Understanding IPv6 and CICS

IPv6 is the protocol that replaces IPv4. To use IPv6 addressing, the sending and receiving environments must support dual-mode addressing (IPv4 and IPv6) and your CICS® regions must be running at the correct level of CICS.

Infrastructure requirements for IPv6

A dual-mode TCP/IP implementation is required to allow both IPv4 and IPv6 addressing. A single-mode (IPv4) environment uses the AF_INET address family when it establishes a connection between an AF_INET socket and another AF_INET socket in another region. IPv6 addresses are not supported over AF_INET sockets; these addresses require the AF_INET6 address family and AF_INET6 sockets in the sending and receiving regions to establish a connection. Dual-mode environments provide both AF_INET and AF_INET6 sockets. For more information on AF_INET and AF_INET6, see z/OS Communications Server: IPv6 Network and Application Design Guide.

This figure shows that a single-mode environment does not have IPv6 capability, because it does not have an AF_INET6 socket.
A single-mode environment and a dual-mode environment are shown. The single-mode environment has an AF_INET socket and IPv4 capability but it does not have IPv6 capability, because it does not have an AF_INET6 socket. The dual-mode environment has both AF_INET and AF_INET6 sockets, therefore it has both IPv4 and IPv6 capability.

CICS requirements for IPv6

You need a minimum level of CICS TS 4.1 to communicate using IPv6. The CICS region must be running in a dual-mode (IPv4 and IPv6) environment and the client or server with which CICS is communicating must also be running in a dual-mode environment.

The next figure shows CICS-to-CICS communication, where two dual-mode CICS environments can communicate using either IPv4 or IPv6 addressing. A single-mode CICS environment is also connected, but can communicate using IPv4 only.
The figure shows two dual-mode CICS TS 4.1 environments which can communicate using IPv4 and IPv6. A single-mode CICS TS 4.1 environment is also connected, but with IPv4 only.
The next figure shows CICS-to-CICS communication, where two dual-mode CICS environments can communicate using either IPv4 or IPv6 addressing. A dual-mode pre-CICS TS environment is also connected, but can communicate using IPv4 only.
The figure shows two dual-mode CICS TS 4.1 environments which can communicate using IPv4 and IPv6. A dual-mode pre-CICS TS 4.1 environment is also connected, but with IPv4 only.