PQ73110: TCP LAYER SENDS PACKET WITH SYN FIN PSH BITS ALL SET

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Socket close processing sends an outbound TCP segment with SYN,
  FIN, PSH set on when the connection is in the SYNSENT state.
  This problem has been seen when an appliction using asynchronous
  sockets that closes a socket that does not complete a connect()
  request with a specific time.
  The presence of SYN, FIN, PSH in a single packet is not a
  protocol violation, however there are implementations
  that discard packets with this flag combination.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications          *
  *                 Server for OS/390 Releases 8 and 10, and     *
  *                 z/OS Version 1 Releases 2 and 4 IP.          *
  ****************************************************************
  * PROBLEM DESCRIPTION: A packet with the SYN, FIN and PSH      *
  *                      bits is sometimes sent to the target    *
  *                      host during close processing.           *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  During TCP connect processing retransmission the application
  issuing the connect detects a timeout and closes their socket.
  This causes a packet to be sent out to the target host with
  the SYN, FIN and PSH bits all on. This combination is not
  recognized as valid by some receiving hosts.
  +-------------------------------------------------------------+
  + Please check our Communications Server for OS/390 homepages +
  + for common networking tips and fixes.  The URL for these    +
  + homepages can be found in Informational APAR II11334.       +
  +-------------------------------------------------------------+
  

Problem conclusion

• The code has been changed to not send a FIN when there has
  been no acknowledgment of the initial SYN that was sent.
  
  * Cross Reference between External and Internal Names
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UQ77146 UQ77147 UQ77148 UQ77149

Modules/Macros

• EZBTCREQ
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R120 PSY UQ77146

     UP03/06/25 P F306

• R140 PSY UQ77147

     UP03/06/25 P F306

• R380 PSY UQ77148

     UP03/06/25 P F306

• R50A PSY UQ77149

     UP03/06/25 P F306

Fix is available

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