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Description: In this video we will do an in-depth study of the hierarchical nature of a DNS lookup resolution. For the uninitiated, DNS servers are arranged in a hierarchy as shown in the diagram below - the responsibility of every server level, is to either resolve the request itself and reply, or to reply telling which is the next server that can affirmatively answer the original query. To demonstrate this we use the DIG (Domain Information Groper) utility and will query the DNS servers directly. In this example, lets say we want to find the IP address of mail.google.com, the steps we shall follow are:

1. Use Dig to list all the Root DNS servers configured on the current host

2. Send a DNS request to one of these Root servers for info about mail.google.com

3. The Root server will point us to a list of Top Level Domain (TLD) servers for the .com domain

4. Now we query the authoritative server for the .com domain, which points us to the name servers for the domain google.com

5. We now send the same request to google.com's name server - this time on the server tells us that mail.google.com is actually same as googlemail.1.google.com (CNAME or Canonical Name), so please query for it, instead of mail.google.com, also we have a new list of domain servers to query

6. We now query googlemail.1.google.com to a.googlemail.1.google.com, which finally replies back with the right IP address

The idea behind doing this demo, is to allow the user to understand the DNS queiry and process at the very raw level. I would encourage users to try this our on their own.

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