8. Time to Live (TTL)

The TTL is a 32-bit unsigned integer, measured in seconds. It is the time after which the RR must be discarded by a resolver or other caching system. The TTL is set by the authoritative server for the zone, and is used by resolvers to determine how long to cache the RR.

The TTL of an RR is the time after which the RR must be discarded by a resolver or other caching system. The TTL is set by the authoritative server for the zone, and is used by resolvers to determine how long to cache the RR.

The TTL of an RR must be the same as the TTL of all other RRs in the same RRSet. If the TTLs of the RRs in an RRSet are not all the same, the resolver must use the lowest TTL as the TTL of the RRSet (see section 5.2).

The TTL of an RR must not be negative. A TTL of zero means that the RR must not be cached. That is, an RR with a TTL of zero must be discarded by the resolver after it has been used to answer the query that caused it to be fetched.

The TTL of an RR is not a guarantee that the RR will be available for the full TTL. The RR may be discarded before the TTL expires, for example, if the resolver runs out of cache space.

The TTL of an RR is not a guarantee that the RR will be discarded after the TTL expires. The RR may be retained after the TTL expires, for example, if the resolver is unable to refresh the RR (for example, due to a network failure).

The TTL of an RR is not used to determine the validity of the RR. The RR is valid until it is replaced or deleted by the authoritative server for the zone.