Software availability

The example ZOS Company data center contains components that contribute to software availability.

OSPF. The environment is running the OSPF routing protocol. Some organizations may use other routing protocols such as RIP. OSPF is a link state routing protocol; it runs on routers. Under z/OS, OSPF is implemented by running an application (started task) called OMPROUTE. If OSA-E1 became unavailable on LPAR1, OSPF detects this and would send all LPAR1 traffic through OSA-E2 until OSA-E1 is restored. OSPF within a mainframe data center environment is normally configured as a stub area. This is done to block external route and summary route information from being propagated down to z/OS, which only needs to know about adjacent routes.
TCP/IP. Each LPAR TCP/IP stack normally has allocated what is known as a virtual IP address (VIPA). A VIPA address is not tied to any physical interface, so it will never fail. Applications and network hosts are normally configured to target the VIPA addresses. VIPAs can be configured to move manually or dynamically. For example, LPAR2 could take over a VIPA address on LPAR1, and users would not lose their connections and would not be aware of the path change. VIPAs are a key component in providing high availability solutions for organizations.
VTAM. There are many functions within a z/OS VTAM environment that can be configured to aid in the recovery or the takeover of resources in the event of an outage.