Subdomain
A domain that is part of a larger domain, like blog.example.com or api.example.com.
A subdomain is a prefix added to your main domain to create a separate web address. In blog.example.com, "blog" is the subdomain and "example.com" is the parent domain. Subdomains can have their own DNS records, pointing to different servers or services. Common uses include api.example.com for APIs, mail.example.com for email, and staging.example.com for testing. Each subdomain needs its own A, AAAA, or CNAME record in DNS. There is no limit to how many subdomains you can create.
Related terms
See also
Referenced on
- Brute-force defense for wp-login.php
- Complete Guide to DNS Attacks and DNS Security (Prevention, Testing & Mitigation)
- Dangling CNAMEs and Subdomain Takeover Risk Across the Global DNS
- DMARC Record Checker, Email Policy Analyzer
- DNS Checker Bot & Scanner Documentation
- DNS Hijacking Explained: How Attackers Take Control of Your Domain's Resolution
- DNS Inspector: Free DNS Lookup & Health Check
- DNS Over HTTPS Abuse: How Encrypted DNS Creates Security Blind Spots
- DNS Rebinding Attack: How Browsers Are Tricked Into Bypassing Same-Origin Policy
- DNS Tunneling Attack: How Data Is Smuggled Through Port 53
- DNS Water Torture Attack: How Random Subdomain Floods Overwhelm Nameservers
- DNS Zone Transfer Attack (AXFR): How a Single Query Exposes Your Entire Domain
- DNS Zone Walking at the TLD Level: NSEC, NSEC3, and Coverage Limits
- DNS Zone Walking for Subdomain Enumeration: How NSEC Exposes Your Subdomains
- Email Authentication by the Numbers: Historical SPF and DMARC TXT Snapshots
- How Expired Name Servers Become Domain Hijacking Vectors
- How to Report Malware and Botnet Command-and-Control Traffic From an IP Address
- How to Report Phishing Emails and Websites Hosted on an IP Address
- How to Set Up a Custom Domain for Your Email (Google Workspace, Microsoft 365)
- How to Verify DNS Changes After Switching Hosting Providers
- HTTP Security Headers Analyzer & Generator
- IPv6 in Historical DNS Data: AAAA Records from 2017 to 2020
- NXDOMAIN Attack: How Nonexistent Domain Floods Exhaust DNS Resolvers
- Phantom Domain Attack: How Unresponsive Domains Exhaust DNS Resolvers
- Redirect Checker, Trace HTTP Redirect Chains
- Reverse IP Lookup: Find All Domains Hosted on an IP Address
- SMTP Diagnostics, Test Mail Server Connectivity
- SPF Record Checker, Validate & Generate SPF
- SPF, DKIM, and DMARC: How DNS Protects Your Email From Spoofing
- Subdomain Takeover: How Dangling DNS Records Let Attackers Hijack Your Domain