TCP packets ignored on ESTABLISHED connection

Issue

• TCP SYN packets ignored on ESTABLISHED connection
• When an external system is rebooted and tries to re-establish a TCP connection by re-using an existing port or tuple, the SYN packets are silently discarded. As per RFC 5961 section 4.2, RHEL should respond with a Challenge ACK.
• TCP SYN handling changed in RHEL 6.6
• The handling for receiving a SYN on an established socket. SYN is now discarded vs previously ACK (with current seq # of the old TCP conn from the client) would have been sent, which triggers RST from client as the sequence number is not expected.
• The backport of upstream kernel commit c3ae62af8e755 (tcp: should drop incoming frames without ACK flag set) to the RHEL 6.6 kernel breaks RFC5961-compliant behavior for SYN packets, potentially causing problems with CLOSE_WAIT sockets.
• tcp: Restore RFC5961-compliant behavior for SYN packets
• The tcp connection is not closed properly and remains in LAST_ACK state
• Solaris NFS Client cannot mount from RHEL NFS server after the client is powered off unexpectedly. Restarting the NFS Server allows the client to mount again.