OA41007: DURING PSRETRY PROCESSING THE OPTIMAL PATH IS NOT CHOSEN

APAR status

• Closed as program error.

Error description

• During a network outage an RTP PU is path switched to a back up
  route that has a higher weight then the original path. When the
  original path becomes available PSRETRY should switch the route
  back to the lower weight path. However the route remains on the
  higher weight path.
  

Local fix

• Issue a Modify RTP ID=CNRxxxxx to force the path switch.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of VTAM/RTP connections.           *
  ****************************************************************
  * PROBLEM DESCRIPTION: PSRETRY does not pick the best path.    *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The problem may be summarized as follows:
  1. There is an RTP connection between zOS CS and a non-z/OS
     CS HPR node. PSRETRY is coded for VTAM.
  2. The non-VTAM HPR node sends in a Route Information segment
     as part of a path switch process, but THD_RIN_WEIGHT
     had a value of 0 set, indicating a path weight of 0.
  3. At the next PSRETRY interval, VTAM's RTP code sees the
     path weight of 0 and assumes that this is a special case
     where it needs to learn the weight of the route without
     path switching.  This leads to VTAM associating an
     incorrect weight with the HPR pipe.
  4. Later, when a better path is available, VTAM does not
     path switch to use that route because the weight that it
     mistakenly associated with the route selected by the
     non-VTAM HPR node makes that path appear to be just as good
     or better.
  

Problem conclusion

• ISTRPCRI has been updated to set RPN_PATH_WEIGHT to x'FFFF'
  if the Route Information Segment arrives with a weight of
  0 and RPN_PATH_WEIGHT is non-zero. After this occurs, at
  the next PSRETRY interval, VTAM should force a path switch
  to the optimal weight and set the correct weight.
  
  ISTRPNCB defined a new constant for x'FFFF'.
  
  ISTRPCRT is included for maintenance purposes only.
  

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:

  UA67546 OA41151

Modules/Macros

• ISTRPCRI ISTRPCRT ISTRPNCB
  

Fix information

• Fixed component name

  VTAM V4 MVS/ESA

• Fixed component ID

  569511701

Applicable component levels

• R1B0 PSY

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