VIPA as the name suggest is a virtual IP address, that is, it is not associated with a physical (OSA) interface and is therefore available for the life of the TCP/IP stack, which in most organisations is the life of the mainframe LPAR.
Users and services (i.e. FTP) connect to the VIPA address, not the physical OSA addresses. When multiple adapters are installed, multiple ‘routes’ to the VIPA exist. Should one ‘route’ (adapter) fail the traffic transparently uses another route.
In the sysplex each zOS image has an IP address for each OSA and a static VIPA address for the image.
A dynamic VIPA address will route users to either side of the plex.
To get to either image use the dynamic VIPA address - failure on either side will route the user to the other. May need to logon again.
To get to a specific side use the static VIPA - if an OSA fails it routes via the other.
To get to a specific OSA use its IP address explicitly.
OSPF via OMPROUTE should broadcast addresses throught the network ou to the switches.