The TCP implementation ACKs every other data packet. So you should see, typically, two data packets received and then an ACK sent. The sender, of course, is not waiting for the ACK anyway. It will continue to transmit until the window is full, even in the absence of an ACK.

I'm getting excessive TCP Dup ACK and TCP Fast Retransmission on our network when I transfer files over the MetroEthernet link. The two sites are connected by one sonicwall router, so the sites are only one hop away. Here is a screenshot from wireshark, and here is the entire capture. In this capture, the client is 192.168.2.153 and the server ...

2011年5月6日 · You'll find duplicate ACK's, TCP Retransmits, broadcasts, errant protocols, etc. on every network. You should focus on the volume of duplicate ACK's and the hosts most involved in sending the duplicate ACK's to determine if that's really a symptom of a larger problem or just the natural operation of the network.

2011年2月16日 · Basically, what is happening is that the client's machine is sending the SYN packet to establish the TCP connection and the web server receives it, but does not respond with the SYN/ACK packet. After the client has sent many SYN packets, the server finally responds with a SYN/ACK packet and everything is fine for the remainder of the connection.

2017年2月23日 · So the ACK delay mechanism loses the bet, over and over, delaying the ACK, waiting for a packet on which the ACK can be piggybacked, not getting it, and then sending the ACK, delayed. Nagle Algorithm The Nagle algorithm can be seen as something implemented on the sending side to improve efficiency trying to always send full-sized TCP data packets.

I have just been reading this explanation of TCP sequence & acknowledgment numbers. About half-way down there is this diagram: Near the end of the page, the explanation of the final step, step 4, includes this text: Note that the sequence number of the segment in line 4 is the same as in line 3 because the ACK does not occupy sequence number space.

TCP Retransmits; Duplicate ACK; Segment lost; If you receive a TCP retransmit, this is because the ACK you have sent was not received by the server. The server was not aware the TCP packet was received, thinks it was lost underway and will send it again. The duplicate ACK is typically received at the Sender in the following scenario:

A latency-sensitive application does not want to wait around for TCP's efficiency delays so the application will usually disable them, causing data to be sent as quick as possible with a Push flag set. On Linux, this is done with the setsockopt() flags TCP_QUICKACK and TCP_NODELAY. See man 7 socket for more information.

2014年12月5日 · tcpdump "tcp[tcpflags] & (tcp-syn|tcp-ack) != 0" Check out the tcpdump man page , and pay close attention to the tcpflags. Be sure to also check out the sections in the Wireshark Wiki about capture and display filters.

The client in this case uses nonblocking sockets, so the connect() call will return immediately while the kernel keeps waiting for the SYN,ACK packet from server. Unfortunately the client code was very impatient: if the connection wasn't established after a few hundred milliseconds, the client would call close() on the socket.