PM76343: TELNET LOOPS WHEN USING 3270 CONNECTIONS AND GENERIC TAKEOVER

A fix is available

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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.
    .
    ADDITIONAL SYMPTOMS:
    ABEND4C5 RC74FF2000 rc2000 2000 EZBITDSA TcpitProcStackExceeded
    ABEND0C4 EZBTPTDP
    

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 number

    PM76343

  • Reported component name

    TCP/IP V3 MVS

  • Reported component ID

    5655HAL00

  • Reported release

    1D0

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-11-01

  • Closed date

    2012-11-19

  • Last modified date

    2013-09-13

  • 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

  • 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.



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Document information


More support for:

z/OS family

Software version:

1D0

Operating system(s):

z/OS

Reference #:

PM76343

Modified date:

2013-09-13

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