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Client Connection to RAC Intermittently Fails-ORA-12545

Whe LOCAL_LISTENER is not set at all or is not set correctly, PMON can register both the VIP hostname and the physical hostname with the REMOTE_LISTENER.  This is incorrect in RAC but if it does occur, the client can intermittently be routed to a listener endpoint on either of these addresses.  If the client is unable to resolve the physical hostname or even the vip hostname, the connection will fail with ORA-12545.
And important first set is to check the output for :  lsnrctl services <listener_name>
You should not see the physical hostname in the handler information for your RAC instances.   Here’s an example of an incorrect lsnrctl services <listener_name> output for a 2-node RAC cluster:
lsnrctl services oracle_rac_listener 
Service "oracle.oracle.com" has 2 instance(s). 
Instance "orcl1", status READY, has 2 handler(s) for this service... 
Handler(s): 
"DEDICATED" established:0 refused:0 state:ready 
REMOTE SERVER 
(ADDRESS=(PROTOCOL=TCP)(HOST=myphysicalhost1)(PORT=1521)) 
"DEDICATED" established:326 refused:0 state:ready 
LOCAL SERVER 

Instance "orcl2", status READY, has 1 handler(s) for this service... 
Handler(s): 
"DEDICATED" established:394371 refused:0 state:ready 
REMOTE SERVER 
(ADDRESS=(PROTOCOL=TCP)(HOST=myphysicalhost2)(PORT=1521)) 
Here’s an example of what it ought to look like when LOCAL_LISTENER is configured correctly:
lsnrctl services oracle_rac_listener 
Service "oracle.oracle.com" has 2 instance(s). 
Instance "orcl1", status READY, has 2 handler(s) for this service... 
Handler(s): 
"DEDICATED" established:0 refused:0 state:ready 
REMOTE SERVER 
(ADDRESS=(PROTOCOL=TCP)(HOST=myVIP_host1)(PORT=1521)) 
"DEDICATED" established:326 refused:0 state:ready 
LOCAL SERVER 

Instance "orcl2", status READY, has 1 handler(s) for this service... 
Handler(s): 
"DEDICATED" established:394371 refused:0 state:ready 
REMOTE SERVER 
(ADDRESS=(PROTOCOL=TCP)(HOST=myVIP_host2)(PORT=1521))
Log in with privileges to the instance and issue the following commands so that LOCAL_LISTENER is set correctly:
alter system set LOCAL_LISTENER="(address=(protocol=tcp)(port=1521)(host=<your_vip_node1>)) scope=both sid='INSTANCE_NAME1';
Do the same for the 2nd instance where host is set to the <vip_host_node2> and the sid is set to the 2nd instance name.
alter system set LOCAL_LISTENER="(address=(protocol=tcp)(port=1521)(host=<your_vip_node2>)) scope=both sid='INSTANCE_NAME2';
Now the correct address using the VIP hostname will be registered against the listeners in the cluster.
The client should be able to resolve all forms of the VIP host via their /etc/hosts file.  i.e. short name and fully qualified.

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