SCAN is a name that gives clients access to the cluster service. You can use cluvfy comp scan (found Grid_home \ bin) to verify that DNS correctly associates the SCAN with the addresses.
Because SCAN is associated with the cluster as a whole instead of a specific node, SCAN makes it possible to add or remove nodes from the cluster without reconfiguring clients. It also adds location independence for databases, so that the client configuration does not need to depend on which nodes run a particular database instance. Clients can still access the cluster as in previous versions, but Oracle recommends that clients accessing the cluster use SCAN.
After installation, when a client sends a request to the cluster, Oracle Clusterware SCAN listeners direct client requests to the servers in the cluster.
Use the following command to verify that SCAN and SCAN listeners are configured and running on all nodes in the cluster:
cluvfy comp scan [-verbose]
cluvfy comp scan
This command produces output similar to the following:
Verifying Single Client Access Name (SCAN) …
Verifying DNS/NIS name service ‘sp060-scan’ …
Verifying Name Service Switch Configuration File Integrity …PASSED
Verifying DNS/NIS name service ‘sp060-scan’ …PASSED
Verifying Single Client Access Name (SCAN) …FAILED (PRVF-5067)
Verification of SCAN was unsuccessful on all the specified nodes.
Failures were encountered during execution of CVU verification request “SCAN”.
Verifying Single Client Access Name (SCAN) …FAILED
sp060dbadm01: PRVF-5067 : TCP connectivity check for SCAN listener
“LISTENER_SCAN2” failed on node “sp060dbadm01”
TNS-12543: TNS:destination host unreachable
CVU operation performed: SCAN
Date: Nov 27, 2019 10:20:33 AM
CVU home: /u01/app/188.8.131.52/grid/