Common DNS Misconceptions

Despite being a foundational internet technology, DNS is often misunderstood—even by technically inclined users. These misconceptions can lead to misconfigurations, poor performance, and unexpected downtime. Below are some of the most common misunderstandings and clarifications.

“DNS is Instantaneous”

Reality: While DNS lookups often feel instantaneous due to caching, changes to DNS records (e.g., A, CNAME, NS) are not always immediately reflected across the internet.

Propagation delay is governed by:

• TTL values on records

• Intermediate caching layers (browsers, OS, resolvers)

• Whether authoritative nameservers push changes in real-time

Using a low TTL helps speed up propagation, but cannot override caches that already exist.

“Changing DNS Records Moves Traffic Instantly”

Reality: DNS is not a real-time traffic switch like BGP or a load balancer. Updates to records only affect new DNS resolutions. Existing clients with cached entries will continue to use the old record until TTL expires.

To transition traffic quickly, coordinated TTL management and pre-warming strategies are required.

“CNAMEs Can Be Used Anywhere”

Reality: CNAME records cannot coexist with any other record for the same name, including common ones like A or MX. Moreover, CNAMEs are not allowed at the zone apex (e.g., example.com) in many DNS providers, unless they support ALIAS or ANAME as workarounds.

“DNS Is Secure by Default”

Reality: DNS is a plaintext protocol and offers no confidentiality or integrity guarantees by default. Without DNSSEC or DNS-over-HTTPS (DoH), queries can be spoofed, intercepted, or modified.

Relying solely on DNS for authentication or trust signals is unsafe unless proper validation layers are added.

“TTL Is Just a Performance Tuning Option”

Reality: TTL directly impacts operational control. A poorly chosen TTL can:

• Prolong the effect of misconfigurations

• Prevent rollback during outages

• Delay the adoption of emergency records (e.g., for failover)

TTL is a strategic setting and should be treated as part of infrastructure design, not just optimization.