PI11640: SNMP GET OF IFLASTCHANGE MIB CAUSES TCPIP DIVIDE OVERFLOW

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Hardware failure of one OSA card caused the z/VM TCP/IP stack
  to abend.  The error was actually caused by an SNMP GET request
  of the ifLastChange MIB variable that was issued by an SNMP
  management agent after z/VM TCP/IP sent an SNMP trap message
  to the agent to report the fact that the link had went down.
  While processing the SNMP GET request, TCP/IP must calculate
  how long the interface had been up prior to going down
  (ifLastChange equals the value of sysUpTime at the time the
  interface changed state).  During this calculation, the divide
  overflow error occurs because the interface had been up long
  enough (greater than 248 days) to cause the number of ticks
  (hundredths of a second) to not fit in an unsigned integer.
  The error occurs when the DoubleDivide routine is called by
  the TimeDiffToTimeTicks routine inside TCMIB PASCAL.  The
  following error messages are displayed on the TCP/IP console
  just prior to the TCP/IP system abending:
  .
   AMPX019I FIXED POINT DIVIDE BY ZERO EXCEPTION
         TRACE BACK OF CALLED ROUTINES
   ROUTINE                STMT AT ADDRESS IN MODULE
   TIMEDIFFTOTIMETICKS       3    00E60392   TCMIB
   GET_IFENTRY              64    00DF6FC2   TCMIB
   PROCESSMIBREQUEST        45    00DFB1E0   TCMIB
   DOAGENTREQUEST           15    00DF2EE6   TCSNMDPI_SNMP_DPI
   SNMPDPIPROCESS            7    00DF3170   TCSNMDPI_SNMP_DPI
   Schedule               2082    00CDA2E4
   <MAIN-PROGRAM>           14    00C181FE   TCPIP
   VSPASCAL                        00E4943A
  .
   AMPX015I ADDRESSING EXCEPTION
         TRACE BACK OF CALLED ROUTINES
   ROUTINE                STMT AT ADDRESS IN MODULE
   TIMEDIFFTOTIMETICKS       0    00CF1B24   TCMIB
   GET_IFENTRY              64    00DF6FC2   TCMIB
   PROCESSMIBREQUEST        45    00DFB1E0   TCMIB
   DOAGENTREQUEST           15    00DF2EE6   TCSNMDPI_SNMP_DPI
   SNMPDPIPROCESS            7    00DF3170   TCSNMDPI_SNMP_DPI
   Schedule               2082    00CDA2E4
   <MAIN-PROGRAM>           14    00C181FE   TCPIP
   VSPASCAL                       00E4943A
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the z/VM SNMP server            *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  ****************************************************************
  * RECOMMENDATION: APPLY PTF                                    *
  ****************************************************************
  The problem is that when the 'ifLastChange' or 'sysUpTime'
  MIB variable is requested, the SNMP server needs to return
  the answer in a signed integer variable.  When the value
  of the MIB variable is greater than around 248 days, it
  exceeds the maximum value that will fit in the variable.
  This causes a division error that leads to the TCP/IP
  stack abending.
  

Problem conclusion

• Code has been updated such that when the value of
  'ifLastChange' or 'sysUpTime' is greater than the
  variable can accommodate, the counter will wrap back
  to zero rather than causing an abend.
  ----------------------------------------------------
  The following documentations need to be updated.
  ----------------------------------------------------
  The description about SysUpTime and ifLastChange
  need to be updated in TCPIP User's Guide (SC24-6240-05)
  as follows:
  In TCPIP User's Guide:
  Appendix E. Management Information Base Objects
    -> System Group
    -> Table 40. Implementation of the System Group
    -> Object SysUpTime -> Definition
       update definition for SysUpTime in table 40
  The time (in hundredths of a second) since the network
  management portion of the system was last started.
  The maxmium value of the time is around 248 days. When
  the value of the time is greater than the maxmium value,
  the counter will wrap back to zero.
  +++++++++++++++++++++++++++++++++++++++++++++++++++++++
  Appendix E. Management Information Base Objects
    -> Interfaces Group
    -> Table 41. Implementation of the Interfaces Group
                 (continued)
    -> Object ifLastChange -> Definition
       update definition for ifLastChange in table 41
  The value of sysUpTime at the time the interface
  entered its current operational state. If the current
  state was entered before the last start-up of the local
  network management subsystem, then this object contains
  a value of 0. The maxmium value of the time is around
  248 days. When the value of the time is greater than
  the maxmium value, the counter will wrap back to zero.
  

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:

  UI15836 UI15837 UI15854

Modules/Macros

• MIB_SYST TCMIB
  

Fix information

• Fixed component name

  TCP/IP V2 FOR V

• Fixed component ID

  5735FAL00

Applicable component levels

• R540 PSY UI15854

     UP14/03/13 P 1401

• R620 PSY UI15836

     UP14/03/13 P 1401

• R630 PSY UI15837

     UP14/03/13 P 1501

Fix is available

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