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TCP - Overlapping Retransmission

Hey folks,

Happy new year 2021. I hope it started well for all of you.

I've found an (for me) unusual behavior in one of the captures in this forum, and I want to ask if anybody can explain me what this behaviour is related to. The behaviour has nothing to do with the issue itself. That's why I started a new question.

The user had an issue with a connection from a client (192.168.0.1) to a web server (10.10.10.1). The TCP handshake was successfull but after some data packets the ACKs from the client seems to be blocked on the way to the server. My question is about the retransmisson in packet #12. It's an retransmission of the last packet from the server (#8), which contained 1144 bytes payload. But due to the sequence number the retransmission packet has been filled up with additional payload of packet #7 to reach the full MSS of 1460 bytes. Is this a expected behavior for any type of TCP functionality? I've never seen this before.

Download Capture

Jas Man

TCP - Overlapping Retransmission

Hey folks,

Happy new year 2021. I hope it started well for all of you.

I've found an (for me) unusual behavior in one of the captures in this forum, and I want to ask if anybody can explain me what this behaviour is related to. The behaviour has nothing to do with the issue itself. That's why I started a new question.

The user had an issue with a connection from a client (192.168.0.1) to a web server (10.10.10.1). The TCP handshake was successfull but after some data packets the ACKs from the client seems to be blocked on the way to the server. My question is about the retransmisson in packet #12. It's an retransmission of the last packet from the server (#8), which contained 1144 bytes payload. But due to the sequence number the retransmission packet has been filled up with additional payload of packet #7 to reach the full MSS of 1460 bytes. Is this a expected behavior for any type of TCP functionality? I've never seen this before.

Download Capture

Jas Man