Connect To Oracle 12c CDB In RAC Environment

DB Name = ora12c
Instance Name = ora12c_1 (node 1) and ora12c_2 (node 2)

To connect to the multitenant container database ora12c instrance ora12c_1.
Execute . oraenv to switch to the appropriate system variable (ORACLE_SID and ORACLE_HOME) or you can set it manually.

[oracle@ora12cn1 ~]$ . oraenv
ORACLE_SID = [ora12c_1] ? ora12c_1
The Oracle base remains unchanged with value /u01/app/oracle
[oracle@ora12cn1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Thu Nov 21 14:48:40 2013
Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options

SQL>
SQL> 

Check if the database is a multitenant container database.

SQL> SELECT db.name "DB Name", i.instance_name "Instance Name", db.cdb, i.con_id
  2  FROM gv$database db, gv$instance i
  3  WHERE i.inst_id = db.inst_id;

DB Name   Instance Name    CDB   CON_ID
--------- ---------------- --- ----------
ORA12C    ora12c_1         YES 0

Extracted from Oracle 12c Document, CON_ID = 0 mean CDB. 

About Viewing Information When the Current Container Is the Root

When the current container is the root, a common user can view data dictionary information for the root and for PDBs by querying container data objects. A container data object is a table or view that can contain data pertaining to the following:

• One or more containers
• The CDB as a whole
• One or more containers and the CDB as a whole

Container data objects include V$, GV$, CDB_, and some Automatic Workload Repository DBA_HIST* views. A common user's CONTAINER_DATA attribute determines which PDBs are visible in container data objects.

In a CDB, for every DBA_ view, there is a corresponding CDB_ view. All CDB_ views are container data objects, but most DBA_ views are not.

Each container data object contains a CON_ID column that identifies the container for each row returned. Table 43-1 describes the meanings of the values in the CON_ID column.

Table 43-1 CON_ID Column in Container Data Objects

Value in CON_ID Column	Description
0	The data pertains to the entire CDB
1	The data pertains to the root
2	The data pertains to the seed
3 - 254	The data pertains to a PDB Each PDB has its own container ID.