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How Traceroute Works

Part 1: Start Perform a Traceroute

The basic concept of traceroute is not too difficult to understand. A traceroute simply provide the information about the hosts that data passes through. Note that a traceroute will not show all possible paths (routes) through a network to a destination, and usually only shows the most preferred path. Please read the ICMP and UDP first that discussed in our blog in order to understand traceroute much easier.

Traceroute should NOT be used for tracking latency or packet loss. IT WAS NOT DESIGNED FOR THIS. To track latency or packet loss, use Ping instead.

How Traceroute Works

To see how traceroute work, this is better to illustrate with an example.

Traceroute Scenario:

Suppose Computer A do a traceroute to computer B.

You can perform a traceroute by opening the DOS mode of windows. The command is:

tracert [IP Address of computer B]

Here’s what happen at the beginning:

  • Traceroute program in Computer A will send ICMP packets with specific TTL to an open UDP port on Computer B.
  • The TTL of the first set of packets (3 packets) are set to 1.

The scenario is shown in the diagram below:

how traceroute works

In part 2 of this traceroute tutorial series, we will discuss how the ICMP data packets send through the routers.

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