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Manual Chapter: Placing BIG-IP GTM in front of a Pool of DNS Servers
Manual Chapter
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Overview: Screening and forwarding non-wide IP traffic to a pool of DNS servers

BIG-IP Global Traffic Manager (GTM) can function as a traffic screener in front of a pool of DNS servers. In this situation, BIG-IP GTM checks incoming DNS queries and if the query is for a wide IP, resolves the query. Otherwise, BIG-IP GTM forwards the DNS query to one of the servers in a pool of DNS servers, and that server handles the query.

Traffic flow when BIG-IP GTM screens traffic to a pool of DNS servers Traffic flow when BIG-IP GTM screens traffic to a pool of DNS servers

About listeners

A listener is a specialized virtual server that passively checks for DNS packets on port 53 and the IP address you assign to the listener. When a DNS name resolution request is sent to the IP address of the listener, BIG-IP GTM either handles the request locally or forwards the request to the appropriate resource.

Task summary

Perform these tasks to screen non-wide IP traffic and forward the traffic to a pool of DNS servers.

Creating a pool of local DNS servers

Ensure that at least one custom DNS monitor exists on the BIG-IP system. Gather the IP addresses of the DNS servers that you want to include in a pool to which the BIG-IP system load balances DNS traffic.
Create a pool of local DNS servers when you want to load balance DNS requests to back end DNS servers.
  1. On the Main tab, click Local Traffic > Pools. The Pool List screen opens.
  2. Click Create. The New Pool screen opens.
  3. In the Name field, type a unique name for the pool.
  4. For the Health Monitors setting, from the Available list, select the custom DNS monitor you created, and click << to move the monitor to the Active list.
  5. Using the New Members setting, add each resource that you want to include in the pool:
    1. Type an IP address in the Address field.
    2. Type a port number in the Service Port field, or select a service name from the list.
    3. To specify a priority group, type a priority number in the Priority Group Activation field.
    4. Click Add.
  6. Click Finished.

Creating a listener that alerts GTM to DNS queries for a pool of DNS servers

Configure a listener that alerts BIG-IP GTM to DNS queries destined for DNS servers that are members of a pool.
  1. Log on to the command-line interface of BIG-IP GTM.
  2. Type tmsh, to access the Traffic Management Shell.
  3. Run this command sequence to create a listener: create /gtm listener <name of listener> address <IP address on which you want the listener to alert GTM to DNS traffic> ip-protocol udp pool <name of pool> translate-address enabled The system creates a listener with the specified name and IP address that alerts BIG-IP GTM to queries destined for the members of the specified pool.
  4. Run this command sequence to save the listener: save /sys config
  5. Run this command sequence to display the listener: list /gtm listener The system displays the new listener configuration.

Implementation result

You now have an implementation in which BIG-IP GTM receives DNS queries, handles wide IP requests, and forwards all other DNS queries to members of the pool of DNS servers.

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