SCAN listener in RAC

SCAN listeners are remote listeners and act as a forefront of connection management, applications connect to SCAN listeners.
and SCAN listeners act as a conduit mechanism to forward connections to an instance that can provide better quality of service.

When a client submits a connection request, the SCAN listener listening on a SCAN IP address
and the SCAN port are contacted on the client’s behalf. Because all services on the cluster are
registered with the SCAN listener, the SCAN listener replies with the address of the local
listener on the least-loaded node where the service is currently being offered.

During installation, listeners are created on nodes for the SCAN IP addresses.

To check the status of SCAN listener use the command lsnrctl status < scan listener name>

For example:

grid@dbsrv:/u01/app/12.1.0/grid/network/admin$ lsnrctl status  LISTENER_SCAN1
   LSNRCTL for Solaris: Version 12.1.0.2.0 - Production on 05-SEP-2022 16:58:18
   Copyright (c) 1991, 2014, Oracle.  All rights reserved.
   Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1)))
  STATUS of the LISTENER
  ------------------------
  Alias                     LISTENER_SCAN1
  Version                   TNSLSNR for Solaris: Version 12.1.0.2.0 - Production
  Start Date                01-SEP-2022 03:47:55
  Uptime                    4 days 13 hr. 10 min. 23 sec
  Trace Level               off
  Security                  ON: Local OS Authentication
  SNMP                      OFF
  Listener Parameter File   /u01/app/12.1.0/grid/network/admin/listener.ora
  Listener Log File         /u01/app/grid/diag/tnslsnr/wgpdbsrv1/listener_scan1/alert/log.xml
  Listening Endpoints Summary...
    (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER_SCAN1)))
    (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=10.02.10.10)(PORT=1521)))
  Services Summary...
  Service "dbprod" has 1 instance(s).
    Instance "dbprod1", status READY, has 2 handler(s) for this service...
  Service "dbprodXDB" has 1 instance(s).
    Instance "dbprod1", status READY, has 1 handler(s) for this service...
  The command completed successfully

And  to check the services of the SCAN listener use lsnrctl services  < scan listerner name>

Example:

grid@dbsrv:/u01/app/12.1.0/grid/network/admin$ lsnrctl services  LISTENER_SCAN1
    LSNRCTL for Solaris: Version 12.1.0.2.0 - Production on 05-SEP-2022 17:01:57
    Copyright (c) 1991, 2014, Oracle.  All rights reserved.
    Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1)))
   Services Summary...
   Service "dbprod" has 1 instance(s).
     Instance "dbprod1", status READY, has 2 handler(s) for this service...
    Handler(s):
      "DEDICATED" established:1262 refused:0 state:ready
      REMOTE SERVER
      (ADDRESS=(PROTOCOL=TCP)(HOST=10.02.10.44)(PORT=1521))
      "DEDICATED" established:1251 refused:0 state:ready
      REMOTE SERVER
      (ADDRESS=(PROTOCOL=TCP)(HOST=10.02.10.44)(PORT=1521))
   Service "dbprodXDB" has 1 instance(s).
     Instance "dbprod1", status READY, has 1 handler(s) for this service...
    Handler(s):
      "D000" established:0 refused:0 current:0 max:1022 state:ready
      DISPATCHER <machine: dbsrv, pid: 7778>
      (ADDRESS=(PROTOCOL=tcp)(HOST=dbsrv.abc.com)(PORT=45000))
   The command completed successfully

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