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Manual Chapter: Working with Topologies
Manual Chapter
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10 
The Link Controller system handles name resolution requests at an international level. Consequently, one of the methods you can employ to load balance requests is through the use of topologies. A topology is a set of characteristics that identifies the origin of a given name resolution request. In the Link Controller system, topologies belong to one of several categories, including:
A region is a customized collection of topologies. For example, you could create a topology for each of a number of ISPs in Denmark, Iceland, Finland, Norway, and Sweden. These topologies could then compose a custom region called Scandinavia.
Through topologies, you can instruct the Link Controller system to select a resource based on its physical proximity to the client making the name resolution request. This process helps ensure that name resolution requests are answered and managed in the fastest possible time.
You can instruct the Link Controller system to use topologies to load balance name resolution requests across virtual servers at the wide IP level.
A fictional company, SiteRequest, allows its customers to download applications from its web site. SiteRequest has three major customers, one each in New York, Paris, and Tokyo. To ensure that customers can download their purchased application as quickly as possible, the IT department has decided to create topologies with which to load balance name resolution requests.
SiteRequest has created a custom region named Paris to handle the name resolution requests originating in Paris. SiteRequest has assigned the IP subnet 192.168.15.2 of the SiteRequest network as the destination for the requests from Paris. With this custom region created, the next step is to create a topology record for the Link Controller system. A topology record is a statement that tells the system how to handle name resolution requests based on topologies. In this case, the IT department creates the record as follows:
The final step to implement this topology is to configure the corresponding wide IP, www.siterequest.com, to use topology load balancing. See Using topology load balancing in a wide IP, for more information.
2.
Click Topology.
The Topology Records screen opens.
A topology record has several elements: a request source statement, a destination statement, an operator, and a weight.
A request source statement defines the origin of a name resolution request. You can define the origin of a request as one of the following:
A destination statement defines the resource to which the Link Controller system directs the name resolution request. The types of resources available for a destination statement are as follows:
You can select one of two operators for both a request source and a destination statement. The is operator indicates that the name resolution request matches the statement. The is not operator indicates that the name resolution request does not match the statement.
The last element of a topology record, called the topology score or weight, allows the Link Controller system to evaluate the best resolution option for a DNS request. In the event that a name resolution request matches more than one topology record, the Link Controller system uses the record with the highest weight attribute to determine which statement it uses to load balance the request.
1.
On the Main tab of the navigation pane, expand Link Controller and then click Topology.
The main screen for topologies opens.
2.
Click the Create button.
The New Record screen opens.
a)
b)
c)
Define the criteria for the request source statement. For example, if the statement focuses on an IP subnet, a box appears that allows you to define that subnet.
b)
c)
Define the criteria for the destination statement. For example, if the statement focuses on an IP subnet, a box appears that allows you to define that subnet.
5.
In the Weight box, specify the priority this record has over topology records.
6.
Click the Create button to save the new topology.
As your network changes, you might find that you need to refine your existing topology records, or remove outdated topology records.
For example, the fictional company SiteRequest has an existing topology statement that routes all traffic originating from the United States to the New York data center. Last week, a new data center in Los Angeles came online. One of the results of this new data center is that the topology record that the Link Controller system used to direct traffic was obsolete, and needed to be removed.
1.
On the Main tab of the navigation pane, expand Link Controller and then click Topology.
The main screen for topologies opens.
2.
Select the topology record that you want to remove from the topology records list by checking the corresponding Select check box.
3.
Click the Delete button.
You can use the Topology load balancing mode to distribute traffic among the pools in a wide IP. To do this, you must have at least two pools configured in the wide IP. With topology load balancing, you send name resolution requests to specific resources based on the origin of the request.
1.
On the Main tab of the navigation pane, expand Link Controller and then click Inbound Wide IPs.
The Wide IPs screen opens.
2.
Click the name of the wide IP for which you want to assign topology-based load balancing.
The properties screen for the wide IP opens.
3.
On the menu bar, click Members.
The Members screen opens. This screen contains a list of the pools currently assigned to the wide IP.
4.
In the Load Balancing Method section, select Topology as the preferred, alternate, or fallback method.
5.
Click the Update button to save your changes.
To further refine the topology load balancing capabilities of the Link Controller system, you can create custom topology regions. A region is a customized collection of topologies. For example, you could create a topology for Denmark, Iceland, Finland, Norway, and Sweden. These topologies could than compose a custom region for Scandinavia. Regions allow you to extend the functionality of your topologies by allowing you to define specific geographical regions that have meaning for your network.
You create a custom region by adding one or more region member types to the region member list. The available region member types are as follows:
Once you select a region member type, you then fill in the details about that region member and add it to the region member list. The region member options change based on the region member type that you select. When you have finished adding region members to your new region, the new region becomes an option in the Create Topology screen.
1.
On the Main tab of the navigation pane, expand Link Controller and then click Topology.
The main topology screen opens.
2.
On the menu bar, click Regions.
The main region screen opens.
3.
Click the Create button.
The Create Region screen opens.
4.
In the Name box, type a name for the new region.
5.
Using the Member List settings, define the appropriate region members.
6.
Click the Create button to create the new region.
The Link Controller system supports the Longest Match option that affects how the system load balances name resolution requests.
The Longest Match option instructs the Link Controller system to use the topology statement that most completely matches the source IP address of the name resolution request. For example, two topology statements exist: one that matches a source IP address of 10.0.0.0 and one that matches 10.15.0.0. A name resolution request arrives with a source IP address of 10.15.65.8. With the Longest Match setting enabled, the Link Controller system uses the topology statement with 10.15.0.0 because it has the longest, and therefore most complete, match. If this option is disabled, the system uses either topology statement, depending on factors such as the weight of the statement or the order in which the statements are listed. This option is enabled by default.
1.
On the Main tab of the navigation pane, expand System and then click Configuration.
The general properties screen opens.
2.
From the Global Traffic menu, choose Load Balancing.
The load balancing properties screen opens.
3.
4.
Click the Update button to save your changes.
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