If you have ever had to analyze a TCP connection, you have definitely seen a three-way handshake. In that handshake, both TCP stacks will exchange the options they are open to use for the connection. In the options field, you may also see several instances of the No-Operation value.
How does this value work? What does it mean (other than no-operation of course), and how should I interpret it?
I have been presenting, training, creating videos, articles and sharing information for over 20 years. As technology evolves, I have tried to keep up by creating lovemytool google and linkedin groups as well as contributing to many social media technical groups/online publications.
When youtube started becoming a source of information for technicians, i created a channel. My youtube channel has over 330 videos covering various topics such as Microsoft operating system, Cisco, Wireless, Wireshark and other technical topics.
I will not be teaching or presenting this year (so far) so i thought i would take some of the suggestions sent to me last year. I had several requests to create some online material so I created a "Wireshark 2 Fundamentals" class on Udemy as my first attempt. This is introductory class for those who want to start using Wireshark or if you need a refresher.
No need to be intimidated by Wireshark! Many IT analysts avoid getting into Wireshark because it seems overwhelming. You don't need a lot of experience to get up and running with Wireshark. In this course you will learn all the basics required to confidently capture, save and navigate around Wireshark's environment. I will spend some time explaining enough of the software to encourage you to use it more.
There are many scenarios with packet slicing is helpful and possible necessary. I covered this in a previous article Network Protocol Analysis Tip: Packet Slicing (http://tinyurl.com/yb38lw9j).
To summarize, here are some examples or scenarios where you should consider packet slicing:
The data is not useful or unreadable/encrypted
To conserve disk space or reduce your trace file size
Legal issues around the payload of captured packets
Reduce load on your capture device. Some packet capture tools are less likely to drop packets when packets are sliced.
David K, one of my YouTube subscribers, asked a great question, “… How could one do that? …”. I thought what a great question since there are times when I assume the reader knows how to do this.
In this video I cover how to figure out the packet slicing value for a HTTP GET command and the destination MAC address. From these two examples, the reader should be able to calculate any other packet slice value.
Please keep in mind that you should always go through this process to determine the packet slice value or offset. This offset may change depending on the network or application so don’t assume the packet slice value will remain the same.
There is a big difference between the Maximum Transmission Unit (MTU) on an ethernet connection or IP interface and the Maximum Segment Size in TCP. In this video we will take a look at how and where each is set, how it impacts the encompassed data, and how the network can adjust these settings.
These core concepts will help when troubleshooting broken or slow connections due to MTU or MSS.
When I first started my website I had a whole section on product ‘issues’ or ‘bugs’.
My intent was to help my clients, subscribers, while reducing the number of emails I get about these issues. Over the years, I found it to be too much work to maintain since I introduced more tools to my website.
In the past 2 years, I have eliminated almost all vendor specific tool webpages from my site that contained tips, tricks and bugs.
Wireshark is still one of the primary tools I use in the field and still do private training or presentations with it, so I thought I would keep that section on my website.
In this video I explain an issue I ran into recently with the default capture interface setting. The purpose of the video is to document the issue and help anyone who may encounter this issue.
Let me know if you find this helpful and I will create more along with my usual tips and tricks.
In this video we will look at the window scale option in TCP. How does this feature improve performance across high-bandwidth, high-latency connections? How does Wireshark come up with the Calculated Window Size field? How can we set the scale factor if we missed the handshake?
We'll answer all of these questions and more in this nine minute video.