what is the meaning of the 3DNS?

3DNS was the original product name for Global Traffic Manager (GTM).

@kevin Stewart- why there is number three in the 3DNS name? Sorry for silly question..

did any one answer this question why there is 3 before DNS ?

The 3DNS Controller is a F5 Networks product intended to perform wide-area load balacing and high availability of Internet applications and services. It is able to manage traffic for large sites across multiple data centers, and ensure that users are connected to the data center nearest them.

F5 3DNS product is GTM

See this: https://devcentral.f5.com/questions/how-3dns-works