Internet Direct (Indy) Version 9.0.2 Beta
TResultRecord.TTL
Indicates the Time-To-Live for the resource record.

property TTL: cardinal;
Description
TTL is a read-only Cardinal property that indicates the Time-To-Live for the resource record. TTL represents a time limit that is the number of seconds that a resource record is considered valid in the cache for a TIdDNSResolver object instance.

TTL does not apply to authoritative data in a DNS zone, but can timeout by use of refreshing policies for the zone. TTL is assigned by the administrator for the zone where the data originates.

While short TTLs can be used to minimize caching, and a zero TTL prohibits caching, the realities of Internet performance suggest that these times should be on the order of days for the typical host. If a change can be anticipated, the TTL can be reduced on the DNS server prior to the change to minimize inconsistency during the change, and then increased back to its former value following the change.