PM76343: TELNET LOOPS WHEN USING 3270 CONNECTIONS AND GENERIC TAKEOVER

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• TN3270 is configured with TKOGENLU.  A Telnet connection which
  is not using TN3270E connects and attempts a takeover.  Telnet
  incorrectly issues multiple receives requests on the socket.  If
  the remote client sends in large amounts of data, the receives
  will run in EZBTTRCV at the same time.  This can cause Telnet to
  loop in EZBTPTDP trying to process a SKMB chain that points to
  back on itself.
  

Local fix

• Disable generic takeover by coding NOTKOGENLU in TELNETGLOBALS.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Releases 12 and 13 IP:    *
  *                 Telnet Services                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Loop in EZBTPTDP due to a message       *
  *                      triple pointing back to itself.         *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The problem may be summarized as follows:
  1. TKOGENLU or TKOSPECLU is coded in the profile.
  2. A TN3270 mode client connects to the Telnet server.
  3. A second client with the same IP address connects
     to the Telnet server, driving the takeover process.
  4. During the takeover process, two asynchronous receives
     are issued using the same control block.
  5. The receive exit runs simultaneously for the two receives
     corrupting the message triple chain.
  6. A later reference to the message triple chain results in
     a loop.
  +-------------------------------------------------------------+
  + 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

• EZBTTCSC is updated to prevent two receives from being
  issued during the takeover process for TN3270 mode
  clients.
  
  * Cross Reference between External and Internal Names
  

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:

  UK83651 UK83652

Modules/Macros

•    EZBTTCSC
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1C0 PSY UK83651

     UP13/01/11 P F301

• R1D0 PSY UK83652

     UP13/01/11 P F301

Fix is available

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