OA43910: EZBITDSA ABEND 4C5 74FF2500 ABEND0C4 EZBUDBYP SP241 TCP ECSA DUCB DUSA SHORTAGE PORT 12001 UCB LOCK

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Outbound traffic backed up on port 12001 waiting on the UCB
  lock.  The lock contention is causing DUCB expansion and
  suspended SRBs that quickly exhaust ECSA.  The current
  design that requires serializing EE outbound requests on a
  given port is unable to sustain high volume traffic.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Releases 12 and 13 SNA:   *
  *                 Enterprise Extender                          *
  ****************************************************************
  * PROBLEM DESCRIPTION: Abend ABEND4C5 reason code 74FF2500     *
  *                      when contention exists on the UCB lock  *
  *                      for Enterprise Extender port 12001      *
  *                      traffic.                                *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The problem is summarized as follows:
  1) EE configuration consisted of multiple local VIPAs active
     with connections to over 10,000 EE partners.
  2) Remote EE partners were being rebooted in large numbers.
     The remote partners are end nodes (EN) which require
     CP-CP and DLUS support.
  3) The large scale network activity generated 1000s of
     data packets for port 12001.
  4) Each of these packets must pass through the TCP/IP
     FastUDP layer, which acquires the UCB lock exclusively to
     update route as well as policy information.
  5) In this configuration, a spike in network activity resulted
     in UCB port 12001 lock contention which caused TCP/IP
     DUCBs to become suspended.  This leads to a slowdown of
     outbound EE traffic and a growth in ECSA.  In this case,
     ECSA growth expands until it is exhausted leading to the
     reported abends.
  Note: In the dump provided, there were over 9000 DUCBs
     suspended on the UCB lock.
  
  The PTF for TCPIP APAR PI06478 must be installed before or
  concurrently with the PTF for this APAR.
  

Problem conclusion

• Enterprise Extender processing for outbound traffic
  has been optimized to better handle large amounts of outbound
  traffic.  The basic design is for VTAM to pass a queueing
  structure, IUTIPNEE, along with IUTIL PLISTs to the TCP/IP
  stack when crossing the IUTSAMEH connection.  These
  queueing structures, IUTIPNEEs, allow for concurrent processing
  while setting a maximum number of outbound threads of
  execution that can potentially suspend on a UCB lock
  
  This design allows for 16 queueing structures for each
  port priority, and 16 queueing structures to handle ANR
  routed HPR traffic, for a given local static EE VIPA.
  These queueing structures are assigned to each line
  during activation for the life of the line.  These new
  structures allow a serialization point for outbound traffic.
  If FastUDP is busy processing a previous signal for EE, a new
  request will simply queue up on this structure and exit
  processing.  This exit alleviates the need for the
  running DUCB as well as the SRB itself.  When the previous
  process finishes up the current request, it will simply
  continue to process the remaining elements until all
  outbound work is complete.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

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

  UA71699 UA71698 OA44090

Modules/Macros

• ISTAUCAL ISTAUCDL ISTAUCFT ISTAUCLA ISTAUNCB
  ISTIPNCB ISTRAFME ISTRAFM1 ISTRLN   ISTRPCDU ISTRPNCB ISTTSC89
  

Fix information

• Fixed component name

  VTAM V4 MVS/ESA

• Fixed component ID

  569511701

Applicable component levels

• R1C0 PSY UA71698

     UP14/02/21 P F402 Ž

• R1D0 PSY UA71699

     UP14/02/21 P F402 Ž

Fix is available

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