While making HTTP call to server using Jmeter we see SYN flood. This is causing most probably since Jmeter doesn't sends back the ack as part of 3 way handshake.
Is there any way we can force Jmeter to send the ack back to Server for TCP Connection ?
Given connection succeeded JMeter should normally send ACK, there is no need to "force" it by any means (at least this is true for JMeter 5.2 and HttpClient4 implementation):
I would recommend double-checking incoming and outgoing packets using a lower level sniffer tool like Wireshark
You can also get extra information regarding what's going on under the hood by adding the next line to log4j2.xml file (lives in "bin" folder of your JMeter installation) to enable debug logging for the HTTP protocol
<Logger name="org.apache.http" level="debug" />
JMeter restart will be required to pick up the change.
