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Manual Chapter: Working with Listeners
Manual Chapter
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Before you can fully configure the Global Traffic Manager to handle name resolution requests, you must determine how the system integrates within your existing network. Part of this integration includes identifying what network traffic is relevant to the Global Traffic Manager and how the system responds to this traffic. In general, you have two options when handling traffic with the Global Traffic Manager:
The Global Traffic Manager receives the traffic, processes it locally, and sends the appropriate DNS response back to the querying server. Global Traffic Managers with this configuration are considered to be running in node mode.
The Global Traffic Manager receives the traffic and forwards it; either to another part of the network or another DNS server. Global Traffic Managers with this configuration are considered to be running in either bridge mode or router mode, depending on where the system is forwarding network traffic.
To control how the Global Traffic Manager handles network traffic, you configure one or more listeners. A listener is a specialized resource that is assigned a specific IP address and uses port 53, the DNS query port. When traffic is sent to that IP address, the listener alerts the Global Traffic Manager, allowing it to handle the traffic locally or forward the traffic to the appropriate resource.
Tip: If you are familiar with the 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 the Global Traffic Manager.

Also, if you configure user accounts using the Local Traffic Manager, you will find that you can assign listeners, like other virtual servers, to specific partitions. We do not recommend this practice, as listeners play an important role in global traffic management. Consequently, we recommend that you assign all listeners to the Common partition.
You control how the 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 for the Global Traffic Manager, the system always manages and responds to requests for any wide IPs that you have configured on it.
Often, when you add a Global Traffic Manager, you want the system to be responsible for responding to at least a subset of your incoming DNS requests. These requests can be directed at wide IPs that you have configured on the Global Traffic Manager, but you are not limited to wide IPs alone. You can also configure the Global Traffic Manager to respond to DNS requests for other network resources that might not be associated with a wide IP.
When a Global Traffic Manager is responsible for managing and responding to DNS traffic locally, it is said to be operating in node mode. In this situation, you assign a listener to the Global Traffic Manager that corresponds to an IP address that is specifically associated with the system. If the Global Traffic Manager is operating as a standalone unit, this IP address is the self IP address you assign to the Global Traffic Manager. If the Global Traffic Manager is part of a redundant system for high availability purposes, this IP address is the floating IP address that belongs to both systems.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the Create button.
3.
In the Destination box, type the IP address on which the Global Traffic Manager listens for network traffic.
In this case, the IP address that you add is either the self IP address of the system, or, in the case of a redundant pair setup, the floating IP address that corresponds to both systems.
4.
From the VLAN Traffic list, select a VLAN setting appropriate for this listener.
Typically, if the Global Traffic Manager is handling traffic on this IP address locally, you would select All VLANs for this option
5.
Click the Finished button to save the new listener.
Another common configuration you can use with the Global Traffic Manager is to integrate it with your existing DNS servers. In this scenario, the Global Traffic Manager handles any traffic related to the wide IPs you assign to it, while sending other DNS requests to another DNS server on your network. When forwarding traffic in this manner, the Global Traffic Manager is considered to be operating in bridge or router mode, depending on how the traffic was initially sent to the Global Traffic Manager. In this configuration, you assign a listener to the Global Traffic Manager that corresponds to the IP address of the DNS server to which you want to forward to traffic.
Unlike the steps described in the section, Creating a listener for local resolution, you can create more than one listener to forward network traffic. The number of listeners depends on your network configuration and the ultimate destination to which you want to send specific DNS requests.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the Create button.
3.
In the Destination box, type the IP address on which the Global Traffic Manager listens for network traffic.
4.
From the VLAN Traffic list, select a VLAN setting appropriate for this listener.
Typically, if the Global Traffic Manager is handling traffic on this IP address locally, you would select All VLANs for this option
5.
Click the Finished button to save the new listener.
In some cases, you might want the Global Traffic Manager to handle any traffic coming into your network, regardless of the destination IP address of the given DNS request. In this configuration, the Global Traffic Manager continues to process and respond to requests for the wide IPs that you configure, but in addition it is responsible for forwarding any other DNS requests to other network resources, such other DNS servers. To accomplish this type of configuration, you assign a wildcard listener to the Global Traffic Manager. A wildcard listener is the same as a standard listener, except that it contains an asterisk (*) instead of an IP address.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the Create button.
3.
In the Destination box, type 0.0.0.0.
4.
From the VLAN Traffic list, select a VLAN setting appropriate for this listener.
5.
Click the Finished button to save the new listener.
After you create a listener, you can access its settings, changing them as needed. Common instances in which you need to modify a listener include adding an additional VLAN, or modifying the IP address of the listener.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the name of the listener.
The properties screen for that listener appears.
4.
Click the Update button to save your changes to the listener.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
3.
Click the Delete button.
4.
Click the Delete button to delete the listener.
One of the features of a BIG-IP system is that 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 demands.
When you assign listeners to the Global Traffic Manager, you must take into account any VLANs that you have created. 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, enabled only on specific VLANs, or disabled on specific VLANs.
Note: For more information about BIG-IP systems and VLANs, see the BIG-IP® Network and System Management Guide.
If the Global Traffic Manager resides on a network segment that does not use VLANs, or if the IP address you assign as a listener is valid for all VLANs for which the Global Traffic Manager is responsible, you set the VLAN Traffic option to All VLANs.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the Create button.
3.
In the Destination text box, type the IP address on which the Global Traffic Manager will listen for network traffic.
4.
From the VLAN Traffic list, select All VLANs.
5.
Click the Finished button to save your changes.
If the Global Traffic Manager manages traffic for only some of the VLANs available on the network segment, you set the VLAN Traffic option to Enabled on.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the Create button.
3.
In the Destination box, type the IP address on which the Global Traffic Manager will listen for network traffic.
4.
From the VLAN Traffic list, select Enabled on.
5.
Select the appropriate VLANs from the Available list and use the buttons provided to move them to the Selected list.
6.
Click the Finished button to save your changes.
In instances where the Global Traffic Manager resides on a network segment with several VLANs, and you want to exclude some VLANs from listener, you set the VLAN Traffic option to Disabled on.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click the Create button.
3.
From the VLAN Traffic list, select Disabled on.
4.
Select the appropriate VLANs from the Available list and use the buttons provided to move them to the Selected list.
The listener alerts the Global Traffic Manager about traffic on all VLANs except those listed in the Selected list.
5.
Click the Finished button to save your changes.
To further illustrate how you configure listeners to control how the Global Traffic Manager responds to DNS traffic, consider the fictional company SiteRequest. At this company, a Global Traffic Manager is being integrated into a network with the following characteristics:
There are two VLANs, called external and guests.
Two wide IPs will be created: 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 equals the self IP of the 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 the 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 the Global Traffic Manager plays in managing DNS traffic varies depending on the listener through which the traffic arrives. This results in the Global Traffic Manager becoming a flexible system for managing DNS traffic in a variety of ways.
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