PM76397: DISTRIBUTED PASSIVE CONNECTIONS FAIL CONNECTION ESTABLISHMENT

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A timing window exists in the connection establishment on a
  distributed passive connection which can prevent establishment
  from completeing.  The sequence of events proceeds as follows:
  
  1. The NEWCONN message from the target and the SYN from the
  remote client arrive almost simultaneously.
  
  2. The DUCB for the client's SYN searches the CRHT for an entry
  for the passive connection, and finds none.
  
  3. The DUCB for the target's NEWCONN searches the CRHT for a
  SYNQ, and finds none.
  
  4. The DUCB for the target creates the CRHT entry with a
  2-tuple.
  
  5. The DUCB for the client creates a CRHT entry with a 4-tuple
  
  6. All subsequent SYNs to the target match to the 4-tuple as it
  is more specific, and are never forwarded on to the target.
  Eventually, the connection is aborted.
  
  
  Verification Steps:
  A SYSTCPIP trace taken on the distributor stack will show a
  sequence of entries similar to the following:
  
  Client's DUCB               Target's DUCB
  ---------------------       ---------------------
  ...                         IXCMSGI macro
  ...                         Entry
  ...                         Find ptb
  ...                         Trace input buffer
  Find Connection Entry       ...
  ...                         Main Path AddConn
  Main Path AddConn           ...
  Add Connection Entry        ...
                              Add Connection Entry
  

Local fix

• Retry the connection.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Release 13                *
  *                 IP: Distributed DVIPA                        *
  ****************************************************************
  * PROBLEM DESCRIPTION: Connections fail to establish to a      *
  *                      Distributed DVIPA.                      *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  During connection establishment to a Distributed DVIPA
  for a passive connection a target stack notifies the
  sysplex distributor to create a connection route entry.
  If a SYN arrives at the distributor before the target
  stacks notification, the SYN is queued until the
  notification arrives. There is a small timing window
  during which the target notification arrives at the same
  time as the SYN, but the connection route entry is not yet
  created. The SYN is queued and all subsequent SYNs are
  dropped until the connection is aborted.
  +-------------------------------------------------------------+
  + 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 search for the connection
  route entry created by the target when the SYN arrives.
  
  * 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:

  UK90670

Modules/Macros

• EZBXFUT3 EZBX6UT3
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1D0 PSY UK90670

     UP13/02/01 P F301

Fix is available

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