TTL (Time To Live) is the most important factor in DNS propagation speed. Understanding how to manage TTL effectively can mean the difference between a smooth migration and hours of downtime.
What is TTL?
TTL is a value in seconds that tells DNS resolvers how long to cache a record before checking for updates. A TTL of 3600 means the record can be cached for one hour. After that, resolvers must query the authoritative nameserver again. Common TTL values range from 300 (5 minutes) for dynamic records to 86400 (24 hours) for stable records.
Pre-Migration TTL Reduction
The golden rule: lower your TTL before making DNS changes. If your current TTL is 24 hours, change it to 300 seconds (5 minutes) at least 24-48 hours before your planned migration. This ensures all caches have the low TTL by migration time, allowing fast propagation of the actual change.
Post-Migration TTL Increase
After your DNS change has fully propagated and you've verified everything works, increase TTL back to a higher value. Higher TTLs reduce DNS query load on your nameservers and improve resolution speed for users. A TTL of 3600 (1 hour) to 86400 (24 hours) is common for stable records.
TTL Trade-offs
Low TTL means faster propagation but more DNS queries and slightly slower resolution. High TTL means fewer queries and faster resolution but slower propagation. Choose based on how often your records change. Static websites can use 24-hour TTLs; services with frequent failover need 5-minute TTLs.