TTL (Time To Live) is a value associated with every DNS record that specifies how long a recursive DNS resolver may cache the record before querying the authoritative DNS server again.
TTL is measured in seconds.
Without caching, every DNS query would require contacting the authoritative DNS server.
Caching reduces:
TTL tells recursive resolvers how long they may use a cached answer.
Suppose the following record exists:
example.com. 3600 IN A 93.184.216.34
Here:
A recursive resolver may cache this record for one hour.
The first user requests:
example.com
The resolver:
Subsequent users receive the cached answer until the TTL expires.
User │ ▼ Recursive Resolver │ (Cache) TTL = 3600 s
When the TTL reaches zero, the resolver performs a new lookup.
| TTL | Meaning | Typical Usage |
|---|---|---|
| 60 | 1 minute | Testing or frequently changing records |
| 300 | 5 minutes | Dynamic services |
| 900 | 15 minutes | Moderate changes |
| 3600 | 1 hour | Common default |
| 86400 | 24 hours | Stable records |
TTL directly affects DNS propagation.
Suppose:
Old Record: 93.184.216.34 TTL: 3600
If you change the IP address immediately after a resolver caches the old record, that resolver may continue serving the old address for up to:
3600 seconds
even though the authoritative server already contains the new record.
When planning a DNS migration:
Example:
Day 1 TTL = 86400 ↓ Lower TTL to 300 ↓ Wait 24 hours ↓ Change IP Address ↓ Most users update within 5 minutes
No.
TTL specifies the maximum recommended cache lifetime.
Some resolvers:
Therefore propagation time is usually close to—but not always exactly equal to—the TTL.
DNS lookup tools display the remaining TTL returned by the queried DNS server.
Example:
example.com A Record: 93.184.216.34 TTL: 287
A remaining TTL of 287 seconds means the resolver will likely continue serving the cached record for another 287 seconds before querying the authoritative server again.
Telenegar DNS Check displays the TTL returned by each DNS server.
Comparing TTL values from multiple resolvers can help identify:
dns ttl cache propagation resolver authoritative