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How does Wireshark knows that a packet on the receiver side is being retransmitted. I mean it makes sense on the sender side: Wireshark sees two identical packets (with the same sequence number) being sent, and so it will mark the second packet as being retransmitted.

Note that I am not talking about two identical packets being received and TCP will ignore one of them. What I talking about is when I have only one packet received and Wireshark has marked it as being retransmitted. Is it because for example I receive packet 1 and then I receive packet 3, and then when packet 2 arrive, Wireshark will assume that packet 2 is being retransmitted?

asked 27 Jul '15, 08:37

John_857's gravatar image

John_857
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Wireshark makes an educated guess, based on the delta time of the "old" packet arriving relative to the packet loss - if it is following the gap really quick it's marked out of order, otherwise it's called a retransmission.

A retransmission can never be sent before the receiver has notified the sender about the missing segment(s), so a true retransmission cannot arrive earlier than the round trip time. Exceptions are when the sending stack is going crazy for whatever reason, sending retransmissions way too fast.

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answered 27 Jul '15, 10:01

Jasper's gravatar image

Jasper ♦♦
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edited 27 Jul '15, 10:03

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question asked: 27 Jul '15, 08:37

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last updated: 27 Jul '15, 10:03

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