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Manual Chapter: Sending Traffic Through BIG-IP GTM
Manual Chapter
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Overview: Configuring GTM to screen traffic to an existing DNS server

You can use BIG-IP Global Traffic Manager (GTM) as a traffic screener in front of an existing DNS server. With this setup, all DNS traffic flows through BIG-IP GTM. Listeners that you configure on BIG-IP GTM verify incoming DNS queries. If the query is for a wide IP, BIG-IP GTM resolves the request. If the query is for a destination that does not match a wide IP or for an IP address that is not configured on BIG-IP GTM, the system forwards the query to the specified DNS server for resolution. When forwarding a query, BIG-IP GTM transforms the source address to a self IP address on BIG-IP GTM.

Traffic flow when BIG-IP GTM screens traffic to a DNS server

About listeners

A listener is a specialized virtual server that uses port 53 and to which you assign a specific IP address. When traffic is sent to that IP address, the listener alerts BIG-IP GTM and the system either handles the traffic locally or forwards the traffic to the appropriate resource.

You control how BIG-IP GTM responds to network traffic on a per-listener basis. The number of listeners you create depends on your network configuration and the destinations to which you want to send specific DNS requests. For example, a single BIG-IP GTM can be the primary authoritative server for one domain, while forwarding other DNS requests to a different DNS server. Regardless of how many listeners you configure, BIG-IP GTM always manages and responds to requests for the wide IPs that you have configured on the system.

About wildcard listeners

A wildcard listener is a special listener that is assigned an IP address of 0.0.0.0 and the DNS query port (port 53). When you want BIG-IP GTM to handle all DNS traffic coming into your network, regardless of the destination IP address of the given DNS request, you create a wildcard listener. BIG-IP GTM responds not only to wide IP requests, but also forwards other DNS requests to other DNS servers.

Task summary

Perform these tasks to send traffic through BIG-IP GTM.

Placing GTM on your network to forward traffic

You need to determine to which DNS server you want this BIG-IP GTM system to forward traffic.
To forward traffic, you need to place BIG-IP GTM on your network between the existing DNS server and the clients.
  1. Physically connect BIG-IP GTM to your Internet connection.
  2. Connect the DNS server to an Ethernet port on BIG-IP GTM (optional).
  3. Connect the DNS server to a switch.

Creating a listener to forward traffic to a DNS server

Determine to which DNS server you want this listener to forward traffic.

Create a listener that alerts the BIG-IP system to traffic destined for a DNS server.

  1. On the Main tab, click Global Traffic > Listeners. The Listeners List screen opens.
  2. Click Create. The new Listeners screen opens.
  3. In the Destination field, type the IP address on which BIG-IP GTM listens for network traffic. The destination is the IP address of a DNS server to which you want the listener to route traffic.
    Important: The destination must not match a self IP address on BIG-IP GTM.
  4. From the VLAN Traffic list, select All VLANs.
  5. Click Finished.

Creating a wide IP

Ensure that at least one load balancing pool exists in the configuration before you start creating a wide IP.
Create a wide IP to map a FQDN to one or more pools of virtual servers that host the content of the domain.
  1. On the Main tab, click Global Traffic > Wide IPs The Wide IPs List screen opens.
  2. Click Create. The New Wide IP screen opens.
  3. Type a name for the wide IP.
    Tip: You can use two different wildcard characters in the wide IP name: asterisk (*) to represent several characters and question mark (?) to represent a single character. This reduces the number of aliases you have to add to the configuration.
  4. Specify the pools for this wide IP to use for load balancing. The system evaluates the pools in the order in which they are listed, until it finds a matching pool.
    1. From the Poollist, select a pool. A pool can belong to more than one wide IP.
    2. Click Add.
  5. Click Finished.

Implementation results

You now have an implementation in which BIG-IP GTM receives all DNS queries. If the query is for a wide IP, BIG-IP GTM load balances the request to the appropriate resource. If the query is for an IP address of a DNS server, BIG-IP GTM either routes or forwards the query to the DNS server for resolution.

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