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Manual Chapter: Topologies
Manual Chapter
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As the name implies, Global Traffic Manager handles name resolution requests at an international level. You can use topologies to load balance these requests. A topology is a set of characteristics that identifies the origin of a given name resolution request. In Global Traffic Manager, topologies belong to one of several categories, including:
A region is a customized collection of topologies. For example, you can create a topology for Denmark, Iceland, Finland, Norway, and Sweden. These topologies can compose a custom region called Scandinavia.
Through topologies, you can instruct Global Traffic Manager to select a data center or 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 also instruct Global Traffic Manager to use topologies to load balance name resolution requests across pools at the wide IP level, and across virtual servers at the pool level.
To better understand topologies, consider the fictional company, SiteRequest, which allows its customers to download applications from its web site. SiteRequest has three data centers: 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.
The New York data center is chosen as the designated data center for any name resolution requests originating in the western hemisphere. To ensure that these requests go only to the New York data center, the IT department first creates a custom region, called Western Hemisphere, that contains the continents North America and South America. With this custom region created, the next step is to create a topology record for Global Traffic Manager. A topology record is a statement that tells Global Traffic Manager 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 pools in the corresponding wide IP,, to use topology load balancing.
Global Traffic Manager uses an IP geolocation database to determine the origin of a name resolution request. The default database provides geolocation data for IPv4 addresses at the continent, country, state, ISP, and organization levels. The state-level data is worldwide, and thus includes designations in other countries that correspond to the U.S. state-level in the geolocation hierarchy, for example, provinces in Canada. The default database also provides geolocation data for IPv6 addresses at the continent and country levels.
Note: You can access the ISP and organization-level geolocation data for IPv4 and IPv6 addresses using the iRules® whereis command.
Tip: If you require geolocation data at the city-level, contact your F5 Networks sales representative to purchase additional database files.
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 a:
A destination statement defines the resource to which Global Traffic Manager 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, specifies the weight of the topology record. The system finds the weight of the first topology record that matches the server object (pool or pool member) and the LDNS. The system then assigns that weight as the topology score for that server object. The system load balances to the server object with the highest topology score. If the system finds no topology record that matches both the server object and the LDNS, then the system assigns that server object a zero score.
You can use the Topology mode to load balance and 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, Global Traffic Manager resolves name resolution requests using the IP addresses of virtual servers in a specific data center or other resource, based on the origin of the request.
In addition to setting up the Topology mode to select a pool within a wide IP, you can also modify the settings to select a virtual server within a pool. However, you must configure the topology records before Global Traffic Manager can use the Topology mode.
To further refine the topology load balancing capabilities of Global Traffic Manager, you can create custom topology regions. 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:
After you select a region member type, you 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.
Global Traffic Manager supports a Longest Match option that affects how the system load balances name resolution requests.
The Longest Match option instructs Global Traffic Manager 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 and one that matches a source IP address of A name resolution request arrives with a source IP address of With the Longest Match setting enabled, Global Traffic Manager uses the topology statement with, because it has the longest, and therefore, most complete, match. If this option is disabled, the order of the topology entries as they exist in /config/gtm/ is preserved. Global Traffic Manager uses the first topology entry found that matches both the LDNS and the server objects. This option is enabled by default.
Note: When you enable the Longest Match option the system gives priority to the topology records that contain IP subnet blocks that you defined using the CIDR format. You can create a region and define an IP subnet using the CIDR format as a member of that region; however, the system gives a higher priority to the IP subnet defined in the topology record.
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