How TTL works
When a resolver receives an answer from a DNS server, it caches the record for a time equal to its TTL (for example 3600 seconds — one hour). Until the TTL expires, repeat lookups are served from the cache without contacting the authoritative server. This speeds up name resolution and reduces load on the infrastructure.
Which value to choose
A TTL value is a trade-off between how fast changes spread and how much load you generate:
- High TTL (a day) — fewer queries, but changes to an A record or CNAME propagate slowly.
- Low TTL (minutes) — changes apply quickly, which matters before a site migration or for Dynamic DNS.
- Practice — the TTL is temporarily lowered before a planned address change, then raised back.
A well-chosen TTL balances data freshness against caching efficiency.
