Why does a DNS exist?

Think of a phonebook. You can't possible be expected to memorize every number you intend on calling. Similarly, every server has it's own "number", the IP address. For example 192.133.76.0. But again, we won't really remember this number. Remembering "Twitter.com" is easier.

The DNS is the internet's phonebook.

What exactly is "The DNS"?

DNS stands for Domain name system. And it is a hierarchical infrastructure composed of multiple name servers. There are four types of servers in the hierarchy:

1. DNS Resolver: The resolver is what initiates the query, and forwards the request to other DNS Name servers. Sometimes they can also cache.
2. Root-level name servers: Root name servers maintain name server based on top level domains (TLDs) such as .com .io etc. They return a list of servers that hold the IP addesses of the .io domain for example.
3. TLD name servers: they hold the IP addresses of authoritative servers of the organization.
4. Authoritative name servers: They provide the IP Addresses of the application servers.

Two types of queries:

There are Iterative and Recursive queries to the DNS. Iterative is usually preferred to reduce query load

1. Iterative: The local server requests for the root, TLD, and the authoritative servers for they IP address
2. Recursive: The end user requests the local server. The local server forwards the request to other name servers.

Caching

Caching is used in the browser, the operating systems, the local name server, and on the ISP. They are used to make the user experience faster, and reduce load.![[Screenshot 2023-11-06 at 11.12.20 PM.png]]

Distribution:

The DNS hierarchy ex extremely distributed. There are 13 logical root name server on the world, and they are managed by 12 different organizations.

Scalability

There are about 1000 replications of the 13 servers. Those offer additional capacity, and reduced latency.