Traceroute is a TCP/IP utility which allows the user to determine the route packets take to reach a particular host. Traceroute works by increasing the "time to live" value of each successive packet sent. The first packet has a time to live (TTL) value of one, the second two, and so on. When a packet passes through a host, normally the host decrements the TTL value by one, usually, and forwards the packet to the next host. When a packet with a TTL of one reaches a host, the host discards the packet and sends an ICMP time exceeded (type 11) packet to the sender. The traceroute utility uses these returning packets to produce a list of hosts that the packets have traversed en route to the destination.