56. Traceroute Utility

• NOTE:

  • traceroute is a Unix/Linux command

  • Windows equivalent is tracert

• traceroute is a computer network tool to determine the route taken by packets across an IP network.

• Works by sending successive batch of packets the specified destination address.

• traceroute increases the time-to-live value of each successive batch of packets sent:

  • The first three packets sent have a time-to-live TTL=1.

  • The next three packets have a TTL=TTL+1, that is, 2, 3, 4, and so on.

  • When a packet passes through a host, normally the host decrements the TTL value by one and forwards the packet to the next host.

• When a packet with a TTL of one reaches a host,

  • the host discards the packet

  • sends an ICMP time exceeded (type 11) packet to the sender.

• The traceroute utility uses returning ICMP packets to produce a list of hosts that the packets have traversed en route to the destination.