What is the function of DNS resilience and TTL?

• A. TTL determines the maximum number of DNS records that can be cached.
• B. DNS resilience refers to data encryption for DNS queries.
• C. TTL sets the expiration date of the DNS zone.
• D. TTL controls how long a DNS record is cached; resilience involves redundant DNS infrastructure to prevent outages.

Answer: (D)

DNS caching duration is governed by TTL. The Time To Live value tells resolvers how long a DNS record should be kept in a cache before the resolver must fetch a fresh copy from an authoritative source. This caching reduces unnecessary queries, lowers latency for repeated lookups, and decreases the load on DNS servers. However, once TTL expires, any change to the record will propagate only after that cache expires, which is why very short TTLs allow faster updates and very long TTLs reduce traffic but slow down change propagation. TTL is applied per record and does not set an expiration date for the entire zone.

DNS resilience is about keeping resolution available even if some parts of the system fail. This means using redundant authoritative servers, geographic distribution, and robust failover and monitoring so that if one server or path goes down, others can still respond.

Together, the intended concept is that TTL controls how long a DNS record is cached, while resilience involves redundant DNS infrastructure to prevent outages.