DNS and domain resolution

Why do we need DNS?

We previously learned that IPv4 uses 32-bit addresses commonly written in decimal, while IPv6 uses 128-bit addresses written in hexadecimal. Remembering a numeric address every time we visit a website would be inconvenient.

The original article uses NAVER as an example, citing 223.130.195.200 as an IPv4 address at the time. Instead of remembering that number, a user can enter www.naver.com.

DNS stands for Domain Name System. It provides a way to look up information associated with names, including a host's IP addresses. The process of turning a domain name into an address is called domain resolution. DNS also supports reverse lookups where the relevant records exist.

The numeric address above is a historical example from 2022, not a claim about NAVER's current DNS records.

Following a lookup

The original lesson describes a common home-network path:

1. The computer checks local information, such as its hosts file.
2. If the name is not found locally, it sends a query to the configured resolver, which may be reached through the router.
3. A router or upstream resolver may already have a cached answer from an earlier lookup.
4. An ISP resolver often has many cached answers because it serves many users. An answer can remain cached until its TTL expires.
5. If no cached answer is available, the resolver queries other DNS servers to resolve the name.

TTL, or time to live, limits how long a cached record may be reused before it must be refreshed.

Editorial clarification: the exact path depends on system and DNS configuration; it does not always pass through a caching router or ISP resolver. A recursive resolver normally follows the DNS hierarchy through root, top-level-domain, and authoritative servers rather than simply searching an arbitrary chain of caches.

The original suggests comparing a frequently visited site, such as YouTube, with a site you have never visited to think about caching. Visible page-load time alone, however, is not a reliable DNS measurement: many other factors affect it.