A common problem in Oracle 12c is, that ACLs are often not wanted to limit connections from database to other hosts. To disable ACLs is not that easy, so the best way is to enable connections and resolutions to all hosts for all users like following example:


BEGIN
DBMS_NETWORK_ACL_ADMIN.APPEND_HOST_ACE(
host => '*',
ace => xs$ace_type(privilege_list => xs$name_list('resolve'),
principal_name => 'PUBLIC',
principal_type => xs_acl.ptype_db));
DBMS_NETWORK_ACL_ADMIN.APPEND_HOST_ACE(
host => '*',
ace => xs$ace_type(privilege_list => xs$name_list('connect'),
principal_name => 'PUBLIC',
principal_type => xs_acl.ptype_db));
END;
/
COMMIT;

“*” in host parameter allows connection to all hosts, principal_name “PUBLIC” allows all users of the database to initiate network connections.