IPv4-only stack

An IPv4-only stack supports AF_INET applications, but it does not support AF_INET6 applications. Start an IPv4-only stack in an integrated sockets environment in one of the following ways:

Do not code an AF_INET6 statement in BPXPRMxx. This method is the easier of the two. When AF_INET6 is not enabled, the underlying TCP/IP stack is started as an IPv4-only stack, even if it is capable of supporting IPv6.
Restriction: This is the only way to start z/OS® Communications Server TCP/IP as an IPv4-only stack in an integrated sockets environment.
Run a TCP/IP stack that is not capable of supporting IPv6. When starting a TCP/IP stack that does not support IPv6, the stack ignores any AF_INET6 definitions that might appear in BPXPRMxx. As a result, the stack is started as an IPv4-only stack, even when AF_INET6 is coded in BPXPRMxx.

When a TCP/IP stack is started as an IPv4-only stack in an Integrated Sockets environment, applications can open AF_INET sockets and can send and receive IPv4 packets over IPv4 interfaces only. However, applications are unable to open AF_INET6 sockets.