About the SCAN

During the installation of Oracle Grid Infrastructure, several Oracle Clusterware resources are created for the SCAN.

  • A SCAN virtual IP (VIP) is created for each IP address that Oracle Single Client Access Name (SCAN) resolves to

  • A SCAN listener is created for each SCAN VIP

  • A dependency on the SCAN VIP is configured for the SCAN listener

SCANs are defined using one of two options:

  • The SCAN is defined in DNS

    If you configure a SCAN manually, and use DNS for name resolution, then your network administrator should create a single name for the SCAN that resolves to three IP addresses on the same network as the public network for the cluster. The SCAN name must be resolvable without the domain suffix (for example, the address sales1-scan.example.com must be resolvable using sales1-scan). The SCAN must not be assigned to a network interface, because Oracle Clusterware resolves the SCAN.

    The default SCAN is cluster_name-scan.domain_name. For example, in a cluster that does not use GNS, if your cluster name is sales1, and your domain is example.com, then the default SCAN address is sales1-scan.example.com:1521.

  • The SCAN is defined in GNS

    When using GNS and DHCP, Oracle Clusterware configures the VIP addresses for the SCAN name that is provided during cluster configuration. The node VIP and the three SCAN VIPs are obtained from the DHCP server when using GNS. If a new server joins the cluster, then Oracle Clusterware dynamically obtains the required VIP address from the DHCP server, updates the cluster resource, and makes the server accessible through GNS.

Oracle recommends that you configure clients connecting to the cluster to use the SCAN name. Clients connecting to Oracle RAC databases using SCANs do not have to be configured with addresses of each node that hosts a particular database or database instance. For example, if you configure policy-managed server pools for a cluster, then connecting to the database using a SCAN enables connections to server pools in that database, regardless of which nodes are allocated to the server pool. You can add or remove nodes from the database without having to reconfigure clients connecting to the database.