Oracle : Troubleshoot ORA-12537

If you experience ORA-12537 connection closing after you opened firewall properly, you should check contents of protocol.ora file placed in Oracle Server.Generally, you can find it at "$ORACLE_HOME/network/admin/protocol.ora".

tcp.validnode_checking = yes
tcp.invited_nodes=( 192.168.0.100 )

Above config means, 152.68.18.73 is the only IP address which has authority to contact this Oracle Server. Be careful not to miss add server own IP address should be here.

tcp.validnode_checking = yes
tcp.excluded_nodes= (192.168.0.100 )

If you set any IP address into tcp.excluded_nodes item, that IP will be blocked when try to connect Oracle Server. Surely, you can use invited and excluded nodes with in same protocol.ora file simultaneously. When you need to allow more IP addresses, you can describe IP addresses in one line with comma seperation.

tcp.validnode_checking = yes
tcp.invited_nodes=( 192.168.0.100, 192.168.0.101 )

If you have so many IP addresses to allow or block, you can use IP range like 192.168.0.0 (B-Class). And you also can use domain name to describe specific IP address. Let`s see below example.

tcp.validnode_checking = yes
tcp.invited_nodes=( 192.168.0.100, 192.168.0.101, 192.168.0.0 )

Once you change on protocol.ora file, you should restart Oracle listener to make it effective.

- NoPD -