Modifying HiperSockets connectivity [TCP/IP device and link and the VTAM HiperSockets MPC group (IUTIQDIO)]

Certain modifications can be made to the HiperSockets™ device (MPC group) without disrupting an active TCP/IP stack.

z/OS® supports dynamic I/O for the HiperSockets CHPID and subchannel devices, allowing subchannel devices to be added or removed to or from an LPAR which has already been IPLed.

TCP/IP supports the STOP and START command for the DYNAMICXCF HiperSockets device (IUTIQDIO). However, the commands are supported only when the (internal) start (activation) was successful during stack initialization. TCP/IP also supports the STOP and START command for the user-defined HiperSockets devices (IUTIQDxx). Because a user-defined HiperSockets device is supported as an MPCIPA device, STOP and START function just as they would for other MPCIPA devices.

VTAM® supports a MODIFY VTAMOPTS command that you can use to change the initial setting of the IQDCHPID start option.

Therefore, it is possible to make certain changes to the DYNAMICXCF HiperSockets MPC group (IUTIQDIO) without restarting VTAM or an active TCP/IP stack. Examples of changes that can be made are (STOP/START device required):

Alter which specific IQD CHPID is used for DYNAMICXCF (for example, move from the x'FC' CHPID to the x'FD' CHPID).
Add or remove subchannel devices (for example, from the current IQD CHPID).
Alter the IQD MFS which alters the TCP/IP MTU (for example, increase the current IQD CHPID from 16k to 64k).

Although VTAM supports modifications to the start option IQDCHPID (and the modification will be immediately displayed), the effects will vary depending on what the current usage was and the change (from or to) that was made. For example:

When MODIFIED from ANY (or CHPID) to NONE, there is no effect on current usage but blocks subsequent activations of the DYNAMICXCF HiperSockets device.
When MODIFIED from NONE to ANY (or CHPID), there is no effect on current usage but allows subsequent activations.
When MODIFIED from CHPID_X to CHPID_Y, there is no effect on current usage.
Note: VTAM uses the CHPID value only when building the IUTIQDIO MPC group.
To change CHPIDs for an active MPC group, take the following steps:
1. TCP/IP IUTIQDIO devices and IQDIOINTF6 interfaces that are changing must be stopped.
2. Make any necessary HCD/IOCDS changes.
3. Verify new subchannel devices are varied online.
4. Verify the MPC group has deactivated (with no usage it times out after approximately 2 minutes).
5. Modify IQDCHPID = CHPID (to new CHPID).
6. Restart the TCP/IP IUTIQDIO devices and IQDIOINTF6 interfaces.

To use HiperSockets communications, the processor must have the necessary hardware support. If the processor does not support HiperSockets communications, modifications to this start option will not be accepted, and the IQDCHPID option will not be displayed (displayed as ***NA***).