PK28908: TCP CONNECTION LOOPS WHEN INACTIVE >24 DAYS AND USING TIMESTAMPS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• TCPIP address space loops in SRB mode.  A TCP connection that
  has been inactive for more than 24 days and is using timestamps
  has become active and the timestamps being exchanged are
  invalid.
  
  SYSTRACE shows same pattern over and over:
  
  00 005E 09A2D988   SRB       070C0000 98CF32B8  00000000
  097E0454
  1A5EFD78
                                                  00000000 00
  00 005E 09A2D988   PC    ...   0      18E01B6A
  00331
  00 005E 09A2D988   PR    ...   0      18E01B6A 012EC952
  00 005E 0976A5E0   SRB       070C0000 98CF32B8  00000000
  097E0454
  1A39C120
                                                  00000000 00
  00 005E 0976A5E0   PC    ...   0      18E01B6A
  00331
  00 005E 0976A5E0   PR    ...   0      18E01B6A 012EC952
  
  Dump analysis of the SRB work will show it is inbound packet
  processing.  There will be a high number of packets dropped with
  reason of OLD TIMESTAMP so issuing a TCPIPCS TCB command on a
  dump will show a very high value in the 17th entry (Drop reason
  16) in the TCP_DROPIT array under the Main TCB Control Block
  (MTCB) information.
  .
  In the connection report, you may see the connection in a
  state of Closing.
  .
  KEYWORDS: dropit16 cpu looping loops shutdown hang hangs
            hanging abend071 s071 abends071
  
  ADDITIONAL SYMPTOMS:
  Telnet Obeyfiles failing with messages
  EZZ0677I THE CLIENT CONFIG SOCKET 3 TIMED OUT
  
  EZZ6035I TELNET DEBUG COMPONENT COMMAND CONTROL 629
    CONN: 00000000  LU: TELNET    MOD: EZBTMCTL
    RCODE: 0008-00  Storage obtain request failed.
    PARM1: 00000000 PARM2: 00000000 PARM3: 00000000
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communication Server    *
  *                 for z/OS Version 1 Release 4, 5, 6, 7 & 8    *
  *                 IP                                           *
  ****************************************************************
  * PROBLEM DESCRIPTION: TCP connections using the TCP Timestamp *
  *                      Option that are idle for more than      *
  *                      24 days may hang.                       *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  A TCP connection is established and the TCP Timestamp option
  is used. Packets flow normally, then the connection goes idle
  for more than 24 days, but remains established. Finally, a
  packet arrives and is accepted. However, every packet afterwards
  may fail the timestamp validation. As a result the connection
  hangs.
  
  The problem occurs because TCPIP incorrectly updates the last
  activity time in the TCB.
  +-------------------------------------------------------------+
  + 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

• The TCP send routine has been amended to update the last
  activity time field in the TCB before filling in the outbound
  timestamp.
  
  * 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:

  UK17594 UK17595 UK17596 UK17597 UK17598

Modules/Macros

• AFSNDINT EZBAFINB EZBAFWLM EZBTCFWR EZBTCSND
  EZBTCWRT EZBTLFWR TCSNDINT
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R140 PSY UK17594

     UP06/09/20 P F609

• R150 PSY UK17595

     UP06/09/20 P F609

• R160 PSY UK17596

     UP06/09/20 P F609

• R170 PSY UK17597

     UP06/09/20 P F609

• R180 PSY UK17598

     UP06/09/20 P F609

Fix is available

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