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Manual Chapter: Defining Links
Manual Chapter
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Before you can load balance inbound and outbound traffic on the Link Controller system, you must add at least one link. A link is a network device that connects your internal network with the Internet.
To add a link to the Link Controller system, you must configure certain basic properties. These properties include settings such as the router address of the link, as well as the limit thresholds for inbound and outbound traffic. After you establish these basic properties, you can further customize the link through a variety of advanced configuration options.
One of the most critical aspects of adding links to the Link Controller system is adding each link to a specialized group within the system, called the default gateway pool. The Link Controller system uses this pool to load balance network traffic that is moving between your private network and the Internet at large.
Note: If your environment requires that the Link Controller system operate in a fail-safe or high availability mode, see Chapter 16, Configuring High Availability, in the TMOS® Management Guide for BIG-IP® Systems.
Links form the backbone of the Link Controller system configuration, as they determine how traffic enters and leaves your network. The load balancing features of the Link Controller system require at least two links; however, you can add as many links as you need to manage your inbound and outbound traffic.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
2.
Click the Create button.
3.
In the Name box, type a name for the link.
Note: The link name is limited to 63 characters.
4.
For the Router Address List setting, in the Address box, type the IP address that is defined as a member of the default gateway pool. This IP address is also considered the IP address assigned to the router that belongs to the local area network.
5.
In the Uplink Address box, type the IP address that identifies the router on the wide-area network. The Link Controller system uses this address to obtain SNMP statistics from the routers WAN interface.
6.
In the Service Provider box, type the name of the Internet Service Provider.
7.
For the Health Monitors setting that the Link Controller system uses to determine the availability of the link:
b)
Use the Move [<<] button to add the monitor to the Enabled list.
F5 Networks recommends that you add at least the bigip_link and snmp_link monitors.
8.
Click the Create button to save your changes.
A health monitor is a software utility that tracks the performance and availability of a given link. The Link Controller system uses health monitors to ensure that is it selecting the best link when load balancing network traffic. You can add a health monitor when you first configure a link, or you can add it at a later time. For more detailed information on monitors, including how to configure the properties of existing monitors or create a custom monitor for your configuration, see Chapter 8, Configuring Monitors.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
For the Health Monitors setting, select the appropriate monitors from the Available list, then use the Move [<<] button to move these monitors to the Enabled list.
If you are unsure as to which monitors you should add to the link, F5 Networks recommends that you assign at least the bigip_link and snmp_link monitors.
4.
Click the Update button to save your changes.
One of the first monitors you should add to any link is the bigip_link monitor. This monitor is responsible for gathering metrics and statistical data that the Link Controller system gathers from other monitors that are verifying the availability of other network resources and services.
For example, the IT department at the fictional company, SiteRequest, is using an FTP and HTTP monitor to track the health of a web server. In addition to these monitors, the IT department also assigns the bigip_link monitor, which accumulates the data the FTP and HTTP monitors gather, allowing the IT department to view statistical and health information on the web server through the Configuration utility.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
For the Health Monitors setting, select the appropriate monitors from the Available list, then use the Move [<<] button to move these monitors to the Enabled list.
4.
Click the Update button to save your changes.
Another option when determining how to monitor the health of a network resource, such as a web server, is to use the Simple Network Management Protocol, or SNMP. Tracking the health of a resource through SNMP requires that you:
Assign the snmp_link monitor to the given resource in the Configuration utility.
The snmp_link monitor is a specialized health monitor that acquires SNMP data that a given resource sends, and makes that information available to you through the Configuration utility.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
For the Health Monitors setting, select snmp_link from the Available list, then use the Move [<<] button to move the monitor to the Enabled list.
4.
Click the Update button to save your changes.
By default, the Link Controller system requires that all health monitors assigned to a resource verify that the resource is available for load balancing traffic. However, you can configure the Link Controller system so that only a certain number of monitors must verify that the link is available.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
From the Configuration list, select Advanced.
4.
From the Availability Requirements list, select the number of monitors that must identify the link as available.
Select All to require that all monitors identify the link as available.
Select At Least to specify a minimum number of monitors that must identify the link as available.
5.
Click the Update button to save your changes.
Often, the links that you want to manage with the Link Controller system have bandwidth restrictions that you want to maintain to ensure that your network is operating in a cost-effective manner. Through the Link Controller system, you can establish bandwidth restrictions for each link. When the traffic on a link exceeds a specified value, the system marks the link as unavailable, and attempts to use another link.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
From the Configuration list, select Advanced.
