TCP/IP Considerations

The Event/Automation Service is a z/OS® UNIX sockets application. Any z/OS sockets application needs to reference TCP/IP configuration data. The method of accessing this data is defined by the z/OS version of TCP/IP that is running. See the z/OS Communications Server IP Configuration Guide for general information about how z/OS UNIX sockets applications interact with TCP/IP. This information also discusses how a z/OS UNIX sockets application:

Gains affinity to a TCP/IP stack
Resolves names to IP addresses
Finds required TCP/IP configuration data sets

The z/OS Communications Server implements configuration search orders for determining stack affinity and resolver configuration. A commented SYSTCPD DD statement is provided in the sample Event/Automation Service start procedure to identify the location of the TCP/IP configuration data for these purposes. See the z/OS Communications Server IP Configuration Guide for information about how a z/OS UNIX sockets application uses the SYSTCPD DD statement, and determine if you must use a SYSTCPD statement in the Event/Automation Service startup procedure.

For stack affinity, particularly in a common INET(CINET) environment:

For all NetView-based z/OS UNIX sockets applications provided with Automation Control, the stack affinity is determined by UNIX System Services configuration definitions. See the z/OS Communications Server IP Configuration Guide for notes on multiple instances of TCP/IP.
In a z/OS UNIX INET (single stack) environment, the socket application program is always associated with the single TCP/IP stack. In the z/OS UNIX Common INET (CINET) environment, since the Event/Automation Service does not explicitly request affinity with a particular TCP/IP stack, the transport assigns affinity with one, which might not be the desired TCP/IP stack.
If you require the Event/Automation Service program to have affinity with a particular TCP/IP stack in a CINET environment, consider establishing affinity using the following method. The BPXTCAFF program can be used to obtain affinity with the TCP/IP stack of your choice. To do this, the BPXTCAFF program must run prior to the program that initializes the Event/Automation Service address space. One way of doing this is to add this statement in the Event/Automation Service start procedure just prior to the statement used to start Event/Automation Service program:
```
//STEP0 EXEC PGM=BPXTCAFF,PARM=MYSTACK
```
where the value of the PARM keyword is the name of the TCP/IP stack with which affinity is established. Using the sample Event/Automation Service start procedure, IHSAEVNT, as a starting point, this example illustrates what the steps of the Event/Automation Service start JCL might look like after the step is added. This example is for reference only.
```
//STEP0 EXEC PGM=BPXTCAFF,PARM=MYSTACK
//*
//STEP1 EXEC PGM=&PROG,TIME=1440,REGION=&REG,
// PARM=('/MSGCFG=&MSGCFG ALRTCFG=ALRTCFG ERCVCFG=&ERCVCFG*
// TALRTCFG=&TALRTCFG ALRTTCFG=ALRTTCFG PPI=&PPI *
// INITFILE=&INITFILE OUTSIZE=&OUTSIZE ROUTECDE=&ROUTECDE *
// &OELINE')
:
:
```