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The engineers who first designed the Internet Protocol recognized that due to the nature of how routing works on an internetwork, there was always a danger that a datagram might get ?lost in the system? and spend too much time being passed from one router to another. They included in IPv4 datagrams a field called Time To Live, which was intended to be set to a time value by the device sending the datagram, and used as a timer to cause the discard of the datagram if it took too long to get it to its destination.
Eventually, the meaning of this field changed so it was used not as a time in seconds but a number of hops through which the datagram was allowed to be sent. In IPv6, the new meaning of this field was formalized when it was renamed Hop Limit. Regardless of name, the field still has the same basic purpose: it restricts how long a datagram can exist on an internetwork by limiting the number of times routers can forward it. More