In the Internet Protocol (IP) Time To Live (TTL) is the lifetime of the data being passed over the network before the information is dropped. This is to prevent an infinite loop. Is is defined as the number of hops a packet can go before being discarded. Each time an OSI layer 3 (routing) device handles a packet it deducts the TTL value of the packet by one. If a layer 3 device encounters a TTL of 0 the packet will be discarded. For IPv6 the TTL field has been renamed to hop limit.
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.