101 posts categorized "Chris Greer" Feed

How TCP Works - No-Operation (by Chris Greer)

Hey packet people! 

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? 

Get the answers to these questions here:


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How TCP Works - MTU vs MSS (by Chris Greer)

Hey packet people! 

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. 

Hope it helps in troubleshooting with Wireshark! 

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How TCP Works - Window Scaling

Hello packet-heads! 

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. 


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Hey Network Engineers - What To Do While Everyone Is Away (by Chris Greer)

Empty office Wireshark

You drew the short straw.

Over the next couple of weeks, while everyone else is skiing in some amazing place or finally taking that year-end time with their kids, you are left behind at the office to “monitor” the system.

Unless you work for UPS or Amazon, it will most likely be a relaxed couple of weeks! It will be tempting to kick back and watch YouTube, or act busy while doing some other mundane chore.

However, the last two weeks of the year is also a great time to be a network engineer. Here is a list of things you can work on while everyone else is away.

  1. Throughput Testing

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How TCP Works - The Receive Window (by Chris Greer)

What does that Window field in the TCP header do? 

Many people ask this question after capturing a trace file with Wireshark. What is the TCP Window? How does it work? How can I use it to troubleshoot performance problems? 

We will answer these questions and more in this nine minute video. Check it out! 

Note: This video focuses on the TCP Receive window. We will cover the send window in another video. 


Author Profile - Chris Greer is a Network Analyst for Packet Pioneer LLC and a Certified Wireshark Network Analyst. Chris regularly assists companies in tracking down the source of network and application performance problems using a variety of protocol analysis and monitoring tools including Wireshark. Chris also delivers training and develops technical content for several analysis vendors. Got network problems? Let's get in touch

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Intro to Wireshark – Sharkweek Teaser! (by Chris Greer)

Does opening a packet trace stress you out?

If so, you aren’t alone. Packet analysis is tedious, detailed, and can be very time consuming. Usually captures are taken to troubleshoot issues when the stakes are high and failure to find the problem is not an option. You may even have your boss breathing down your neck, expecting you to miraculously see the smoking gun in a matter of minutes, leaving you to wonder if your job is on the line.

Hey, we’ve all been there.

Packet analysis with Wireshark is an art form that can take a long time to develop. Gaining comfort with trace files starts with some basic steps that can go a long way in helping you find the culprit of your performance or security problem. Here, we will take a look at a couple quick hints that all new Wireshark users should know – but we will definitely leave some for the Intro to Wireshark session at Viavi Sharkweek starting on Monday, November 6th. Register here! https://observer.viavisolutions.com/wireshark-week/

Step 1.

Know the packet path and capture well.

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