What Is DNS TTL?
TTL (Time to Live) is a value in DNS records that tells resolvers how long to cache a record before requesting a fresh copy from the authoritative server. It is measured in seconds and directly impacts how quickly DNS changes propagate.
How It Works
When a resolver fetches a DNS record, the TTL tells it how many seconds to keep the record in cache. A TTL of 3600 means the resolver will use the cached value for one hour. After expiration, the resolver queries the authoritative server again. Lower TTL values mean faster updates but more DNS queries.
Why It Matters
TTL affects website availability during migrations, failover speed, and DNS server load. Setting TTL too high means changes propagate slowly. Setting it too low increases query volume and can increase latency. Finding the right balance is key to reliable DNS management.
Common Issues
- High TTL values causing slow propagation during migrations
- Very low TTL values increasing DNS query costs
- ISP resolvers ignoring TTL and caching longer
- Forgetting to lower TTL before planned changes