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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 query 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 queries to other DNS servers.
  1. On the Main tab, click DNS > Delivery > Load Balancing > Pools or 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 listeners that alert GTM to DNS queries for a pool of DNS servers

Ensure that a pool of DNS servers exists on GTM.
Configure a listener that alerts GTM to DNS queries destined for a pool of DNS servers. The best practice is to create four listeners: one with an IPv4 address that handles UDP traffic, and one with the same IPv4 address that handles TCP traffic; one with an IPv6 address that handles UDP traffic, and one with the same IPv6 address that handles TCP traffic.
Tip: If you have multiple GTM systems in a device group, perform this procedure on only one system.
  1. On the Main tab, click DNS > Delivery > Listeners. The Listeners List screen opens.
  2. Click Create. The Listeners properties screen opens.
  3. In the Name field, type a unique name for the listener.
  4. For the Destination setting, in the Address field, type an IPv4 address on which GTM listens for network traffic.
  5. From the Listener list, select Advanced.
  6. For the Address Translation setting, select the Enabled check box.
  7. In the Service area, from the Protocol list, select UDP.
  8. From the Default Pool list, select the pool to which this listener forwards DNS queries.
  9. Click Finished.
Create another listener with the same IPv4 address and configuration, but select TCP from the Protocol list. Then, create two more listeners, configuring both with the same IPv6 address, but one with the UDP protocol and one with the TCP protocol.

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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