4.
For the Traffic Limits setting, specify the Inbound, Outbound, and Total Traffic Limits. For each option, you have two choices:
None, which instructs the Link Controller system to ignore this statistic when determining load balancing options.
Up to, which allows you to specify a value, in megabits per second, that denotes the maximum amount of traffic of that type for the link.
5.
Click the Update button to save your changes.
With the link weighting and billing properties, you can refine the link load balancing and statistics reporting for the links in your configuration. On the Link Weighting screen, you determine how the Link Controller system manages and distributes traffic across the links, using the following settings.
Duplex Billing
If your ISP uses duplex billing, you can set the Duplex Billing option so that the statistics and billing report screens accurately reflect the bandwidth usage for the link. Note that by default, the duplex billing setting is on.
Price Weighting
If you want the Link Controller system to load balance traffic based on the cost of the bandwidth, then select the Use Price Weighting option. You can use this weighting option to avoid the costs associated with exceeding your prepaid bandwidth. You can also use this weighting option to direct traffic over the least expensive link first.
Ratio Weighting
If you want the Link Controller system to load balance the total traffic to the controller based on a ratio, then select the Use Ratio Weighting option. When you have links of varying bandwidth sizes, you can use this weighting option to avoid oversaturating a smaller link with too much traffic.
Important: You can use either the price weighting option or the ratio weighting option to load balance your link traffic for all of your links. You cannot use both options. Regardless of which weighting option you use, you must use the same weighting option for all links.
Certain ISPs employ duplex billing when managing the costs of an Internet connection. Duplex billing refers to a billing method in which the current traffic rate is considered to be the maximum of either the inbound or outbound traffic. By default, any links that you add in the Link Controller system have the Duplex Billing option enabled.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
From the Configuration list, select Advanced.
4.
Check Duplex Billing, located at the bottom of the screen.
5.
Click the Update button to save your changes.
You can set the price weighting that you want the Link Controller system to use when load balancing link traffic. The price weighting is based on the billing structure that your ISP uses. The Link Controller system load balances traffic to another link if the lowest cost link reaches a threshold that you have set. This helps you control traffic based on the cost the ISP is charging for the bandwidth.
Warning: If you configure price weighting for one link on the Link Controller system, you must configure price weighting for all of the remaining links in the configuration. If you do not, the Link Controller system load balances only to the link for which price weighting is defined.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
From the Configuration list, select Advanced.
4.
From the Weighting list, select Price (Dynamic Ratio).
In the Prepaid Segment box, type the maximum bandwidth usage you pay for each month. For example, if your ISP charges $1000 for bandwidth usage in the 0 to 1.54 bps range, type 154. That means that you pay every month for up to 1.54 bps even if you do not use the link at all.
For the Incremental Segments setting, type the bandwidth (in bps) and the associated cost of the next pricing tier. For example, if your ISP charges $2200 for bandwidth usage in the 1.54 to 3 Mbps range, type 300 in the Up to box and 2200 in the cost box. Click the Add button to add the new cost tier to the configuration. You can add additional cost tiers to the configuration if required.
6.
Click the Update button to save your changes.
In a configuration in which you have multiple links available to handle inbound and outbound traffic, it is not uncommon for the Link Controller system to determine that one or more links are valid options for load balancing traffic. You can control how the system handles this situation by assigning a link ratio weight for each link. When multiple links are available to handle traffic, the Link Controller system selects a link based on the values of the link ratios of each link.
For example, the fictional company, SiteRequest, has two links available for handling network traffic during business hours. One link is a T1 line, while the other is a DSL line. To ensure their network traffic flows efficiently, the IT team at SiteRequest sets the link ratio value for the T1 link to 2 and the link ratio value for the DSL link to 1. This configuration instructs the Link Controller system to send twice as much traffic through the T1 link as through the DSL link.
If you want to load balance link traffic using link ratio weighting, you need to configure the following settings in addition to specifying the ratio weight on the link.
Inbound load balancing
The inbound load balancing mode, on a wide IP, is Quality of Service. All QOS coefficients should be set to 0, except for the Link Capacity coefficient, which should be any number other than 0.
Outbound load balancing
The outbound load balancing mode, for a router pool (usually the default gateway pool), is Dynamic Ratio.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
3.
From the Configuration list, select Advanced.
4.
In the Link Ratio box, type a link ratio value.
5.
Click the Update button to save your changes.
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