Weired TCP retransmission [closed]
My question is why a TCP flow make a re-transmission when a network has enough link bandwidth.
For finding a cause, I used a wireshark. I got the below captured at a host side (10.0.0.1)
25434 50.968633785 10.0.0.1 10.0.0.2 TCP 33370 42848 → 50004 [ACK] Seq=14063654 Ack=1 Win=29696 Len=33304 TSval=290016 TSecr=290011
25435 50.968637512 10.0.0.1 10.0.0.2 TCP 31274 42848 → 50004 [PSH, ACK] Seq=14096958 Ack=1 Win=29696 Len=31208 TSval=290016 TSecr=290011
25492 50.977183364 10.0.0.1 10.0.0.2 TCP 866 [TCP Retransmission] 42848 → 50004 [PSH, ACK] Seq=14127366 Ack=1 Win=29696 Len=800 TSval=290019 TSecr=290011
25513 50.979382486 10.0.0.2 10.0.0.1 TCP 66 50004 → 42848 [ACK] Seq=1 Ack=14096958 Win=16776192 Len=0 TSval=290018 TSecr=290016
25514 50.979383087 10.0.0.2 10.0.0.1 TCP 66 50004 → 42848 [ACK] Seq=1 Ack=14128166 Win=16776192 Len=0 TSval=290018 TSecr=290016
25543 50.981453868 10.0.0.2 10.0.0.1 TCP 78 [TCP Dup ACK 25514#1] 50004 → 42848 [ACK] Seq=1 Ack=14128166 Win=16776192 Len=0 TSval=290019 TSecr=290019 SLE=14127366 SRE=14128166
In summary,
(1) [.1 -> .2 ] SEQ = 14063654, ACK = 1, LEN = 33304
(2) [.1 -> .2 ] SEQ = 14096958, ACK = 1, LEN = 31208
(3) [.1 -> .2 ][Retr] SEQ = 14127366, ACK = 1, LEN = 800
(4) [.2 -> .1 ] SEQ = 1, ACK = 14096958, LEN = 0
(5) [.2 -> .1 ] SEQ = 1, ACK = 14128166, LEN = 0
(6) [.2 -> .1 ] SEQ = 1, ACK = 14128166, LEN = 0, SLE =14127366, SRE=14128166
I totally do not know why the re-transmission occur at (3)
I guess the SACK (6) occur due to (3).
As you see, (4), (5) is the ack due to (1), (2) respectively.
I think the re-transmission (3) is not needed.
Could you give me a little hint about the reason of the re-transmission?
Thank you so much and sorry for re-uploading.
Closed for the following reason "duplicate question" by nimdrak 2019-08-28 14:23:17 +0000
Comments
Is this is another capture related to the question you asked, and got some help with over here? If so, then this question should be closed, the original re-opened and your additional info appended to the original question to keep all the discussion together.
@grahamb I did! Thank you for your comment!
@grahamb although I closed this question, I cannot open the original question due to the lack of points. Could you help me?