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Establishing Remote Connection in Oracle

The following images illustrate the flow between the client and the remote database in establishing a remote connection.

The SQL statement
select * from customer@rdb
specified rdb as a DATABASE LINK

The link name rdb is looked up in the Oracle dictionary DBA_DB_LINK table to get the remote USER ID, PASSWORD, and the TNS service name

The TNS service name is used as input to the tnsnames.ora.file. The tnsnames.ora file provides the PROTOCOL, the HOST_NAME, and the ORACLE_SID.

The HOST_NAME is used as input to the UNIX hosts file, where the IP_ADDRESS is collected.

The IP_ADDRESS, PROTOCOL, ORACLE_SID, USER_ID, PASSWORD are packaged and sent as a network packet to the remote Oracle listener