<P> Time to live (TTL) or hop limit is a mechanism that limits the lifespan or lifetime of data in a computer or network . TTL may be implemented as a counter or timestamp attached to or embedded in the data . Once the prescribed event count or timespan has elapsed, data is discarded or revalidated . In computer networking, TTL prevents a data packet from circulating indefinitely . In computing applications, TTL is commonly used to improve the performance and manage the caching of data . </P> <P> Under the Internet Protocol, TTL is an 8 - bit field . In the IPv4 header, TTL is the 9th octet of 20 . In the IPv6 header, it is the 8th octet of 40 . The maximum TTL value is 255, the maximum value of a single octet . A recommended initial value is 64 . </P>

What does time to live mean in dns