ORA-12547: TNS:lost contact

Some time we come across the issue when trying to connect with database from the application side using apps as a user. This basically requires the listener to be up to make connection with database. We get error similar to
Cannot login to sqlplus using following userid/passwd.

sqlplus apps/apps@dbname.

Gives error
ORA-12547: TNS:lost contact
Error Messages:
ORA-12547: TNS:lost contact

In this case first check if the database listener is up or now. If the listener is up then check the sqlnet.ora file present in ORACLE_HOME/network/admin also can be reached using the environment variable TNS_ADMIN. This file contains 2 parameters, which restricts login to the database from the other hosts.

tcp.validnode_checking = yes

tcp.invited_nodes=(hostname1, hostname2, … )

This will allow entry from hostname1, hostname2 servers only. So if these values are commented and listener is bounced then this will resolve the issue.


  1. Thanks for your good paper.
    how to set up and using the environment variable TNS_ADMIN?

    My database is 64 bit 10gR2 4 node rac in linux and client side is 10gr2 in window 64 bit 2008.
    I could connect into other window single instance database. But I could not connect to Linux
    RAC database one instance
    with lost connect message.



  2. My sqlnet.ora file does not have tcp.validnode_checking = yes

    tcp.invited_nodes=(hostname1, hostname2, … ) these values.
    I set the TNS_ADMIN path but my problem is not resolved..


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