Jun 13, 2007 · Subject: [Wireshark-users] TCP Dup Ack I have a couple of customers that have been complaining of issues on their circuits, an issue that causes them to have problems with large file transfers. The only noteworthy problems in their data streams seem to be TCP Dup Acks – I’ve seen as many as sixty, or over a hundred, in file transfers of 100
I think I figured out why the Dup ACK is happening but a soln. has to be well tested. Here is the explanation; "tcp_recved()" is called on receipt of a packet (in TCP_EVENT_RECV) which sets the TF_DELAY_ACK flag on the pcb through "tcp_ack()". The server is expecting a packet with Seq=3781 (conveyed by the ACK in packet 12), but the next client packet has Seq=4329. Packet 15 was expected to arrive before packet 13 but did not. They likely took different paths, or were influenced by queues. 14 0.039982 server TCP [TCP Dup ACK 12#1] 36146 > 8252 [ACK] Seq=1 Ack=3781 Win=32767 Len=0 Apr 24, 2020 · 31350 16:16:12.005045 xxx.xxx.xxx.xxx 192.168.1.2 TCP 66 [TCP Dup ACK 31341#5] 65491 → 3050 [ACK] Seq=14013 Ack=152457 Win=8192 Len=0 SLE=153817 SRE=160617 31351 16 The ACK is getting dropped after the initial SYN, SYN-ACK. Here we are able to see the retransmitted packet is the ACK packet. Also the counter is matching the time of the issue:May 18 01:53:49 2016 nsconmsg -K /var/nslog/newnslog -g tcp_cur_SW reltime:mili second between two records Wed May 18 01:53:07 2016 The problem that we are experiencing is that a network capture performed on the switch using port mirroring of the TMG ports in question reports quite a few of the following errors: previous segment lost, tcp out of order, dup ack, tcp acked lost segment, …
今回は、TCP Retransmit と DupACK と Fast Retransmit の紹介を行います。いずれも、パケットロスといったネットワークの性能が出ない時に出現するキーワードです。 【TCP Retransmit】Retransmit とは”再送”を意味する英単語です。TCPでは、TCPデータの送信者が、受信者からACKを受け取れなかった場合、TCP
The server is expecting a packet with Seq=3781 (conveyed by the ACK in packet 12), but the next client packet has Seq=4329. Packet 15 was expected to arrive before packet 13 but did not. They likely took different paths, or were influenced by queues. 14 0.039982 server TCP [TCP Dup ACK 12#1] 36146 > 8252 [ACK] Seq=1 Ack=3781 Win=32767 Len=0 Apr 24, 2020 · 31350 16:16:12.005045 xxx.xxx.xxx.xxx 192.168.1.2 TCP 66 [TCP Dup ACK 31341#5] 65491 → 3050 [ACK] Seq=14013 Ack=152457 Win=8192 Len=0 SLE=153817 SRE=160617 31351 16 The ACK is getting dropped after the initial SYN, SYN-ACK. Here we are able to see the retransmitted packet is the ACK packet. Also the counter is matching the time of the issue:May 18 01:53:49 2016 nsconmsg -K /var/nslog/newnslog -g tcp_cur_SW reltime:mili second between two records Wed May 18 01:53:07 2016
The Dup-ACK from server in step(4) is caused by the Seq 28 in step(3):. 65509 > distinct [RST] Seq=28 Win=0 Len=0 Because server is expecting Seq#25 but received #28. This happens when seq 25~27 is lost in the network.
Oct 26, 2016 · Match found — if the SequenceNumber and AcknowledgementNumber are identical to those in the last segment evaluation, the payload count value is equal to “pyl.Count”, and the source and destination address are the same as the last segment evaluation, then the message is a TCP retransmit; in which case, the variable “mnretrans” is set to the retransmit message number which is returned Remember that duplicate ACKs are normal in many situations. Nothing guarantees packets will be received in the order they are sent, and even one packet out of order can produce a duplicate ACK. Again, look for actual retransmissions. You should see a fast retransmit after 3 consecutive duplicate ACKs on most systems. 80 → 62765 [ACK] Seq=16061 Ack=1192 Win=17520 Len=1460 [TCP segment of a reassembled PDU] 34: 7.382573: 166.102.136.11: [TCP Dup ACK 192#1] 62772 → 80 [ACK Feb 15, 2017 · TCP provides reliable, ordered, and error-free transmission. To do so TCP has features such as Handshake, Reset, Fin, Ack, Push packets, and other types of flags to keep the connection alive and to not lose any information. TCP is used under a number of application protocols, such as HTTP, so it is important to know how to diagnostic TCP issues.