DNS: How a Browser Finds Your Website

DNS is the system that turns the name you type into the numeric address of a server. Cloudflare describes it as the phone book of the internet: people use domain names, browsers talk to IP addresses, and DNS does the translation [1]. A domain name is not the same thing as a URL or an IP address. The name is what you register. The URL is a specific page on it. The IP is where the server lives [2].

Who answers the question?

Four roles, in order, when nothing is cached. A recursive resolver takes the browser's question. A root nameserver points at the top-level domain. The TLD server, such as the server for .com, points at the domain's own nameserver. The authoritative nameserver holds the record and returns the IP [1]. The resolver is at the start of that chain. The authoritative server is the last stop, the one that actually has the record [1].

Why does the second visit feel instant?

Caching. Cloudflare says a lookup with nothing cached is about eight steps, and caches skip steps. The browser caches DNS. The operating system caches it next, in the stub resolver. The recursive resolver caches it too. Each cache holds the record for a time to live, the TTL [1]. A short TTL means changes show up sooner and the servers answer more often. A long TTL means a change sits in the old answer.

What should you change before you switch hosts?

The TTL, ahead of time. Google's guide for a move that does not change URLs says to lower the DNS TTL to a few hours, at least a week before the cut, so the old answer expires quickly when you point the name at the new server [3]. After the move, crawl rate often dips and then rises. Shut the old host when traffic there is zero [3]. The name did not change. The address it resolves to did.

What is a domain move, if this is not one?

A different name in the address bar. That is a site move with URL changes, and it needs a redirect from each old URL, not only a DNS edit [4]. Change of Address in Search Console is only for a domain or subdomain move. It is not for a hosting change, a www change, or a path change [5]. If the name stays the same, you are in the DNS article. If the name changes, you are in the redirect article.

What does the visitor see if the new server is wrong?

Whatever that IP returns. A 4xx, other than 429, is ignored and can drop an indexed URL over time. A 5xx slows crawling, and a 5xx that persists can get the URL dropped [6]. Pointing DNS at a server that is up and empty is not a successful move. The name resolved. The page did not.

Who is the registrar in this picture?

The company you pay for the name. Registries delegate registration to registrars. There are hundreds of millions of domain names, and a name has a top-level piece, a second-level piece, and sometimes a third [2]. The registrar is where you unlock a transfer. The DNS host is where the records live. They are often the same company. They do not have to be.

What should you not change on the same day?

The name, the host, and the design. Google says a hosting move is the job where URLs stay put, and combining a domain move with a redesign is how traffic gets lost [3] [5]. Lower the TTL, copy the site, test it, then change the record [3]. Leave the redirects and the new domain for a different week if the name is changing [4].

• Name — what people type.
• IP — what the browser connects to.
• TTL — how long caches keep the old answer.
• Resolver — the server that goes and asks.
• Authoritative server — the one that holds your record.

Where does this show up for a small business?

The week you change hosting. The record is part of the build only because someone has to know who can edit it. Maintenance includes noticing the name is about to expire at the registrar, which is a different bill from the host. Security basics include who else has the login to that DNS host.

Where is the cache you can actually see?

On your own computer, the browser cache is the first place a lookup stops, and the operating system cache is the next [1]. Cloudflare notes that Chrome can show its DNS cache at chrome://net-internals/#dns [1]. Clearing your laptop does not clear the resolver your visitors use. Their copy lasts until the TTL you published runs out.

What should you check before a host change?

Find the TTL on the record that points the name at the server. If it is still a day long, lower it and wait, the way Google describes, at least a week at a few hours [3]. Then confirm the new server answers the real pages before you change the record. DNS will do what the record says. It will not fix an empty site.