PQ61947: CSM 4K ECSA STORAGE GROWTH WHEN USING CLAW PACKING AND MULTIPATH

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When running CLAW Packing and MULTIPATH it is possible for the
  wrong MTU size to be used when building an outbound packet.
  If the size of a packet is close to 4K it can cause a large
  amount of CSM 4K ECSA allocations to be obtained when trying to
  pack the datagram into a packing buffer. The buffers will
  primarily contain data with eyecatchers of IUDR.
  VERIFICATION STEPS:
  1) use VERBX VTAMMAP 'CSMOWNER CSMOWNID(xx)' for TCPIP asid
     and look for a large number of 4K ECSA buffers in use by
     TCPIP
  2) The buffers will contain an IUDR with a PIF (offset x'20')
     that is for a Claw device, offset x'4' will have the
     dlruppdu bit on (x'02') that indicates packed pdu but the
     the PDU descriptor area (offset x'80') will contain zeros
     for the first 12 bytes and the number of PDUs at offset x'8'
     in the IUDR will be zero.
  3) The customer is running with MULTIPATH on.
  

Local fix

• Turn off MULTIPATH
  .
  KEYWORDS: PACKED CLAW PACKING ECSA CSM IUDR MULTIPATH STORAGE
            GROWTH
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the Communications Server for   *
  *                 OS/390 Release 8 & 10 IP and                 *
  *                 z/OS Release 2 IP:  MULTIPATH routing        *
  ****************************************************************
  * PROBLEM DESCRIPTION: A loop in EZBIFOUT may occur when using *
  *                      CLAW packing.  The loop allocates CSM   *
  *                      4K ECSA storage and will not release    *
  *                      it, causing a storage shortage.         *
  *                      The incorrect MTU may be used when      *
  *                      multipath routing is enabled for TCP    *
  *                      based connections.                      *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  When MULTIPATH routing is enabled, an MTU is maintained for each
  set of multipath routes.  The multipath groups MTU is set to the
  smallest MTU of any route in the group.  Each routes MTU is set
  based on the MTU supported by the device, or the MTU specified
  in the BEGINROUTES or GATEWAY statement.  When CLAW packing is
  enabled, the devices MTU is adjusted to provide space for the
  packing control data.  The adjusted MTU is being set correctly
  in the routes over the device in the routes adjusted MTU field.
  The multipath groups MTU is being set based on the routes MTU
  instead of the adjusted MTU, resulting in a multipath MTU that
  exceeds the usable MTU for a CLAW packing device.
  The packing code in EZBIFOUT determines there is not enough room
  for the packet and packing control in a packing buffer.  A new
  CSM 4K ECSA packing buffer is allocated.  The packet will never
  fit into a packing buffer so the code loops.
  +-------------------------------------------------------------+
  + 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

• EZBIPRTE has been amended to set the MTU for multipath routes
  to the smallest adjusted MTU in the group.
  
  * Cross Reference between External and Internal Names
  

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:

  UQ67763 UQ67764 UQ67765

Modules/Macros

• EZBIPRTE
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R120 PSY UQ67763

     UP02/08/02 P F208

• R380 PSY UQ67764

     UP02/08/02 P F208

• R50A PSY UQ67765

     UP02/08/02 P F208

Fix is available

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