Wireshark tshark Capture With Examples

Before I get into the tshark command syntax and other details, I want to chat about why you want to use tshark or any command line tool. Simply put, working from the command line allows a tremendous amount of consistency and flexibility.

Consistency

When you try to have someone perform your capture using the Wireshark GUI, there are many opportunities for errors and its just very time consuming. When you have the command line syntax figured out, you can put it in an email, batch file or document ensuring the client is doing exactly what you wanted. The added bonus is that working from, the command line is usually more responsive that remotely controlling a GUI over possibly slow links.

Flexibility

As I mentioned earlier, using the command line allows you to put the command in a batch file or document. This is incredibly useful if you wanted to schedule a capture, or if you wanted to configure a computer to automatically start capturing when it’s turned on. Other examples would be setting a desktop shortcut for the client to start a capture or kicking off a capture from a monitoring system that allows you to run a batch file when an error occurs.

In this video I will cover some of the common command line capture scenarios as well as determining what your index is and testing your commands.

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Don’t assume anything when troubleshooting! (John Modlin)

I was working at a large network heterogeneous environment and started working on a problem of scanners at field offices being unable to transfer documents across the WAN. Working on this problem led me quite down the rabbit hole, a black hole to be more specific.


The field techs had already changed out scanners, but the site continued to be intermittently unable to send documents across the WAN. Some documents transferred, some didn’t. After checking permissions and general settings on the scanner, I started looking at the network path.

Wireshark Interfaces and File List Tip

 Networkdatapedia.com has been asking for material that focus on knowing your network and/or knowing your tools.

Sounds pretty simple but trust me this is anything but simple or obvious. When you use the same tool and it becomes your ‘favorite’ or ‘go to tool’ you might be resistant to trying new tools.

Great example is back in the early 90’s when I was using Network General Sniffer products. I was getting very comfortable with it and was actually solving issues with no training. Through the years I heard of Lanalyzer, Capsa, Cinco, NetXRAY, Observer, Microsoft Network monitor, Protocol Inspector and of course Ethereal (aka Wireshark) as well as ton, I’ve probably forgotten.

I remember showing my Sniffer sales person Microsoft Network Analyzer and Ethereal explaining some if the features I liked. His response is “don’t waste your time on that free stuff”, followed up with “how good can it possibly be when its free”.

I soon figured out that every tool has its pluses and minuses and figuring out what works best for you is the toughest part. When you find that tool that you always reach for first, you need to take the time to learn all the nuances and what features new versions may bring – or break ;)

In this video I spend a few minutes showing you how to clear your ‘most recently used file list’ and how to hide network interfaces you won’t be using. Its important to note that hiding the interfaces does not delete, disable or affect them directly.

For example, if you hide your WiFi adapter in Wireshark, you can still use it to surf, ping, etc.. it will just be hidden from the available adapter list in Wireshark.

Enjoy.

Determining ARP Refresh Rate With Wireshark

 

There have been more than a few times where I had to illustrate that ARP was an issue.

When a suspected ARP issue, or you just need to understand how often a device ARP’s, or you need a good challenge when using your favorite packet analyzer, this is a great exercise.

DNS Client Issues

 In this video I wanted to show you an issue that I encounter quite often. DNS is one of those protocols we all take for granted and most people believe that if its working, you can’t do much to tune it.

There are many things you can do to improve DNS performance. One of the more common techniques is to configure a device as a local DNS server, cache or relay for those scenarios where you might have slow internet connections.

I want to focus on the client configuration. I’ve seen DNS server entries (manual or DHCP assigned) that are problematic. For example, DNS servers that no longer exist, typos, slow DNS servers or DNS servers that are located on slow links or paths.In this case I highlighted what your packet trace will look like when you attempt to use a device as a DNS server that is not a DNS server. I also explain why the ICMP packets are important in this process.

Big take away is to review your DNS or any name server configurations every so often to ensure there isn’t any issues.

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