Domain Name System Overview

GSLB can be complex; thus, it is worth spending the time to understand how the mysterious Domain Name Server (DNS) system works.

DNS consists of three key components:

· The DNS resolver, i.e., the Client: the resolver is responsible for initiating the queries that ultimately lead to a full resolution of the resource required.

· Nameserver: this is the nameserver that the client initially connects to perform DNS resolution.

· Authoritative Name Servers: Include the Top Level Domain (TLD) nameservers and root nameservers.

A typical DNS transaction is explained below:

· A user types ‘example.com’ into a web browser, and the query travels into the Internet and is received by a DNS recursive resolver.

· The resolver then queries a DNS root nameserver (.).

· The root server then responds to the resolver with the address of a Top-Level Domain (TLD) DNS server (such as .com or .net), which stores the information for its domains. When searching for example.com, our request is pointed toward the .com TLD.

· The resolver then requests the .com TLD.

· The TLD server then responds with the IP address of the domain’s nameserver, example.com.

· Lastly, the recursive resolver sends a query to the domain’s nameserver.

· The IP address, for example.com, is then returned to the resolver from the nameserver.

· The DNS resolver then responds to the web browser with the IP address of the domain requested initially.

· Once the eight steps of the DNS lookup have returned the IP address, for example.com, the browser can request the web page:

· The browser makes an HTTP request to the IP address.

· The server at that IP returns the webpage to be rendered in the browser.

This process can be further complicated:

Caching

Resolving nameservers cache responses can send the same response to many clients. Client-side resolvers and applications may have different caching policies.

Note: For testing, we stop and disable the Windows DNS Client within the services section of your operating system. The DNS names will continue to be resolved; however, it will not cache the results or register the computer’s name. Your system administrator will need to decide if this is the best option for your environment, as it may affect other services.

Time To Live

The resolving name server may ignore the Time To Live (TTL) i.e., the caching time for the response.