What is TTL and how do I choose a value?

TTL (Time To Live) is the number of seconds a DNS server is allowed to cache a record before checking its current value again. Every DNS record (A, MX, TXT, etc.) has its own TTL, usually expressed in seconds (e.g. 3600 = 1 hour).

How TTL affects a change's propagation:

• A low TTL (e.g. 300 seconds / 5 minutes) — changes become visible everywhere quickly, but DNS servers need to be queried more often, which can slightly increase load;
• A high TTL (e.g. 86400 seconds / 24 hours) — reduces the number of queries, but any later change will take longer to fully propagate, because many servers will keep using the old cached value until it expires.

Practical recommendation: if you know in advance that you're about to make an important change (for example moving your site to another server or changing nameservers), lower the TTL a few days beforehand, to a small value (300-600 seconds). Once the change has propagated and you've confirmed everything works correctly, you can raise the TTL back to a larger value (3600-86400 seconds) for more efficient operation long-term.