DNS Records Explained: A, AAAA, CNAME, MX, TXT, NS and More

What Is DNS and How Does Domain Resolution Work?

The Domain Name System (DNS) is often described as the internet's phonebook. Computers, routers, and load balancers do not understand human-friendly addresses like silixen.shop; they communicate through numerical IP addresses such as 76.76.21.21 (IPv4) or hexadecimal strings like 2606:4700::6810:85e5 (IPv6).

When you enter a web address into your browser, an entire distributed hierarchy executes in milliseconds:

1. Recursive Resolver: Your computer or ISP forwards the request to a recursive DNS resolver (such as Cloudflare's 1.1.1.1 or Google's 8.8.8.8). If the answer is cached, it is returned instantly.
2. Root Servers: If uncached, the resolver asks one of the 13 worldwide root server clusters for the location of the Top-Level Domain (TLD) nameservers.
3. TLD Nameservers: The TLD registry (such as Verisign for .com) points the resolver to the authoritative nameservers chosen by the domain registrar.
4. Authoritative Nameservers: The authoritative servers hold the official zone file for the domain and return the exact IP or canonical alias with its associated Time to Live (TTL).

DNS Record Comparison Table

Here is a quick overview of the most critical DNS record types, their technical role, and practical zone file syntax:

Deep Dive: The Core DNS Records

1. A and AAAA Records

The A (Address) record is the foundational block of the web. It binds a domain (or subdomain) directly to a public 32-bit IPv4 address. When you type example.com, an A record provides the exact destination server.

The AAAA (Quad-A) record performs the identical task for IPv6 addresses. Because the global supply of IPv4 addresses is exhausted, modern cloud providers and mobile telecommunications networks prioritize IPv6 routing whenever available.

2. CNAME Records (Canonical Name)

A CNAME record points one domain name to another domain name, rather than an IP address. For instance, you might point www.example.com to example.com or cname.vercel-dns.com.

3. MX Records (Mail Exchange)

Without MX records, your domain cannot receive emails. MX records tell sending mail servers (MTA) where to deliver messages addressed to user@example.com.

MX records include a numerical priority (preference). Lower numbers represent higher priority:

example.com.   IN   MX   1    aspmx.l.google.com. example.com.   IN   MX   5    alt1.aspmx.l.google.com. example.com.   IN   MX   10   alt2.aspmx.l.google.com.

Sending servers attempt to deliver to the priority 1 server first. If Google's primary node is temporarily unreachable, it falls back to priority 5, and then priority 10.

4. TXT Records: Email Security & Verification

Originally intended for arbitrary notes, TXT records have become the backbone of modern internet security, email authentication, and SaaS integration:

• SPF (Sender Policy Framework): Announces which IP addresses and third-party vendors (SendGrid, Mailchimp, Google Workspace) are authorized to send email from your domain:
  v=spf1 include:_spf.google.com include:sendgrid.net ~all
• DKIM (DomainKeys Identified Mail): Publishes a public cryptographic key that receiving servers use to verify that outgoing emails were not altered during transit.
• DMARC (Domain-based Message Authentication): Instructs mail providers whether to quarantine or reject emails that fail SPF or DKIM checks, preventing spoofing and brand impersonation.

5. CAA Records (Certificate Authority Authorization)

A CAA record is an important security mechanism that allows domain owners to declare which Certificate Authorities (CAs) are permitted to issue SSL/TLS certificates for their domain. If an unauthorized CA is compromised or an attacker attempts to generate a fraudulent certificate, the CA must refuse issuance.

What Is TTL and How Does DNS Caching Work?

Every DNS record contains a TTL (Time to Live) value expressed in seconds. The TTL instructs recursive resolvers, ISPs, and client devices how long they are allowed to store the record in their local cache before asking the authoritative nameserver for a fresh copy.

Top 4 DNS Configuration Mistakes to Avoid

• 1. Having Multiple SPF RecordsA domain must publish only one TXT record starting with v=spf1. If you publish two separate SPF records (e.g., one for Google and one for Mailchimp), mail servers treat it as a PermError and reject incoming emails. Merge all vendors into a single record.
• 2. CNAME Record at Apex RootPointing example.com directly to a CNAME breaks MX records and nameserver authority. Use A records or ALIAS/CNAME Flattening provided by Cloudflare, Route 53, or Vercel.
• 3. Forgetting Trailing Dots in BIND / Zone FilesIn traditional DNS zone syntax, omitting a trailing dot from a target domain (e.g. mail.google.com instead of mail.google.com.) appends your origin domain, creating an invalid address like mail.google.com.example.com.
• 4. Not Lowering TTL Prior to Server MigrationsIf you change server IP addresses while your A record has an 86400 TTL, thousands of users will continue reaching your old server for an entire day. Always lower TTL to 300 seconds 48 hours before moving servers.

How to Check and Verify DNS Records with Silixen

To audit your DNS settings or diagnose propagation:

1. Open the free Silixen Domain & DNS Lookup tool.
2. Enter your domain name (such as example.com).
3. Select ALL to view all public records concurrently, or pick a specific type like MX, TXT, or A.
4. Click Check DNS Records. The tool executes an isolated DNS over HTTPS query to Google Public DNS and displays the authoritative response codes, TTL values, and plain-language explanations.