What is TTL in DNS, and how does it affect resolution?

• A. TTL determines the maximum file size of DNS responses.
• B. TTL specifies the time a domain must stay registered.
• C. TTL controls how many DNS servers can respond to a query.
• D. TTL tells how long a DNS record can be cached before it must be refreshed.

Answer: (D)

In DNS, TTL stands for Time to Live and it determines how long a DNS record is allowed to be cached by resolvers and end-user devices. While a record is cached, future lookups can be served from that cache instead of querying the authoritative servers again, which makes resolution faster and reduces the load on the DNS system.

When the TTL expires, the cached information is considered stale, so a new query must be made to refresh the data. This ensures that changes to DNS records eventually propagate, but the exact time you see the update depends on the TTL value set for that record. A low TTL means quicker updates but more frequent queries; a high TTL means fewer queries but potentially slower propagation of changes.

TTL does not relate to the size of DNS responses, the duration of domain registrations, or how many DNS servers respond. It specifically governs how long cached responses are considered valid.