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Manual Chapter: Controlling Load Balancing Costs
Manual Chapter
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You can configure the BIG-IP® Link Controller to use cost-based load balancing to manage the traffic flowing in and out of a network. In cost-based load balancing, you prioritize link usage based on the cost of the bandwidth for that connection to the Internet. The Link Controller sends traffic to the link that is currently operating at the lowest cost. As the usage cost for each link changes, the Link Controller dynamically shifts traffic to the best link.
Weighting
The Weighting option for each link determines how the Link Controller prioritizes the links in its configuration. By default, this option is set to Ratio. For cost-based load balancing, however, you must set this option to Price (Dynamic Ratio).
Prepaid Segment
Most Internet Service Providers (ISPs) offer bandwidth plans that include a prepaid amount of bandwidth. In the Prepaid Segment option, you assign the appropriate bandwidth and cost values that are prepaid for the link.
Incremental Segments
The Incremental Segment option allows you to define the cost per segment values that apply to this link. You can assign as many incremental segments as needed.
Note: When implementing cost-based load balancing, it is important that your configuration applies to all of the links that the Link Controller manages. For example, F5 Networks does not recommend applying cost-based load balancing to one set of links and ratio load balancing to another set.
Figure 3.1 depicts the cost-base load balancing process. In this process the following sequence occurs:
3.
The Link Controller determines the best link based on current cost estimates and bandwidth usage, and sends the appropriate response back to the LDNS server.
5.
The client then communicates with the appropriate virtual server through the corresponding link that the Link Controller specified.
To illustrate how cost-based load balancing works, consider the fictional company SiteRequest. This company has two links for managing its inbound and outbound traffic:
Link Alpha, which is the primary link for the network. This link uses an ISP to which a flat fee of $45 is paid for up to 4Mbps of total (both inbound and outbound) traffic. If the limit of 4Mbps is exceeded, SiteRequest incurs a $2/Mbps charge.
Link Beta, which is a secondary link for the network. This link uses an ISP with which SiteRequest does not have a prepaid amount of bandwidth. Instead, SiteRequest is billed based on a pay-as-you-go basis. The rate charged for using this link is set at $1/Mbps.
As these rates illustrate, the most cost-efficient configuration for SiteRequests links is to have Link Alpha handle traffic until it reaches 4Mbps, then send any traffic over 4Mbps to Link Beta. When the traffic decreases, the Link Controller must switch back to using only Link Alpha again.
Table 3.1 provides additional information about each link.
Router Address
Uplink Address
The first task to implement a Link Controller configuration that uses cost-based load balancing to manage outbound traffic is to add and configure the links on the Link Controller.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
2.
Click Create.
3.
In the Name box, type the name of the link.
For this example, type Link Alpha.
4.
In the Router Address box, type the IP address of the router in the Address box.
For this example, type 192.168.5.5.
5.
In the Uplink Address box, type the IP address that corresponds with the external Internet connection.
For this example, type 192.168.5.6.
6.
In the Service Provider box, type the name of the ISP provider.
For this example, select Global ISP.
7.
From the Configuration list, select Advanced.
8.
From the Weighting list, select Price (Dynamic Ratio).
9.
In the Prepaid Segment box, type the amount of bandwidth that is prepaid for the link.
For this example, type 4000.
10.
For the Incremental Segments setting, add the incremental segment price.
For this example type the following entry:
Up to 1000 bps at 2 $/Mbps
11.
Click Create.
Repeat this procedure to add the second link to the configuration. In this example, when you add the second link, accept the default Weighting value of Ratio, set the Prepaid Segment option to 0 and add the following entry in the Incremental Segment option: Up to 1000 bps at 1 $/Mbps
After you add and configure the relevant links, the next task is to create the default gateway pool that load balances the traffic across the links.
1.
On the Main tab of the navigation pane, expand Local Traffic and then click Pools.
2.
Click Create.
3.
In the Name box, type the name of the pool.
For this example, type default_gateway_pool.
4.
In the Resources area, for the New Members setting, add the IP addresses associated with each link.
In this example type the following:
5.
Click Finished.
After you create a default gateway pool, you must instruct the Link Controller to use the pool as the default gateway connection between the internal network and the Internet.
1.
2.
Click Add.
3.
From the Type list, select Default Gateway.
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From the Resource list, select Use Pool.
5.
From the Pool list, select default_gateway_pool.
6.
Click Finished.
After creating the default gateway pool, configure the virtual servers, one for each link that load balances inbound connections across the servers. You also configure one wildcard virtual server to load balance outbound connections across the routers.
1.
On the Main tab of the navigation pane, expand Local Traffic and then click Virtual Servers.
2.
Click Create.
3.
In the Name box, type the name of the virtual server.
For this example, type VS for Link Alpha.
4.
For the Destination setting, select Host.
5.
In the Service Port box, type 80.
6.
Click Finished.
1.
On the Main tab of the navigation pane, expand Local Traffic and then click Virtual Servers.
2.
Click Create.
3.
In the Name box, type the name of the virtual server.
For this example, type outbound.
4.
For the Destination setting, in the Address box, type 0.0.0.0
5.
In the Service Port box, type 0.
6.
Click Finished.
The last task in this implementation is to configure a wide IP to which the Link Controller load balances incoming DNS requests.
1.
On the Main tab of the navigation pane, expand Link Controller and then click Inbound Wide IPs.
2.
Click Create.
3.
In the Name box, type the name of the wide IP
For this example, type www.siterequest.com.
4.
For the Load Balancing Method setting, make selections from the three lists. For this example:
Select Ratio from the Preferred list.
Select Round Robin from the Alternate list.
Select Return to DNS from the Fallback list.
5.
In the Member List setting, add the virtual servers that you created previously.
For this example, select the following from the Virtual Server list, and then click Add:
6.
Click Finished.
You now have a Link Controller configured to manage DNS traffic for www.siterequest.com. As data flows in and out of the network, the Link Controller monitors the total amount of bandwidth for each link. While traffic remains below 4Mbps, the Link Controller uses Link Alpha. If traffic exceeds that amount, the Link Controller sends the overflow traffic to Link Beta. If a link goes offline for any reason, the Link Controller uses the Alternate and Fallback load balancing modes to route traffic through an available link.
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