Large number of "invalid SYN cookies" on RHEL 7 running httpd

Solution Verified - Updated -

Issue

  • netstat shows a large number of "invalid SYN cookies"
  • httpd terminates sessions earlier than expected, causing clients to reconnect and increasing latency.
  • When comparing http traffic between RHEL 6 and RHEL 7, this issue may appear as a lower than expected number of connections and httpd workers on RHEL 7.

Environment

  • Red Hat Enterprise Linux 7
    • httpd 2.4.6
    • httpd 2.4.37

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