Yeah. I want to try to collect
all those needed logs. Okay. And then isolate the codes. So what does that mean? Okay. This
is important to narrow down the source, like try to connecting another device on the same
network and use the tools like ping, ipconfig or our short to compare the healthy versus
a faulty system. So do a comparison and check logs from router or firewalls.
And then once you are able to get some clues, so we will try to implement a solution,
maybe, okay, let's say restart the routers or switches or reassign the IP address
or if the hardware issue or cable issue, we can repress or change it
or adjust the file rules or DNS setting. All right. And then verify the solution. We need
to make sure is the issue has been resolved. Can the user access to the internet? Is the
performance back to normal or are the services responding properly? And then the final one is
document and prevent future issues. So this is very important because we need to record what
happened and how it will fix, what is the root cause and what are the lessons learned.
So we can implement monitoring tool or alerts or plan for redundancy or improve the
Okay. So that is the basic ideas of the troubleshooting.
So I won't go into the deeper level for this, but I will jump into our Wireshark lesson now.
All right. Okay. So I think first,
so let's just talk about why you are here in the first place. So I think since you are using
Wireshark tool every day, right? So Wireshark can be intimidating. So when you are looking
at the network traffic, it doesn't really matter what you are looking at. It could be
or maybe even you are using Wireshark to investigate the cyber security incident.
But when you trigger the Wireshark, for example, let me open it.
So you can see the packets keep increasing, right? So it's intimidating. So it's very
capture to analyze all those information with the 6,000 records here. Okay.
So when you are looking at the network traffic, it doesn't really matter what
you are looking at. It could be troubleshooting network problem, right? Like what I said,
could be a cyber security incident. So we capture a lot on the wire, but there's
a lot whipping by like few thousand, 6,000 within just maybe 10 seconds. So it's easy
to get overwhelmed. So even with a simple screen as like you see just now. Okay. So
here's a lot going on. What the protocols matter and what filter do I set and what
I really hone in to find the source of the problem and even get the proof of what happened
during an attack. Okay. So before we jump into the course, I want you to open the pre lab.
So right now we are here to do in this course to make Wireshark more accessible to you as a
tool in a toolbox that can help you to troubleshoot and investigate incident faster.
All right. So later on, I will need your help to open the pre lab. Let me show you.

on 2025-04-22

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