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RaphaelL's avatar
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Oct 15, 2021

TCP Closing session with wrong SEQ and ACK

Hi ,


While troubleshooting an issue with a connexion towards our LTM , I did a packet capture and I was intrigued by the way our LTM is closing it's TCP sessions.


The client sends a FIN,ACK , the LTM responds with a ACK then a FIN,ACK and finally the client sends a ACK and the session is closed and everyone is happy... except Wireshark !


The LTM seems not to be using the wrong SEQ and ACK numbers in its FIN,ACK and Wireshark flags both packets as TCP out of order ( since the numbers don't match up )


Here is an example :




We are running : BIG-IP Build 0.16.5 Engineering Hotfix


Anyone have an Idea why are we seeing this odd behavior ?


Thanks ,

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