HiperSockets connectivity and routing

For each pair of stacks within a sysplex that are not on the same MVS™ image, if all of the following conditions are true, the stacks will use HiperSockets™ DYNAMICXCF connectivity (versus standard XCF connectivity):

The two stacks must be on the same CPC.
For the DYNAMICXCF HiperSockets device (IUTIQDIO):
- The two stacks must be using the same IQD CHPID.
- If running on a system that supports multiple channel subsystems and the two stacks are also in different channel subsystems, the IQD CHPID must be configured (HCD) to span.
Both stacks must be configured (HCD) to use HiperSockets.
For IPv4 HiperSockets connectivity, both stacks must be at the z/OS® V1R2 level, or a later release. For IPv6 HiperSockets connectivity, both stacks must be at the z/OS V1R7 level.
The initial HiperSockets activation must complete successfully.

When an IPv4 DYNAMICXCF HiperSockets device and link are created and successfully activated, a subnet route is created across the HiperSockets link. The subnet is created by using the DYNAMICXCF IP address and mask. This allows any LPAR within the same CPC to be reached, even ones that are not within the sysplex. For example, an LPAR that is running z/Linux or z/VM® that does not support joining the sysplex can still be reached. The z/Linux or z/VM LPAR must define at least one IP address for the HiperSockets endpoint that is within the subnet defined by the DYNAMICXCF IP address and mask.

Similarly, when an IPv6 DYNAMICXCF HiperSockets interface is created and successfully activated, a prefix route is created across the HiperSockets interface (if prefix_route_len is specified on DYNAMICXCF). This allows any LPAR within the same CPC to be reached, even ones that are not within the sysplex. For example, an LPAR that is running z/Linux or z/VM that does not support joining the sysplex can still be reached. The z/Linux or z/VM LPAR must define at least one IP address for the HiperSockets endpoint that uses the same prefix as the DYNAMICXCF IP address.

Therefore, TCP/IP can communicate with other LPARs within the CPC over the HiperSockets connectivity created by DYNAMICXCF even when the TCP/IP in the other LPAR is not part (joins or supports) of the sysplex. You can also elect to manually configure a HiperSockets device for non-sysplex communications.

When multiple stacks are within the same LPAR that supports HiperSockets, both IUTSAMEH and HiperSockets links or interfaces will coexist. In this case, it is possible to transfer data across either link or interface. Because IUTSAMEH links or interfaces have better performance, it is better to always use them for intra-stack communication. A host route will be created by DYNAMICXCF processing across the IUTSAMEH link or interface but not across the HiperSockets link or interface. To avoid using the HiperSockets link or interface for communication within the same host, the following rules should be observed:

Specify DYNAMICXCF IP addresses in a separate subnet than that of VIPA addresses (IPv4) or using a separate prefix than that of VIPA addresses (IPv6).
Do not specify static IUTSAMEH links or interfaces.

It is also possible with multiple stacks in the same LPAR to end up with both XCF and HiperSockets links or interfaces. This occurs when the availability of the (preferable) HiperSockets link or interface changes as each TCP stack (within the same LPAR) is started. For example, stack A is started with HiperSockets available and later stack B is started with HiperSockets unavailable. This type of configuration should be avoided.