How to detect delayed ACKs/Nagling with Wireshark?

To detect delayed a delayed ACK, you would have to look closely at the pcap file, or each transfer in Wireshark. You will have to look for 200ms delay of the ACK packet at the end of a transfer segment. You'd have to figure out the exact sequence number of the packet.

It is easiest if there is not much traffic on the network, and sending/dissecting a single packet. That way you can see if there is a 200ms delay of the ACK for that particular packet. (It also works with a sequence with odd number of packets sent, again, look for 200ms delay in the ACK for the last packet of a transfer).

You have to look at the last packet in a transfer, preferably with odd number of packets, and see 200ms delay in the ACK for that same packet.

Also, keep in mind that ACKs are cumulative, i.e. they acknowledge receipt of all previous packets in a sequence, not only that particular one.

To disable Nagling/delayed ACKs, check out the TCP Optimizer, or/and our gaming tweaks article.