What is traceroute

Traceroute is a useful tool for determining the response delays and routing loops present in a network pathway across packet switched nodes. It also helps to locate any points of failure encountered while en route to a certain destination. However, in the Internet, Traceroute messages are often blocked by routers in various Autonomous Systems AS , making Traceroute highly inaccurate in many cases.

R2 will respond with a TTL exceeded message. R1 will decrease the TTL from three to two, R2 decrease it from two to one and R3 will have to drop it. R3 sends the TTL exceeded message to R1. We now know that the destination is reachable and we have learned all routers in our path.

Each IP packet that we send is called a probe. Above we have two host computers. H1 is a Windows computer Above we see all routers and the destination. For each hop, traceroute will send three IP packets.

We do this to get a good average of the round trip time for each hop. We can see that this is an ICMP request. When R1 receives this IP packet, it will respond like this:. In the capture file, you will see the two packets above three times. You can take a look at the capture file yourself if you want:. Windows Traceroute. The traceroute commands on Linux works similar to Windows.

It also allows you to specify the number of IP packets probes you want to send. To create a nice clean wireshark capture, I configured it to send only one probe for each hop:. We see we use UDP and the destination port number is R1 will reply to this:. The following example of command syntax shows all of the possible options:. Windows Server More Need more help? Expand your skills. Get new features first.

A subscription to help make the most of your time. Smart assistance features. Ad-free email. Back up and access files across devices. Try one month free. The packet is routed through the first Router R1 , which also decrements the packet value. And it continues like this by incrementing the TTL by 1 until it reaches its destination.

The latency measured for each router in the trace is the time difference between when the message is sent and when the TTL exceeded message is received. So if a router never sends the message, it will not be discovered in the traceroute, but since it is still decrementing the TTL value, it will count as an unknown hop in the trace. This is the end of this first article on traceroutes. Now that you know how traceroutes work, the next articles will cover how to analyze traceroutes, how to read a traceroute, and which information is the most important.

Learn how to identify network issues with Traceroutes by analyzing Traceroute metrics latency, packet loss and hops. Learn how the hostname of a traceroute hops can provide information about the real path from the source to the destination.