Static VIPAs, dynamic VIPAs, distributed DVIPAs

z/OS® TCP/IP stack supports two types of VIPAs: static and dynamic. Dynamic VIPAs (DVIPAs) can be used to distribute connections in a sysplex. This is referred to as a distributed DVIPA.

All three VIPAs can coexist on a given stack, but there are differences in how these VIPAs are configured and used.

Static VIPAs have the following characteristics:

They can be activated during TCP/IP initialization or VARY TCPIP,,OBEYFILE command processing, and are configured using an appropriate set of DEVICE, LINK, HOME, and optionally, OMPROUTE configuration statements or BSDROUTINGPARMS statements for IPv4 Static VIPAs or INTERFACE statements for IPv6 Static VIPAs.
Using the SOURCEVIPA configuration option, static VIPAs can be used as the source IP address for outbound datagrams for TCP, RAW, UDP (except routing protocols), and ICMP requests. For IPv6 static VIPAs to be used as source addresses, the SOURCEVIPA configuration option must be enabled and the VIPA interface must appear on the SOURCEVIPAINT keyword on some other INTERFACE statement. This provides tolerance of device and adapter failures for connection requests originating at a z/OS TCP/IP stack.
They can be specified as the source IP address for outbound TCP connection requests for all applications using this stack with TCPSTACKSOURCEVIPA.
They can be specified as the source IP address for outbound TCP connection requests for specific jobs or specific destinations through the use of the SRCIP profile statement block.
The number of static VIPAs on a stack is limited only by the range of host IP addresses that are available for that host.
They can be moved to a backup stack after the original owning stack has failed, by using VARY TCPIP,,OBEYFILE command processing to configure the VIPA on the backup stack and updating the routers.

Dynamic VIPAs have the following characteristics:

They can be configured to be moved dynamically from a failing stack to a backup stack within the same sysplex without operator intervention or external automation.
They can be moved manually by deactivating or reactivating them with the VARY TCPIP,,SYSPLEX operator command.
They can be dynamically activated by an application program.
They can distribute connections within a sysplex.
They can be specified on a TCPSTACKSOURCEVIPA statement. This allows a user to specify one VIPA to be used as the source IP address for outbound datagrams for TCP-only requests.
They can be specified as the source IP address for outbound TCP connection requests for specific jobs or specific destinations by using the SRCIP profile statement block.
Unlike static VIPAs, dynamic VIPAs:
- Are limited to 1024 per stack.
- Cannot be specified as the VIPA used by Enterprise Extender for connectivity purposes. (See Configuring static VIPAs for Enterprise Extender for details.)

Distributed DVIPAs have the following characteristics:

They have all the characteristics of DVIPAs, except that they cannot be dynamically activated by an application program.
One stack defines a DVIPA and advertises its existence to the network. Stacks in the target distribution list activate the DVIPA and accept connection requests.
Connection workload can be distributed across several stacks.

See Configuring distributed DVIPAs — sysplex distributor for more detailed descriptions.

Guideline: OSA-Express devices have a limit on the number of IP addresses (both IPv4 and IPv6 addresses) that can be registered to the device. The limit is dependent on the microcode level of the OSA-Express device. This limit applies across all TCP/IP stacks that share the OSA-Express device. When defining a large number of VIPAs, take care not to exceed this limit. If the limit is exceeded, IP addresses beyond the limit will not be registered with the OSA-Express devices, and incoming packets with those IP addresses will not be routed to the correct stack unless that stack is designated as the primary router.