Time to live For the 1969 French film, see Time to Live (film) . Time to live ( TTL ) or hop limit is a mechanism which 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. IP packets 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. [1] [2] The time-to-live value can be thought of as an upper bound on the tim...