Domain Name System (DNS) Part 1

15 Mar 2019

This is the first part Domain Name System (DNS). Click here to see part 2.

Definition

Domain Name System is:

• A distributed database implemented in a hierarchy of DNS servers, and
• An application-layer protocol running over UDP on port 53 that allows hosts to query the distributed database.

~ The Power of Habit

It is specified in [RFC 1034] and [RFC 1035].

How DNS Works

DNS is not just any one DNS server but a network of DNS servers. Let’s look at how the DNS resolves a domain name like salesdepartment.mycompany.com.

1. Host –> Local DNS server
2. Local DNS server –> Root DNS server
   1. Q: Do you know the IP address of salesdepartment.mycompany.com?
   2. A: No I don’t, but this Top Level Domain DNS server is in charge of .com top level domain.
3. Local DNS server –> the .com Top Level Domain DNS server
   1. Q: Do you know the IP address of salesdepartment.mycompany.com?
   2. A: No I don’t, but this Intermediate DNS server is in charge of mycompany.com domain.
4. Local DNS server –> the .mycompany.com intermediate DNS server
   1. Q: Do you know the IP address of salesdepartment.mycompany.com?
   2. A: No I don’t, but this Authoritative DNS server does.
5. Local DNS server –> Authoritative DNS server
   1. Q: Do you know the IP address of salesdepartment.mycompany.com?
   2. A: Yes, it’s at .

Note Local DNS server is genenerally not considered part of the hieararchy of DNS servers.