Message-flooding prevention

Certain messages in VTAM® can be issued several times for an event without supplying new information to the operator (for example, IST264I is issued for each attempted logon from multiple terminals to an undefined application program). These repeating messages can overwhelm an operator console or program operator application, and critical messages could be concealed in this volume of information. To alleviate this occurrence, VTAM includes a message-flooding prevention mechanism.

VTAM uses a table containing a list of pre-designated messages that are candidates for flooding suppression. There is default IBM-supplied table, ISTMSFLD, or a user-defined message-flooding table can be defined. For more information on message-flooding prevention, defining your own message-flooding prevention table, and the IBM-supplied message-flooding prevention table, see the z/OS Communications Server: SNA Resource Definition Reference.

The message-flooding prevention table specifies, for each message, the criteria that must be met to prevent the message from being reissued. A message is a candidate for suppression if it is listed in the table and meets the following criteria:

  1. Time-span: The message is issued a second time in the specified amount of time (the default is 30 seconds).
  2. Suppressible variable-text fields: The specific variable fields listed in the table contain the same information for this issuance of the message as the previous issuance. Only fields listed in the table are checked. The message may have other variable fields which can have different values and still result in suppressing the message.

If the above criteria are met, the message is suppressed. When a message is suppressed it will not be routed to the program operator application or system console to which it was destined. However, the message may be sent to the system hardcopy log if it was destined for the system console, based on the HARDCOPY specification in the message-flooding prevention table (the default in ISTMSFLD is that the message be sent to the system hardcopy log).

Note: The message-flooding prevention table prevents specific messages from being issued by VTAM. This may affect network management application command lists and any automated operations facilities at your installation.