The Time to Live field is required in an IP Packet so that a Router( Layer 3 Network device) knows how long the packet has been in the network for and if it should discard it due to exceeding its limit, which can be a value between 1 and 255.
In Ipv4 the 8 bit field is called Time to Live , but for IPv6 its is called Hop Limit field as it was often referred to in IPv4, both the TTL and Hop limit achieve the same results which is to stop a packet looping the network by decrementing their value by 1 after each hop with a maximum value of 255
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