PM76397: DISTRIBUTED PASSIVE CONNECTIONS FAIL CONNECTION ESTABLISHMENT

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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 number

    PM76397

  • Reported component name

    TCP/IP V3 MVS

  • Reported component ID

    5655HAL00

  • Reported release

    1D0

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-11-02

  • Closed date

    2012-12-03

  • Last modified date

    2013-02-04

  • 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

  • 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 #:

PM76397

Modified date:

2013-02-04

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