I have a NAS that is running slow, has been. When I run Wireshark while opening a file on that appliance I am seeing lots and lots of the examples below. (To me it looks like way to many)
90[TCP Dup ACK 8796#16] 6873>microsoft-ds [ACK] seq=27065 Ack=8756344 Win=1619 Len=0 SRE=8824884 SLE=88161
1514 [TCP segment of a reasembled PDU]
asked 21 Mar '13, 11:14
Hard to tell without more details, but Dup ACKs are acknowledgements that were repeated (in this example 16 times, so a total of 17 identical acknowledges). This is usually a sign of either lost packets or impatient receiving nodes. Problem with NAS captures is that they get pretty big, but you could try to look for packet loss, retransmissions or zero window problems. There is a combo filter that will show you issues like that: tcp.analysis.flags.
answered 21 Mar '13, 11:28
Duplicate acknowledgements gets triggered when there is a packet loss. It is the client/receiver's way of notifying the server/sender that "hey i some how lost a segment can you please retransmit again"In normal case server pay attention to these duplicate acks and sends a retransmission to the client. You can set the display filter as tcp.analysis.flags to dig further.
answered 21 Mar '13, 11:26
As @Jasper is saying, it looks like there is indeed a bit of packet loss in your network. Assuming you are running this NAS in a local network, I can imagine 2 issues that might be causing the packet loss and therefor the slow transfer speeds:
answered 21 Mar '13, 13:14