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Overview of Connecting to Oracle Database Using Services and VIP AddressesAll nodes in an Oracle RAC environment must connect to a Local Area Network (LAN) to enable users and applications to access the database. Applications should use the Oracle Database services feature to connect to an Oracle database. Services enable you to define rules and characteristics to control how users and applications connect to database instances. These characteristics include a unique name, workload balancing and failover options, and high availability characteristics. Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.Users can access an Oracle RAC database using a client/server configuration or through one or more middle tiers, with or without connection pooling. Users can be database administrators, developers, application users, power users, such as data miners who create their own searches, and so on.Most public networks typically use TCP/IP, but you can use any supported hardware and software combination. Oracle RAC database instances should be accessed through the Single Client Access Name (SCAN) for the cluster.See Also:"Overview of Automatic Workload Management" for more information about SCANsThe interconnect network is a private network that connects all of the servers in the cluster. The interconnect network uses a switch (or multiple switches) that only the nodes in the cluster can access. Configure User Datagram Protocol (UDP) on a Gigabit Ethernet for your cluster interconnect. On Linux and UNIX systems, you can configure Oracle Clusterware to use either the UDP or Reliable Data Socket (RDS) protocols. Windows clusters use the TCP protocol. Crossover cables are not supported for use with Oracle Clusterware interconnects.Note:Do not use the interconnect (the private network) for user communication, because Cache Fusion uses the interconnect for interinstance communication.If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections, but it does not accept connections to the Oracle database. Generally, VIP addresses fail over when:The node on which a VIP address runs failsAll interfaces for the VIP address failAll interfaces for the VIP address are disconnected from the networkClients that attempt to connect to the VIP address receive a rapid connection refused error instead of waiting for TCP connect timeout messages. When the network on which the VIP is configured comes back online, Oracle Clusterware fails back the VIP to its home node where connections are accepted.If you use Network Attached Storage (NAS), then you are required to configure a second private network. Access to this network is typically controlled by the vendor's software. The private network uses static IP addresses.Oracle RAC 11g release 2 (11.2) supports multiple public networks. Each network has its own subnet and each database service uses a particular network to access the Oracle RAC database. Each network is a resource managed by Oracle Clusterware.You must also create a SCAN for each cluster, which is a single network name defined either in your organization's Domain Name Server (DNS) or in the Grid Naming Service (GNS) that round robins to three IP addresses. Oracle recommends that all connections to the Oracle RAC database use the SCAN in their client connection string. Incoming connections are load balanced across the active instances providing the requested service through the three SCAN listeners. With SCAN, you do not have to change the client connection even if the configuration of the cluster changes (nodes added or removed).
Overview of Connecting to Oracle Database Using Services and VIP Addresses