Diagnosing MTU Black Holes: Using Ping and Wireshark to Find Fragmentation Issues on a WAN (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 Tips: How to Hide Unused Network Interfaces and Clear Your Recent File List

 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.

How to Determine ARP Refresh Rate Using Wireshark (Windows 8/10 Guide)

 

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.

Troubleshooting DNS Client Configuration Issues: How to Spot Bad DNS Servers in a Packet Trace

In this video I wanted to show you an issue that I encounter quite often that is not specifically related to DNS. DNS is one of those protocols we all take for granted and most people believe that if its working, and no one is complaining, go find something else to do.

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/high latency internet connections.

Slice It Smart: Extend Your Capture Time With Packet Slicing

I would say packet slicing is one of the most critical techniques to understand.

Back in the day when we had hard drives with limited disk space and we needed to capture for long periods of time, we used packet slicing.

Packet slicing in Wireshark is one of those features that doesn’t get much love, but once you use it, you wonder how you ever captured packets without it. The basic idea is simple: instead of grabbing the entire packet payload, you only capture the first N bytes. For many troubleshooting and analysis tasks, that’s more than enough to see headers, flags, and protocol behavior without hauling around a ton of unnecessary data.