OUTBOUND_DBLINK_PROTOCOLS  specifies the network protocols allowed for communicating for outbound/outgoing database links in the database. It is introduced in Oracle 12.2 release.

Possible values – { ALL | NONE | [ TCP | [, ] | TCPS | [, ] | IPC ] }

By default, the value is set to ALL. i.e User can fetch data using db_link.

For better understanding, let’s check the below example.

With OUTBOUND_DBLINK_PROTOCOLS=ALL

So with this default setting, db_links are working fine as usual.

Now let’s alter this and set it to NONE:

With OUTBOUND_DBLINK_PROTOCOLS= NONE

Now i tried to access the previously created db_link:

it is not allowed as expected. What about creating a new DB_LINK.

Well create database link also not allowed.

Conclusion:

We can say, this parameter is introduced as a security feature in Oracle 12.2 release. This will control the outbound database_link access.