TTL stands for "Time to Live" in the context of Domain Name System (DNS). It is a value in a DNS resource record that specifies the amount of time the record should be considered valid or cached by a resolver or a caching server. The TTL is measured in seconds.
When a DNS resolver queries a DNS server for a particular domain name, the server includes the TTL value in the response. The resolver then caches the DNS record along with the associated TTL value. The TTL serves as a countdown timer, and once the specified time elapses, the resolver discards the cached record and must query the DNS server again for the most up-to-date information.
Here's a simple example of how TTL works:
A DNS resolver queries a DNS server for the IP address of "www.whoisfreaks.com."
The DNS server responds with the IP address and includes a TTL value, let's say 3600 seconds (1 hour).
The resolver caches the IP address and the TTL value.
For the next hour, if any other device or application requests the IP address for "www.whoisfreaks.com," the resolver will use the cached information.
After one hour (3600 seconds), the TTL expires, and the resolver discards the cached record.
If there's a subsequent request for "www.whoisfreaks.com" after the TTL has expired, the resolver must query the DNS server again to get the latest IP address and TTL.
TTL is crucial for DNS because it helps in managing the caching of DNS records and ensures that outdated information is not used for an extended period. It also helps distribute the load on DNS servers by controlling how frequently clients need to refresh their cached records. DNS administrators set TTL values based on factors such as how often the associated data changes and the desired balance between accuracy and server load.