Client application with fixed source port cause tcp out of state easily

[AK2020]

For a client application using fixed source ports, when the client cannot connect a server suddenly and then re-establish a SYN packet, checkpoint firewalls may block the packet if it contains a session with a tcp state like pre-closing or post-closing. If the corresponding firewall rule disabled the TCP sequence check, will checkpoint allow the SYN packet and then let the 3-way handshake to complete and then reuse (or overwrite) the session so that the state changes from pre-closing to established?

[PhoneBoy]

This is not a sequence verifier issue, it's likely a feature called Smart Connection Reuse.
You can modify the behavior here:
https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solut...

[AK2020]

Thank you very much for your reply. I had read the link you gave me before and found that Smart Connection Reuse works well for established connection maintained in session tables. For half closed connections, it had had a bug before and had already patched:

https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solut...,

In my environment, when my application re-established a connection, the firewall blocked the SYN packet because it found it is TCP out of sync. Because of this, I believed it was related to TCP sequence verification. So, I am thinking if disable then TCP sequence verification can be a workaround too.