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Manual Chapter: Replacing a DNS Server with the Global Traffic Manager
Manual Chapter
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The primary purposes of the BIG-IP® Global Traffic Manager are to help you manage incoming wide IP traffic, and load balance that traffic to the appropriate network resources. However, wide IP traffic is only part of the overall DNS traffic that a network must handle. You can also use the Global Traffic Manager as the authoritative nameserver for both wide IPs and all other DNS-related traffic. Typically, this requires that the Global Traffic Manager replace an existing DNS server on the network as shown in Figure 3.1.
Figure 3.1 Example of the flow of traffic when the Global Traffic Manager replaces an existing DNS server
To control how the Global Traffic Manager responds to DNS requests, you must configure a listener. A listener is a specialized resource to which you assign a specific IP address and that 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.
In this implementation, you create a listener that corresponds to the self IP address of the Global Traffic Manager. Since the Global Traffic Manager replaces an existing DNS server, this self IP address must correspond with the IP address that denotes the authoritative nameserver for the appropriate domain.
Note: The tasks in this implementation are based on the assumption that you understand BIND and CNAME records. If you are unfamiliar with these topics, F5 Networks recommends that you review the 5th edition of DNS and BIND, available from OReilly.
This implementation describes the tasks necessary to replace an existing DNS server with the Global Traffic Manager. In this example, the existing DNS server has an IP address of 192.168.5.73, while the Global Traffic Manager has an IP address of 192.168.10.105.
Once again, we use the fictional company SiteRequest. SiteRequest recently purchased a Global Traffic Manager to help load balance traffic across two of its web-based applications: store.siterequest.com and checkout.siterequest.com. These applications are subdomains of www.siterequest.com, which an existing DNS server manages. SiteRequest has decided to replace its existing DNS server with the Global Traffic Manager. Earlier, SiteRequest configured the wide IPs that it needs on the system; the final task is to make the Global Traffic Manager the authoritative nameserver for these domains.
Before you configure the Global Traffic Manager to replace the existing DNS server, you need to configure the DNS server to allow zone file transfers to the Global Traffic Manager. You can enable this authorization through the use of an allow-transfer statement that specifies the IP address of the Global Traffic Manager: 192.168.10.105. Refer to your BIND documentation for more information on how to implement an allow-transfer statement.
Another task you must complete before the Global Traffic Manager becomes the primary DNS server is to create a hint zone. Hint zones designate a subset of the root nameservers list. When the local nameserver starts (or restarts), the nameserver queries the root servers in the hint zone for the most current list of root servers.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click ZoneRunner.
3.
Click Create.
4.
From the View Name list, select external.
The external view is a default view to which you can assign different zones.
5.
In the Zone Name box, type the name you want to use for the zone file.
For this example, type Root.
6.
From the Zone Type list, select Hint.
7.
Click Finished.
The next task you must complete before the Global Traffic Manager becomes the primary DNS server is to acquire the siterequest.com zone files from the existing DNS server. You acquire these zone files through the ZoneRunner utility.
Tip: This task requires that you have added an allow-transfer statement to the existing DNS server that authorizes zone transfers to the Global Traffic Manager.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click ZoneRunner.
3.
Click Create.
4.
From the View Name list, select external.
Note: The external view is a default view to which you can assign different zones.
5.
In the Zone Name box, type the name of the zone file. F5 Networks recommends that you use the following format to name zone files: db.<viewname>.<zonename>.
Note: You must include a trailing dot in the zone name.

For this example, type the following:
db.external.siterequest.com.
6.
From the Zone Type list, select Master.
7.
From the Records Creation Method list, select Transfer from Server.
8.
In the Zone File Name box, type the zone file name.
For this example, type db.external.siterequest.com.
9.
In the Source Server box, type the IP address of the existing DNS server.
For this example, type 192.168.5.73.
10.
Click Finished.
At this point, you have configured the Global Traffic Manager as the primary DNS server for the siterequest.com zone. You must now either change the existing DNS server to become a secondary DNS server to the Global Traffic Manager, or remove it from your network.
Note: If you are unfamiliar with how to change a DNS server from a primary DNS server to a secondary DNS server, refer to the 5th edition of DNS and BIND, available from OReilly.
The final task requires you to set up a listener on the Global Traffic Manager. The Global Traffic Manager employs this listener to identify the DNS traffic for which it is responsible. In this implementation, the listener you create is the same as the self IP address of the Global Traffic Manager: 192.168.5.73.
1.
On the Main tab of the navigation pane, expand Global Traffic and then click Listeners.
2.
Click Create.
3.
In the Destination box, type the IP address on which the Global Traffic Manager listens for network traffic.
For this example, type the IP address 192.168.5.73.
4.
From the VLAN Traffic list, select All VLANs.
5.
Click Finished.
You now have an implementation of the Global Traffic Manager that is also the authoritative nameserver for siterequest.com. This system handles any incoming DNS traffic, whether destined for a wide IP or another node of siterequest.com.
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