Dynamic virtual addressing

The sysplex has been identified as a tightly-coupled cluster of computers with some workload balancing capabilities added for good measure. But how does the IP network take advantage of all this technology? The first part of the answer is the dynamic virtual IP address, or DVIPA.

Why DVIPA? For the network, DVIPA has these benefits:

Availability. DVIPAs allow servers to be made available independently of hardware or software failures. This can be done dynamically by TCP/IP or even by a system automation product.
Single image. DVIPA allows multiple LPARs to appear to be a single, highly available network host. Because DVIPA movement is automatic, end users and clients might never know a DVIPA address movement has occurred.
Application movement. With DVIPA, applications can be seamlessly moved from one LPAR to another, allowing a virtualization of the application itself.

DVIPA is part of the evolution of the VIPA feature. VIPA is defined through a DEVICE and LINK statement pair and remains unchanged unless explicitly removed by changing the active configuration statements. By contrast, a dynamic VIPA would normally be activated in one of two different ways:

An application explicitly issuing a bind() function call to the IP address. This is called unique application-instance DVIPA.
A TCP/IP stack dynamically activating the address. This is called multiple application-instance DVIPA.

In order for TCP/IP to communicate DVIPA status among LPARs, TCP/IP uses an XCF group called EZBTCPCS.