- DNS Load Balancer
To use the F5 DNS Load Balancer Cloud Service to provide global DNS traffic management, you need to delegate authority for specific hostnames from your primary DNS server to DNS Load Balancer.
This article outlines how to provide DNS Load Balancing for the hostname, www.example.com, with the DNS Load Balancer.
Primary DNS subdomain delegation
Complete the following steps to configure your primary DNS server to delegate a subdomain to the DNS Load Balancer Cloud Service.
Create a new DNS subdomain within your parent zone for which the F5 DNS Load Balancer Cloud Service is authoritative.
In most cases, it makes sense to create a new subdomain that is used only for this purpose. For example, the subdomain name gslb or dnslb is commonly used.
- Delegate authority for the entire subdomain to DNS Load Balancer.
On the primary DNS server, delegate authority for the subdomain to DNS Load Balancer by modifying the parent zone to include nameserver (NS) records for the new zone and address (A) records for the new nameservers referenced in the NS records.
For example, to delegate authority for the gslb.example.com subdomain to the DNS Load Balancer name servers ns1.f5cloudservices.com and ns2.f5cloudservices.com, the parent zone example.com should contain the following DNS Records:
gslb IN NS ns1.f5cloudservices.com. gslb IN NS ns2.f5cloudservices.com.
Note: The delegation (NS) and glue records are the two bottom resource records:
- On the primary DNS server, create a CNAME record in the parent zone for the hostname to be load balanced. The CNAME record must reference a hostname within the subdomain gslb.example.com you delegated in step 2.
For example, to have the DNS Load Balancer load balance traffic for the www.example.com hostname, the example.com zone should contain the following entry:
www.example.com. IN CNAME www.gslb.example.com
- On the DNS Load Balancer, create a Load Balancer Record (LBR) using the CNAME you just created. Continuing with the previous example, the LBR you create would be www.gslb.example.com.
How DNS Resolution works with DNS Load Balancer
DNS Load Balancer monitors application availability through widely deployed points of presence to determine the health of your load-balanced applications. Depending on the health of your IP endpoints, DNS Load Balancer will direct traffic depending on proximity rules and the health of your application endpoints.
- A client requests DNS resolution for the hostname, www.example.com, via their local DNS resolver.
- The DNS resolver requests the IP address from the authoritative name servers for example.com (in this case, your Primary DNS server).
- The name responds with a CNAME record for www.gslb.example.com that points to DNS Load Balancer.
- The client then requests resolution for the hostname, www.gslb.example.com, from DNS Load Balancer. provides the optimal application endpoint based on proximity rules and application endpoint health.
- DNS Load Balancer replies with an IP addresses pointing to the optimal application endpoint based on proximity rules and application endpoint health.
- The local DNS resolver sends the correct IP address to the client.
- The user is connected to the requested application for www.example.com.
- DNS Load Balancer overview
- Work with DNS Load Balancer