Defining TCP/IP as a UNIX System Services physical file system

The TCP/IP services stack in z/OS® Communications Server must be defined as a z/OS Communications Server UNIX System Services physical file system (PFS) before it can be started. This involves updating the BPXPRMxx parmlib member. The following sample definition in BPXPRMxx defines TCP/IP as a z/OS Communications Server UNIX System Services PFS, where the network layer is IP Version 4 (IPv4) and communication at the sockets layer is through the AF_INET family:

FILESYSTYPE TYPE(INET)  ENTRYPOINT(EZBPFINI)
 
NETWORK DOMAINNAME(AF_INET)
        DOMAINNUMBER(2)
        MAXSOCKETS(60000)
        TYPE(INET)

This sample definition shows how to define a single TCP/IP stack as IPv4 only. To define a single TCPIP stack as both IPv4 and IPv6, add an additional NETWORK statement in the BPXPRMxx member. The following sample definition in BPXPRMxx defines TCP/IP as a z/OS Communications Server UNIX System Services PFS, where the network layer is IP Version 6 (IPv6) and communication at the sockets layer is through the AF_INET6 family:

NETWORK DOMAINNAME(AF_INET6)
        DOMAINNUMBER(19)
        MAXSOCKETS(60000)
        TYPE(INET)

The BPXPRMxx member contains additional parameters that are crucial to the correct operation of TCP/IP. Carefully examine and specify these parameters:

MAXPROCSYS — Specifies the maximum number of z/OS UNIX processes that the system allows.
MAXPROCUSER — Specifies the maximum number of processes that a single z/OS UNIX user ID can have concurrently active, regardless of how the processes were created.
Guideline: The TN3270E server creates five UNIX processes at initialization and one more process for each BEGINVTAM statement that is used to define a listening port. For example, if 25 ports are defined by BEGINVTAM statements, then the TN3270 server creates at least 30 UNIX processes. If the TN3270E Telnet server is not running as UID(0) and has 20 or more ports defined (BEGINVTAM statements), increase the number of UNIX processes. You can increase the number of UNIX processes by increasing the value for MAXPROCUSER in the BPXPRMxx parmlib member, or by setting the PROCUSERMAX value in the OMVS segment for the TN3270E user ID.
MAXUIDS — Specifies the maximum number of z/OS UNIX user IDs that can operate concurrently.
MAXFILEPROC — Specifies the maximum number of descriptors for files, sockets, directories, and any other file system objects that a single z/OS UNIX process can have concurrently allocated. This includes access to both z/OS UNIX files and socket descriptors. In z/OS Communications Server, most TCP/IP applications access TCP/IP sockets, either directly or indirectly, using the TCP/IP socket APIs. You should set the MAXFILEPROC value high enough to accommodate the largest number of sockets that a single TCP/IP application (or z/OS UNIX process) can allocate.
Result: The TN3270E Telnet server running as UID(0) or running with BPX.SUPERUSER authority programmatically raises this limit beyond the MAXFILEPROC value, up to the system-defined maximum.

Guideline: If the TN3270E Telnet server or another application cannot programmatically raise this limit because the application is not running as UID(0) or with BPX.SUPERUSER authority, you can override the MAXFILEPROC limit by using the FILEPROCMAX parameter on the RACF® ALTUSER command (or using the appropriate command for your security product).
MAXPTYS — Specifies the maximum number of pseudo-terminals for the system.
MAXTHREADTASKS — Specifies the maximum number of MVS™ tasks that a single process can have concurrently active.
MAXTHREADS — Specifies the maximum number of threads that a single process can have concurrently active.
MAXQUEUEDSIGS — The sum of MAXQUEUEDSIGS and MAXFILEPROC multiplied by 2 is the system-wide maximum for the total number of asynchronous z/OS UNIX socket calls that can be outstanding. When you are specifying this number, consider:
- For every TCP/IP connection that the TN3270E Telnet server has, there is an asynchronous z/OS UNIX socket call outstanding, which is true for both TN3270 and TN3270E clients.
- Any TCP/IP application, from IBM® or supplied by a vendor, that uses either the z/OS UNIX asyncio callable service or the TCP/IP-provided Sockets Extended asynchronous API can have one or more outstanding asynchronous socket calls.

The MAXSOCKETS parameter specifies the maximum number of sockets that can be obtained for a particular file system type. You must ensure that this specification is large enough to accommodate your installation workload. For example, each connection to your TN3270E Telnet server or FTP server requires one z/OS UNIX System Services socket. When the maximum number of sockets is allocated, then no more Telnet sessions, FTP sessions, or other applications that require z/OS UNIX System Services sockets can be started.

Note: If multiple NETWORK statements are defined, MAXSOCKETS can be specified for each NETWORK statement and will be enforced separately.

For details on the BPXPRMxx member, see: