 Traceroute sends packets with TTL values that gradually increase from packet to packet, starting with TTL value of one.Routers decrement TTL values of packets by one when routing and discard packets whose TTL value has reached zero, returning the ICMP error message ICMP Time Exceeded.For the first set of packets, the first router receives the packet, decrements the TTL value and drops the packet because it then has TTL value zero.