CompTIA Network+ Practice Test

For DNS, how is TTL measured?

1. In packets

2. In hops

3. By seconds

4. In milliseconds

The correct answer is: By seconds

Time to Live (TTL) in the context of the Domain Name System (DNS) is a value that specifies the duration for which a specific DNS record is considered valid and should be cached by DNS resolvers. This duration is measured in seconds, providing a clear and straightforward metric for how long the information can be stored before it must be refreshed or queried again. When a DNS resolver obtains a record, it keeps that information for the time specified by the TTL. Once this time elapses, the resolver will discard the record and make a new query to the authoritative DNS server to retrieve the most up-to-date information. This is crucial for maintaining accurate and timely DNS records, ensuring that users receive the correct IP address for a given domain name. While some other metrics like packets or hops might be relevant in different networking contexts, they do not apply to how TTL is measured in DNS. Milliseconds, while they measure time, are typically not used for TTL settings in DNS, which standardizes on seconds for ease of understanding and usage across various systems and applications.