DNS Is the Internet Phone Book
The Domain Name System (DNS) translates the human-friendly names we type into the numeric addresses machines use to talk to each other. When you visit a site, your computer asks a chain of DNS servers to resolve the name into an address, then connects.
Each domain holds a set of records, and each record type answers a different question: where is the website, where does email go, who is allowed to issue certificates, and so on. Understanding the common record types is essential for anyone configuring a domain, migrating a host, or debugging why a site or email is not working.
You can look up a domain's records with the DNS lookup tool. Note that this is a server-assisted tool: the query is performed by a server on your behalf and the live results returned to you, rather than running inside your browser.
It helps to picture resolution as a chain of questions. Your computer first asks a recursive resolver, which asks the root servers, then the servers for the top-level domain such as .com, and finally the authoritative servers for the specific domain, caching each answer along the way. Knowing this chain makes it far easier to reason about where a lookup is failing and why some changes appear instantly while others lag.
Address and Alias Records: A, AAAA, CNAME
The records that point names at servers are the ones you touch most often.
A record maps a hostname to an IPv4 address, like 203.0.113.10. This is the workhorse that points your domain at a web server.
AAAA record (pronounced "quad-A") does the same job for an IPv6 address. Modern hosts publish both an A and an AAAA record so clients can use either protocol.
CNAME record is an alias: it points one name at another name rather than at an address. For example, www.example.com might be a CNAME to example.com, so both resolve to the same place and you only maintain one A record. A key rule is that a CNAME cannot coexist with other records on the same name, which is why you cannot put a CNAME on a root domain that also needs MX records.
When you change where a name points, the DNS propagation checker queries resolvers in multiple locations so you can see how the update is rolling out.
Mail and Text Records: MX, TXT
Two record types do the heavy lifting for email and verification.
MX record (mail exchanger) tells the world which servers accept email for your domain. Each MX entry has a priority number, and sending servers try the lowest number first, falling back to higher numbers if it is unavailable. Getting MX records right is the difference between receiving mail and silently losing it — you can inspect them with the MX lookup tool.
TXT record holds arbitrary text and has become the home for machine-readable policies. SPF, DKIM, and DMARC email-authentication settings all live in TXT records, as do the verification strings that services ask you to add to prove you own a domain. Because a domain can have many TXT records, reading them carefully matters when debugging deliverability.
Infrastructure Records and the TTL Myth
Three more record types describe the domain's own administration.
NS record (name server) lists the authoritative servers responsible for the domain — the servers that hold the real answers. Check them with the NS lookup tool when a domain is not resolving, as misdelegated name servers are a common cause.
SOA record (start of authority) is the master record for a zone. It names the primary name server and the administrator's email, and carries serial and timing numbers that secondary servers use to stay in sync.
CAA record (certification authority authorization) names which certificate authorities are permitted to issue certificates for your domain, adding a guardrail against mis-issuance.
Finally, the TTL (time to live) on each record is the number of seconds resolvers are allowed to cache the answer. This is the heart of the "propagation" myth: DNS changes do not slowly ripple across the globe like a wave. The new value is available immediately at the authoritative servers — what you are really waiting for is old, cached answers to expire according to their TTL. Lowering a record's TTL a day before a planned change shortens that wait.
Frequently Asked Questions
What is the difference between an A record and a CNAME?
An A record points a hostname directly at an IPv4 address, while a CNAME points one name at another name. A CNAME cannot share a name with other record types, so it is not allowed on a root domain that needs MX records.
Do these DNS lookups run in my browser?
No. The DNS, MX, and NS lookup tools are server-assisted: a server performs the actual query and returns the results to you. They do not resolve records directly inside your browser.
What does TTL control?
TTL (time to live) is how many seconds resolvers may cache a record before asking again. A lower TTL means changes are picked up sooner, at the cost of more frequent lookups against the authoritative servers.
Why does DNS propagation take time?
It is really cache expiry, not propagation. Authoritative servers serve the new value immediately; the delay is old answers lingering in resolver caches until their TTL runs out. Lowering TTL beforehand reduces the wait.