Which term defines a counter or duration set on an IP packet or DNS record before it is discarded, representing the maximum router-hops a packet can make?

• A. Time-to-Live (TTL)
• B. Top-Level Domain (TDL)
• C. Token
• D. Tombstone

Answer: (A)

Time to Live is about how long a construct is allowed to exist before it’s discarded. In IP networking, the TTL field acts as a hop counter: each router that forwards the packet decreases this value, and when it hits zero the packet is dropped to prevent endless looping. In DNS, TTL represents how long a resolver can cache a record before it must refresh, effectively setting a time window for the data’s validity. The question’s description of a counter or duration that governs when something is discarded fits this concept exactly.

The other terms don’t match this lifetime idea. A Top-Level Domain is part of a domain name, not a mechanism for limiting lifespan. A Token is a general term without the specific lifetime semantics. Tombstone is used in some systems to mark deletion, not to define how long a packet or DNS record remains usable.