Mar 27, 2026 - For details about updated CVE-2025-53521 (BIG-IP APM vulnerability), refer to K000156741.

Forum Discussion

cwkim_261931's avatar
cwkim_261931
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Oct 18, 2018

The client sends a push-ack instead of ack to the response packet to syn-ack.

Hi   I have strange issue.   I know 3way-handshake is SYN->SYN-ACK->ACK.   But Someone is SYN->SYN-ACK->PUSH-ACK.....   What happen it is?   Is it normal?!   I guess, BIG-IP dorp it...
application delivery
big-ip
LTM
F5_Learner_3295's avatar
F5_Learner_3295
Icon for Nimbostratus rankNimbostratus
Oct 19, 2018

Hi ,

 

Can you paste the logs which shows sequence process.

 

This is basic TCP communications flow. The ACK indicates that a host is acknowledging having received some data, and the PSH,ACK indicates the host is acknowledging receipt of some previous data and also transmitting some more data.

Regards