PM87042: S4C5/77BD0402 ABEND IN EZBXFMS6 ON A SYSPLEX DISTRIBUTOR

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A system is configured as a Sysplex Distributor for a DVIPA with
  SYSPLEXPORTS enabled.  The potential exists for SYN packet to
  arrive at the distributing system before the NEWCONN message
  from the target system identifying the listener has been
  processed.  Normally this would result in the distributor
  holding on to the SYN packet until after the NEWCONN arrives,
  and at that time forwarding it to the target to complete the
  connection.  However if the LIF cache entry on the device over
  which the packet originally arrived is replaced during this
  period, there are two symptoms:
  
   - A RESET for that connection will be sent back to the
     originating client, causing a connection failure.  The exact
     symptoms for this on that client will depend on the
     application being used.
  
   - If another SYN packet arrives with the same 4-tuple (client
     IP address and port, and server IP address and port) during
     the next six minutes, the processing for that packet will
     trigger an ABEND trying to process the old connection
     information (XFCRHTE).
  
  
  Possible ABEND symptoms seen:
  
   - UNKNOWN (??????? ??????)+?????? S4C5/77BD0402
   - EZBITSTO(HIP61D0 11.090)+0027C2 S4C5/74BE2506
  
  
  Other symptoms:
  
   - The ABENDing DUCB will have gone through the Remove_CRHT
     routine in EZBXFMS6.
  

Local fix

• This problem is most likely to occur FTP server sessions using
  passive transfers and having PASSIVEDATAPORTS specified.
  Increasing the size of this range will reduce the likelihood of
  the same port numbers being used with the same client system
  during that six minute period.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communication Server    *
  *                 for z/OS Version 1 Release 13                *
  *                 IP: Distributed DVIPA                        *
  ****************************************************************
  * PROBLEM DESCRIPTION: Connections using sysplexports reset    *
  *                      and XFCRHTE hash table points to        *
  *                      freed storage resulting in ABEND4C5     *
  *                      RC 77BD0402                             *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  A scenario exists which can cause connections to a distributed
  DVIPA using sysplexports to be reset and potentially cause
  an abend.  The problem is summarized as follows:
  1. An application on a target stack binds and listens to
     DVIPA A port B.  An XCF message is sent to the distributor.
  2. Prior to the XCF message arriving, a SYN is received for
     DVIPA A port B.  A XFCRHTE is created with the SYN queued
     to it.
  3. The XCF message arrives from the target.  EZBIPINB is
     scheduled to send the queued SYN to the target
  4. EZBIPINB incorrectly sets the logical interface the SYN
     was received on if the DVIPA address is no longer in the
     physical interface cache.
  5. The SYN is sent to the TCP layer on the distributor,
     causing a reset to be sent to the remote client.
  6. If DVIPA A Port B is reused by another application, an
     entry will be added to the XFCRHTE hash table which points
     to freed storage.  This can cause abends when the connection
     is closed by the application.
  +-------------------------------------------------------------+
  + 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

• TCPIP has been modified to correctly forward the SYN to the
  target stack.
  
  * 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:

  UK94181 PM88785

Modules/Macros

• EZBIPINB EZBXFACI EZBXFHSH EZB2IUDR TPSTMSG1
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1D0 PSY UK94181

     UP13/06/11 P F306

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.