13.1.2 About the Address List Parameters

When a database service is accessible by multiple listener protocol addresses, specify the order in which the addresses are to be used, such as chosen randomly or tried sequentially. The following table lists the parameters used with multiple protocol addresses.

Table 13-1 Address List Parameters in the tnsnames.ora File

Parameter	Description
FAILOVER	At connect time, this parameter instructs Oracle Net to fail over to a different listener if the first listener fails when set to on. The number of addresses in the list determines how many addresses are tried. When set to off, instructs Oracle Net to try one address. Connect-time failover is turned on by default for multiple address lists (ADDRESS_LIST), connect descriptors (DESCRIPTION), and multiple connect descriptors (DESCRIPTION_LIST).
LOAD_BALANCE	When set to on, this parameter instructs Oracle Net to progress through the list of protocol addresses in a random sequence, balancing the load on the various listeners. When set to off, instructs Oracle Net to try the addresses sequentially until one succeeds. Client load balancing is turned on by default for multiple connect descriptors (DESCRIPTION_LIST).
SOURCE_ROUTE	When set to on, this parameter instructs Oracle Net to use each address in the order presented until the destination is reached. This parameter is required for reaching the destination using a specific route, that is, by specific computers. This parameter is used to enable connections to Oracle Connection Manager.

Note:

You cannot set source routing (SOURCE_ROUTE) at the same level as connect-time failover (FAILOVER) or client load balancing (LOAD_BALANCE). Source routing connects to each address in the list sequentially whereas connect-time failover and client load balancing select a single address from a list.

When a connect descriptor in a tnsnames.ora file contains at least two protocol addresses for an Oracle Connection Manager hop, then parameters for connect-time failover and load balancing within the hop can be included in the file.

The following table describes the address list options.

Table 13-2 Address List Options Dialog Box

Option	Parameter Setting
Try each address, in order, until one succeeds.	FAILOVER=on
Try each address, randomly, until one succeeds.	LOAD_BALANCE=on FAILOVER=on
Try one address, selected at random.	LOAD_BALANCE=on
Use each address in order until destination reached.	SOURCE_ROUTE=on
Use only the first address.	LOAD_BALANCE=off FAILOVER=off SOURCE_ROUTE=off

The following example shows a tnsnames.ora file configured for client load balancing:

sales.us.example.com=
 (DESCRIPTION=
  (ADDRESS_LIST=
  (LOAD_BALANCE=on)
   (ADDRESS=(PROTOCOL=tcp)(HOST=sales1-server)(PORT=1521)) 
   (ADDRESS=(PROTOCOL=tcp)(HOST=sales2-server)(PORT=1521)))
  (CONNECT_DATA=
    (SERVICE_NAME=sales.us.example.com))) 

The following example shows a tnsnames.ora file configured for connect-time failover:

sales.us.example.com=
 (DESCRIPTION=
  (ADDRESS_LIST=
   (LOAD_BALANCE=off)
   (FAILOVER=on)
   (ADDRESS=(PROTOCOL=tcp)(HOST=sales1-server)(PORT=1521)) 
   (ADDRESS=(PROTOCOL=tcp)(HOST=sales2-server)(PORT=1521)))
  (CONNECT_DATA=
   (SERVICE_NAME=sales.us.example.com)))

The following example shows a tnsnames.ora file configured for Oracle Connection Manager and load balancing:

sales.us.example.com=
(DESCRIPTION=
   (SOURCE_ROUTE=ON)
   (ADDRESS=(PROTOCOL=tcp)(HOST=cman-pc1)(PORT=1630))
   (ADDRESS=
     (LOAD_BALANCE=ON)
     (ADDRESS=(PROTOCOL=tcp)(HOST=cman-pc2)(PORT=1521))
     (ADDRESS=(PROTOCOL=tcp)(HOST=cman-pc3)(PORT=1521)))
   (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com)))

• Configuring Address List Parameters
  

See Also:

"Configuring Clients for Oracle Connection Manager" for additional information about configuring clients for source routing

13.1.2.1 Configuring Address List Parameters

The following procedure describes how to configure address list parameters:

1. Perform the procedure in "Creating a List of Listener Protocol Addresses".

2. Use Oracle Enterprise Manager Cloud Control or Oracle Net Manager to configure address list options.

   • For Oracle Enterprise Manager Cloud Control, select the appropriate option in the Connect-time Failover and Client Load Balancing section.

   • For Oracle Net Manager, click Advanced in the Address Configuration box. The Address List Options dialog box appears. Select the appropriate option.