What is the TTL value in the Rutgers.edu SOA record?

• A. 60
• B. 2400
• C. 3600
• D. 86400

Answer: (B)

DNS TTL (time-to-live) defines how long resolvers can cache a record before asking the authoritative server again. The value is set per zone, usually via a $TTL directive, and that TTL applies to records in the zone unless an individual record specifies a different TTL. In the Rutgers.edu zone, the default TTL is 2400 seconds, so cached responses from this zone expire after 40 minutes. That’s why the TTL value shown for the Rutgers.edu SOA record is 2400.

Other common TTLs like 60 seconds (very short), 3600 seconds (one hour), or 86400 seconds (one day) are just different caching durations; they aren’t what Rutgers.edu uses for its zone default. Note that the SOA's MINIMUM field historically related to negative caching TTL, while the zone’s overall TTL determines how long most records are cached.