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Manual Chapter: Configuration Guide for the BIG-IP® Link Controller: 4 - Working with Listeners
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4

Working with Listeners


Introducing listeners

Before you can fully configure the Link Controller 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 Link Controller and how the system responds to this traffic. In general, you have two options when handling traffic with the Link Controller:

  • The Link Controller 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 Link Controller 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 Link Controller 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 Link Controller, 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 Link Controller.

You control how the Link Controller responds to network traffic on a per-listener basis. For example, a single Link Controller 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 Link Controller, the system always manages and responds to requests for any wide IPs that you have configured on it.

Creating a listener for local resolution

Often, when you add a Link Controller, 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 Link Controller, but you are not limited to wide IPs alone. You can also configure the Link Controller to respond to DNS requests for other network resources that might not be associated with a wide IP.

When a Link Controller 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 Link Controller that corresponds to an IP address that is specifically associated with the system. If the Link Controller is operating as a standalone unit, this IP address is the self IP address you assign to the Link Controller. If the Link Controller is part of a redundant system for high availability purposes, this IP address is the floating IP address that belongs to both systems.

To configure a listener for local resolution

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the Create button.
    The New Listener screen opens.
  3. In the Destination box, type the IP address on which the Link Controller 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 Link Controller 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.

Configuring listeners for traffic forwarding

Another common configuration you can use with the Link Controller is to integrate it with your existing DNS servers. In this scenario, the Link Controller 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 Link Controller is considered to be operating in bridge or router mode, depending on how the traffic was initially sent to the Link Controller. In this configuration, you assign a listener to the Link Controller 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.

To configure a listener for traffic forwarding

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the Create button.
    The New Listener screen opens.
  3. In the Destination box, type the IP address on which the Link Controller listens for network traffic.
    In this case, the IP address that you add is the IP address of the DNS server that you want to handle the DNS request.
  4. From the VLAN Traffic list, select a VLAN setting appropriate for this listener.
    Typically, if the Link Controller 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.

Configuring a wildcard listener

In some cases, you might want the Link Controller to handle any traffic coming into your network, regardless of the destination IP address of the given DNS request. In this configuration, the Link Controller 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 Link Controller. A wildcard listener is the same as a standard listener, except that it contains an asterisk (*) instead of an IP address.

To configure a wildcard listener

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the Create button.
    The New Listener screen opens.
  3. In the Destination box, type an asterisk (*).
  4. From the VLAN Traffic list, select a VLAN setting appropriate for this listener.
  5. Click the Finished button to save the new listener.

Modifying listeners

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.

To modify a listener

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the name of the listener.
    The properties screen for that listener appears.
  3. Modify the settings for the listener.
  4. Click the Update button to save your changes to the listener.

Deleting listeners

In the event that a listener is no longer needed within the Link Controller, you can delete it.

To delete a listener

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Check the Select box that corresponds to the listener entry.
  3. Click the Delete button.
    A confirmation screen appears.
  4. Click the Delete button to delete the listener.

Using listeners with VLANs

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 Link Controller, 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.

Setting up a listener for all VLANs

If the Link Controller 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 Link Controller is responsible, you set the VLAN Traffic option to All VLANs.

To set up a listener for all available VLANs

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the Create button.
    The New Listener screen opens.
  3. In the Destination box, type the IP address on which the Link Controller will listen for network traffic.
  4. From the VLAN Traffic list, select All VLANs.
  5. Click the Finished button to save your changes.

Enabling a listener for specific VLANs

If the Link Controller manages traffic for only some of the VLANs available on the network segment, you set the VLAN Traffic option to Enabled on.

To set up a listener for all available VLANs

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the Create button.
    The New Listener screen opens.
  3. In the Destination box, type the IP address on which the Link Controller will listen for network traffic.
  4. From the VLAN Traffic list, select Enabled on.
    A new option, VLAN List, appears on the screen.
  5. Select the appropriate VLANs from the Available list and use the buttons provided to move them to the Selected list.
    The listener only alerts the Link Controller about traffic on the VLANs in the Selected list.
  6. Click the Finished button to save your changes.

Disabling a listener for specific VLANs

In instances where the Link Controller 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.

To set up a listener for all available VLANs

  1. On the Main tab of the navigation pane, expand Link Controller and then click Listeners.
    The main listeners screen opens.
  2. Click the Create button.
    The New Listener screen opens.
  3. From the VLAN Traffic list, select Disabled on.
    A new option, VLAN List, appears on the screen.
  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 Link Controller about traffic on all VLANs except those listed in the Selected list.
  5. Click the Finished button to save your changes.

Understanding listeners: an example

To further illustrate how you configure listeners to control how the Link Controller responds to DNS traffic, consider the fictional company SiteRequest. At this company, a Link Controller is being integrated into a network with the following characteristics:

  • An existing DNS server already exists at IP address 10.2.5.37.
  • There are two VLANs, called external and guests.
  • Two wide IPs will be created: www.siterequest.com and downloads.siterequest.com.

Once integrated into the network, the Link Controller will be responsible for the following:

  • Managing and responding to requests for the wide IPs
  • Forwarding other DNS traffic to the existing DNS server
  • Forwarding any traffic from the guests VLAN to the rest of the network

To implement this configuration, the Link Controller requires three listeners:

  • A listener with an IP address that equals the self IP of the Link Controller. 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 Link Controller to forward traffic sent from the guests VLAN to the rest of the network.

As you can see from this example, the role the Link Controller plays in managing DNS traffic varies depending on the listener through which the traffic arrives. This results in the Link Controller becoming a flexible system for managing DNS traffic in a variety of ways.




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