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DEMO: Tracert

Traceroute is a network diagnostic tool that maps the path data takes to reach a destination, revealing each hop along the route and the latency at each point. Understanding how to read traceroute output helps identify where delays or bottlenecks exist within a network path.

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About this video

Traceroute is a network diagnostic utility that reveals the full path packets take between a local machine and a remote destination, along with the latency introduced at each intermediate hop. It works by transmitting a series of packets with incrementally increasing Time to Live values, starting at one. Each router that receives a packet decrements the TTL and, when that value hits zero, returns a response to the sender. That response exposes the router's IP address and the round-trip time for that leg of the journey, allowing the complete path to be reconstructed hop by hop. The syntax differs slightly by operating system: Windows uses tracert followed by a hostname or IP address, while Linux uses the command traceroute. Interpreting traceroute output goes beyond simply confirming that a destination is reachable. Each hop typically returns three latency measurements representing three separate probe packets, and comparing those values across consecutive hops makes it straightforward to isolate segments of the path where performance degrades. A jump in latency between two adjacent hops points to congestion, a misconfigured device, or a physically slow link at that specific point in the network. The total hop count and the IP addresses logged along the route also provide useful context for understanding network topology and identifying the autonomous systems or service providers handling traffic at each stage.

What you'll learn

What's covered

Trace Route Tool

Aligned to

CompTIA Network+
5.5 Given a scenario, use the appropriate tool or protocol to solve networking issues.
Cisco CCNA
1.6 Configure and verify IPv4 addressing and subnetting
Cisco CCST Networking
5.3 Run basic diagnostic commands and interpret the results
CompTIA A+ Core 1
2.8 Given a scenario, use networking tools.

Key terms

Time to Live
TTL
A value in a packet that limits its lifespan on a network, preventing it from circulating indefinitely.
Internet Control Message Protocol
ICMP
A network layer protocol used to send error messages and operational information about network conditions.
Latency
The time delay between sending a request and receiving a response over a network.
Router
A network device that forwards data packets between networks based on IP addresses.
traceroute
A Linux command-line tool that maps the path packets take to a destination host by displaying each intermediate hop and its latency.

Transcript

To do traceroute, what we are going to have to do is pull up a command prompt. So I am going to hit Windows and type cmd and hit enter to bring up a command prompt.

Now, in Linux I would just type out traceroute and then wherever I am trying to trace to. In Windows I am going to do tracert instead. With tracert I just type in the address that I want to go to, or in this case I will type in Google, and let us see what the path is to Google, and hit enter.

What Is Happening Behind The Scenes

Now as I am doing this, what is happening is that it is sending out a ping, and it is sending out a ping with a time to live of one. Then it hits the router, and the router replies back and says, well, you have reached your limit of hop counts, and it took two milliseconds. It is showing two milliseconds for that. Then it sends out another ping with a hop count of one and it comes back, and it took one millisecond to get back. Then it sent out a third ping. All these times it is trying to hit www.google.com, but the time to live is just one. So it sends out three of these ping requests and it gets a reply back from the router three times. So now we generally understand that it is one to three milliseconds, which is pretty short, to get a reply back.

Then it sends out a ping with a time to live of two. So then it gets to the router, the router sends it on off to the internet service provider, and the internet service provider responds back and says, you ran out of hops, you hit your hop limit. And so that took 12 milliseconds to get back. Then my machine sent out another ping and it took 11 milliseconds to get it back. Then it sent another ping and it took 12 milliseconds to get back. So roughly around 11 or 12 milliseconds to get to my internet service provider.

Next we see the next hop. It sent out another reply address, but this time the time to live was three, and it came back with, now, what looks like a Comcast router that is right here.

Reading The Results

So it goes through this and tests out all of the hops in between, and how long it took to get information back from each of these machines. The whole total round trip is about 17, 16, 15 milliseconds to get to the final destination and get a response back.

So most of that time is really just in the first hop, just for me to get to my internet service provider. That took most of the time there. And then a little bit of time, it looks like 124, to this connection right here. So something with this connection is a little bit slower, it looks like, because that is anywhere from about 12 to 14 milliseconds. Very similar to this one right here, 12 to 14 milliseconds, but the next hop was 16 to 20 milliseconds. So something about that hop took a little bit more time with it.

And then the other piece of information I can get from this is that I get the IP addresses of each of these destinations, and then I get a total number of hops. So there are 12 hops to get to www.google.com.

That is traceroute, and it allows us to map things out and kind of see what our paths are and where our delay is at, which we identified here: two delays, between hop one and two, and the delay between hop six and seven looks like it is the other one.

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