Duplicate ACKs and fast retransmissions
Another phenomenon that you will see in TCP is what is called duplicate ACKs and fast retransmissions. This phenomenon also happens due to performance problems, and in this recipe we will focus on how to find them and what they indicate.
Getting ready
When you see that the network becomes slow, one of the reasons for this can be duplicate ACKs. Connect the Wireshark in the port mirror to the suspicious client or server and see the results.
How to do it...
In most cases, duplicate ACKs will happen because of high latency, delayed variations, or a slow end point that simply does not response to ACK requests.
When looking for a reason for slow communication, duplicate ACKs can be one of the reasons for it.
When you see a reasonable amount of duplicate ACKs, that is, 1 or 2 percent, this is probably not your problem.
When you see a huge number of duplicate ACKs (say ten of them), you might have:
A very busy communication line that causes variations in delays
A...
