ICMPv6 Time Exceeded Messages

The engineers who first designed IP 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 (TTL), which was intended to be set to a time value by the device sending the datagram and used as a timer to cause the datagram to be discarded if it took too long to get to its destination.

Eventually, the meaning of this field was changed, so it represented not a time in seconds but the number of hops the datagram was allowed to traverse. In IPv6, the new meaning of this field was formalized when it was renamed ...

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