The Time To Live (TTL) mechanism is used to determine the lifespan of data packets travelling through a computer or across a network. In practice, it represents a counter or a predefined time limit; once this limit is reached or expires, the affected data packet is discarded. This mechanism is necessary in computer networks to prevent data from circulating endlessly within the system.
In the case of DNS records, TTL is used to facilitate communication between servers and is set by an authoritative nameserver. During operation, a caching nameserver stores the requested resource record for the duration specified by the TTL value after a query has been made. As a result, if another request arrives within this period, the caching nameserver does not need to query the authoritative nameserver again.
When configuring DNS records, the TTL value is specified in seconds. For example, a TTL value of 3600 means that the record will be cached for 1 hour. Setting a lower TTL value allows the resource record to refresh more quickly; however, it also increases the load on the authoritative nameserver. To prevent unnecessary strain on the nameserver, it is generally recommended to set the TTL value to 3600 seconds by default.