Kernaali Tools
References

DNS Record Cheat Sheet

Understand common DNS record types, TTLs and frequent configuration mistakes.

Record types

TypePurposeCommon mistake
AName to IPv4 addressPutting a URL or port in address data
AAAAName to IPv6 addressPublishing an address without working IPv6 connectivity
CNAMEAlias to another DNS nameCombining with other ordinary data at the same owner
MXMail exchanger with preferenceUsing an IP instead of a hostname
TXTText strings, including verification dataInventing a verification token
NSAuthoritative name serversConfusing a registrar setting with zone data
SOAZone authority and timing metadataIgnoring serial updates in manually managed zones
PTRReverse address name to hostnameAssuming an A record creates reverse DNS
SRVService target, port, priority and weightUsing it for clients that do not support SRV
CAACertificate-authority authorizationTreating it as a certificate or ownership proof

Original configuration example

A documentation host named router.lab.invalid could have A data 192.0.2.42 and AAAA data 2001:db8:42::1. Its IPv4 PTR owner would be 42.2.0.192.in-addr.arpa. The .invalid name is intentionally nonresolving; these are teaching values, not deployment records.

TTL and changes

TTL is a cache lifetime in seconds, not a promise that every client refreshes instantly. Lowering a TTL does not evict an older cached answer. Plan ahead and account for negative caching when introducing names.

Names and delegation

A trailing dot represents an absolute DNS name in zone-file notation. Provider interfaces may add the zone name automatically, so inspect their instructions before entering a fully qualified value. Reverse DNS is controlled by the address-space operator and can require a separate request.

Alias caution

A conventional CNAME cannot coexist with other ordinary records at the same owner name. At a zone apex, required SOA and NS data make a normal CNAME unsuitable. Provider-specific alias or flattening products are distinct features.

Technical references

Reviewed 9 September 2026. Found an issue? Send a correction with a reproducible example.