tl;dr - BIG-IP DNS provides global load balancing (GSLB), DNS services, and basic DDoS protection features.
By now we all understand the concepts behind load balancing; creating a virtual access point to distribute traffic across multiple resources. Keeping that idea in mind the next question is how do we advertise our application available across separate data centers? BIG-IP DNS (formerly Global Traffic Manager or GTM) first and foremost is a global load balancer for DNS queries. Using similar algorithms for load balancing decision made by BIG-IP Local Traffic Manager (LTM), BIG-IP DNS routes your DNS traffic to the best suited datacenter either on premise, co-located, or in your preferred cloud provider. BIG-IP DNS also provides DNS resolution services, including caching and traffic throttling to ensure queries made about your applications are always answered and fast.
To understand BIG-IP DNS, we'll first define a few product terms.
Wide IP - Owns your services FQDN and responds to listener requests. The Wide IP contains one or more pools which in turn contain one or more virtual servers.
Server - In this case, the server defined in BIG-IP DNS is either a BIG-IP or other 3rd party system responsible for owning one or more virtual server service.
GSLB - Global Server Load Balancing. The GSLB section within BIG-IP DNS configuration is the core of intelligent DNS resolution services.
Listener - BIG-IP uses TCP/UDP listeners to respond to DNS queries.
Pool - In BIG-IP DNS a pool contains one or more virtual servers.
How BIG-IP DNS Works
BIG-IP DNS has grown over the years to incorporate many new features, but we'll stick to discussing the core global server load balancing (GSLB) functionality. Let's first take a look at a traditional DNS query (we're assuming no system has example cached):
Client queries www.example.com to local DNS (LDNS)
LDNS queries ROOT Servers
ROOT Servers send the query to the .com TLD server
TLD Servers provide the name server IP for example.com to LDNS server (glue records if you got em)
example.com name servers lookup www entry and send to LDNS request
LDNS Server returns IP for www.example.com to client
Client is now browsing.
BIG-IP DNS enters the picture at step 5 and adds a few extra steps:
BIG-IP DNS Listener receives the query for example.com
The Wide-IP associated to example.com makes a load balancing decision on what pool to send the request to
The chosen pool makes a secondary load balancing decision on what virtual server to send the request to
The virtual server IP is returned to the originating LDNS server
Client is more happy because they were routed to a regionally located server with faster response times.
In this scenario, the BIG-IP DNS provided a faster application experience for the user by determining the region the user resided and provided the fastest performing server's as the IP for the FQDN requested by DNS.
BIG-IP DNS provides more features to enhance the GSLB features including accelerating DNS resolution and acting as a fast secondary DNS server. Below you can learn more about BIG-IP DNS and as always if you have questions or comment please let us know.