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Manual Chapter: Listeners
Manual Chapter
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Before you can fully configure Global Traffic Manager to handle name resolution requests, you must determine how you want the system to integrate with the existing network. Specifically, you must identify what network traffic you want Global Traffic Manager to handle and how. In general, the system performs global traffic management in two ways: Node mode and Bridge or Router mode.
Typically, when you add a Global Traffic Manager system to your network, you want the system to respond to at least a subset of your incoming DNS requests. You can configure the system to direct the requests to the wide IPs that are configured on Global Traffic Manager; however, you can also configure the system to respond to DNS requests for other network resources that are not associated with a wide IP, such as other DNS servers.
When Global Traffic Manager receives traffic, processes it locally, and sends the appropriate Domain Name System (DNS) response back to the querying server, it is operating in Node mode. In this situation, you create a listener that corresponds to an IP address on the system. If Global Traffic Manager operates as a standalone unit, this IP address is the self IP address of the system. If Global Traffic Manager is part of a redundant system configuration for high availability purposes, this IP address is the floating IP address that belongs to both systems.
Another common way to use Global Traffic Manager is to integrate it with the existing DNS servers. In this scenario, Global Traffic Manager handles any traffic related to the wide IPs you assign to it, while forwarding other DNS requests either to another part of the network or another DNS server. When forwarding traffic in this manner, Global Traffic Manager is operating in Bridge or Router mode, depending on how the traffic was initially sent to the system. In this configuration, you assign to Global Traffic Manager a listener that corresponds to the IP address of the DNS server to which you want to forward to traffic.
You can create multiple listeners to forward network traffic. The number of listeners you create is based on your network configuration and the ultimate destination to which you want to send specific DNS requests.
In some cases, you might want Global Traffic Manager to handle the traffic coming into your network, regardless of the destination IP address of the given DNS request. In this configuration, Global Traffic Manager continues to process and respond to requests for the wide IPs that you configure, but is also responsible for forwarding additional DNS requests to other network resources, such as DNS servers. To accomplish this type of configuration, you create a wildcard listener.
To control how Global Traffic Manager handles network traffic, you configure one or more listeners. A listener is a specialized resource to which you assign a specific IP address and port 53, the DNS query port. When traffic is sent to that IP address, the listener alerts Global Traffic Manager, allowing it to either handle the traffic locally or forward the traffic to the appropriate resource.
Tip: If you are familiar with Local Traffic Manager, it might be helpful to consider a listener as a specialized type of virtual server that is responsible for handling traffic for Global Traffic Manager.
Note: If you configure user accounts on Local Traffic Manager, you can assign listeners, like other virtual servers, to specific partitions. However, because listeners play an important role in global traffic management, F5 Networks recommends that you assign all listeners to partition Common.
You control how Global Traffic Manager responds to network traffic on a per-listener basis. For example, a single Global Traffic Manager can be the authoritative server for one domain, while forwarding other requests to a separate DNS server. Regardless of how many listeners you configure, the system manages and responds to requests for the wide IPs that are configured on it.
To further illustrate how you configure listeners to control how Global Traffic Manager responds to DNS traffic, consider the fictional company SiteRequest. At this company, Global Traffic Manager is being integrated into a network with the following characteristics:
There are two VLANs, named external and guests.
There are two wide IPs: www.siterequest.com and downloads.siterequest.com.
Forwarding any traffic from the guests VLAN to the rest of the network
A listener with an IP address that is the same as the self IP address of Global Traffic Manager. This listener allows the system to manage DNS traffic that pertains to its wide IPs.
A listener with an IP address of 10.2.5.37, the IP address of the existing DNS server. This listener allows the system to forward incoming traffic to the existing DNS server.
A wildcard listener enabled on the guests VLAN. This listener allows Global Traffic Manager to forward traffic sent from the guests VLAN to the rest of the network.
As you can see from this example, the role that Global Traffic Manager plays in managing DNS traffic varies depending on the listener through which the traffic arrives. As a result, Global Traffic Manager becomes a flexible system for managing DNS traffic in a variety of ways.
On BIG-IP systems, you can create one or more VLANs and assign specific interfaces to the VLANs of your choice. By default, each BIG-IP system includes at least two VLANs, named internal and external. However, you can create as many VLANs as the needs of your network demand.
When you assign listeners to Global Traffic Manager, you must take into account the VLANs that are configured on the system. For example, a listener that forwards traffic to another DNS server might only be appropriate for a specific VLAN, while a wildcard listener might be applicable to all VLANs. You can configure a listener to be applicable to all VLANs, or enabled only on specific VLANs.
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