ping

--- I wonder what it means TTL = 255 (g), and why this value changes from one machine to another. In some TTL = 31, in other is equal to 128. ---

Control area of ​​the IP packet has a field called TTL (Time To Live) to other computers that indicates how much that package must walk to be discarded.
In each host-level Internet through which passes this package, the number of the TTL field is subtracted from 1 and when it reaches zero, it ceases to be retransmitted. The default number of this field is 30, and serves for the package not be eternally roaming the network if you can not find the right one. A hug