The time-to-live (TTL) value is specified in the IP header of a
datagram, and is used to control the number of routers that the
datagram is passed through. Each router that handles the datagram
decrements the TTL value by one. When it drops to zero, a datagram is
returned to the sender, specifying that the TTL has been
exceeded.
Setting this property changes the default TTL value for all
subsequent ICMP datagrams sent by the control, with the default value
being 255. Reading this property returns the value of the TTL field
in the IP header of the last datagram received.