8. Time to Live (TTL)

The definition of values appropriate to the TTL field in STD 13 is not as clear as it could be, with respect to how many significant bits exist, and whether the value is signed or unsigned. It is hereby specified that a TTL value is an unsigned number, with a minimum value of 0, and a maximum value of 2147483647. That is, a maximum of 2^31 - 1. When transmitted, this value shall be encoded in the less significant 31 bits of the 32 bit TTL field, with the most significant, or sign, bit set to zero.

Implementations should treat TTL values received with the most significant bit set as if the entire value received was zero.

Implementations are always free to place an upper bound on any TTL received, and treat any larger values as if they were that upper bound. The TTL specifies a maximum time to live, not a mandatory time to live.