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00:00 What is Traceroute
01:07 How Traceroute works
2:45 Handson with traceroute
08:08 Troubleshooting
11:20 Outro

Just like ping, Traceroute uses the ICMP protocol to attempt to establish communication with a remote host.

It can be found on all operating systems and even on switches, routers and firewalls. So it is widely supported.

What traceroute does differently is instead of just telling us if a host can be reached or not, it also tells us every hop that was used to get to the destination host.

A hop is every layer 3 device, typically routers, that our Traceroute message needs to pass through in order to get to the destination.

This can be really handy if you are trying to figure out which direction or which route your traffic is taking.

The way Traceroute collects a list of hops is pretty clever. It uses something called Time To Live or TTL.

TTL is a method of limiting the lifespan of data. For IP packets, the TTL is a counter that decreases for every hop, that the data passes on its way to the destination.

This is where the magic of traceroute comes from.

So let's say we want to reach the Google DNS server 8.8.8.8. When we do a traceroute, our computer will send an ICMP request to 8.8.8.8, but with a TTL value of 1.

That means, that as soon as our request hits the first router, the TTL value will decrease to 0 and the request will be dropped.

The router will respond back to our host with a message saying ‘Timetolive Exceeded’

Our computer then does something clever. It takes note of the router's IP address that just responded.

It then sends the same traceroute request, but this time with a TTL value of 2.

So now, our request hits the first router, decreases the TTL value to 1, and then passes it to the next router.

Again, the TTL value reaches 0 and the message is sent back to the sending computer where we can take note of the second hops IP address.

And this process will continue until either it reaches the destination host, or the traceroute hits its maximum hops which is usually 30.

Ping Explained:    • Ping Command Explained | Real World E...