Oracle Database Listener TCP Validation

https://blog.dbi-services.com/oracle-12cr2-dataguard-and-tcp-valid_node_checking/

Standalone $ORACLE_HOME/network/admin
NAMES.DIRECTORY_PATH= (TNSNAMES, ONAMES, HOSTNAME, EZCONNECT)

SQLNET.ALLOWED_LOGON_VERSION_SERVER = 11
ADR_BASE = /usr2/app/oracle
tcp.validnode_checking = yes
#tcp.invited_nodes = (8.5.2.163, 8.5.2.7,)
tcp.invited_nodes = (127.0.0.1, 8.5.2.163, 8.5.2.7, 8.5.19.50)
tcp.excluded_nodes = (8.5.2.165)

RAC $GRID_HOME/network/admin

NAMES.DIRECTORY_PATH= (TNSNAMES, ONAMES, HOSTNAME, EZCONNECT)

SQLNET.ALLOWED_LOGON_VERSION_SERVER = 11
ADR_BASE = /usr2/app/oracle
tcp.validnode_checking = yes
# in subnet fasion:
#tcp.invited_nodes = (8.5.2.163/24, 8.5.2.7/24,)
tcp.invited_nodes = (127.0.0.1, 8.5.2.163, 8.5.2.7, 8.5.19.50)
tcp.excluded_nodes = (8.5.2.165)