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.
Vocabulary
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.
