Troubleshooting Dropped Connections with TCP DUP ACKs in Wireshark

As network administrators, we often encounter issues with dropped connections that can be frustrating and difficult to resolve. In this article, we will explore how to troubleshoot these problems using Wireshark, focusing on the role of TCP DUP ACKs.

When examining a network issue, it is essential to gather as much information as possible about the problem. In your case, you have provided a snippet from a Wireshark capture that shows an abundance of DUP ACKs (duplicate acknowledgement packets). These packets are sent by the receiving device to acknowledge receipt of data, and their presence can indicate issues with packet loss or delayed transmission.

To better understand what is happening in your network, let's break down the Wireshark capture. In this example, we see that there are many DUP ACKs being sent from 172.16.0.4 to 66.18.111. This suggests that packets may be being lost or delayed in transit between these two devices.

A possible explanation for this issue is a physical layer problem caused by the home-made cables connecting your devices to the switch. It's essential to verify that all connections are secure and functioning correctly, as even minor issues can cause packet loss and delays.

Another potential reason for DUP ACKs is network congestion or high latency. If there is significant traffic on your network, it may be causing packets to be delayed or lost, leading to the need for DUP ACKs. To mitigate this issue, consider implementing Quality of Service (QoS) policies or upgrading your network infrastructure to improve overall performance.

To further troubleshoot this problem, you can try using Wireshark's built-in features, such as filtering and coloring rules, to analyze the capture data more effectively. For example, you can use the 'tcp dup ack' filter to focus on packets that contain DUP ACKs and identify any patterns or trends in their distribution.

In conclusion, when dealing with dropped connections and TCP DUP ACKs in Wireshark, it is crucial to gather as much information as possible about the problem and explore potential causes. By analyzing your capture data, you can identify issues related to packet loss, delayed transmission, or physical layer problems. With this knowledge, you can implement targeted solutions to resolve these problems and improve the overall performance of your network.

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