traceroute for path tracing in Linux CLI - Step-by-Step Execution

Concept Flow - traceroute for path tracing

Start traceroute command

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Send packet with TTL=1

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Receive response from first router

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Increase TTL by 1

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Send packet with new TTL

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Receive response from next router

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Repeat until destination reached or max hops

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Display full path

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End

Traceroute sends packets with increasing TTL to find each router on the path to the destination, showing the route step-by-step.

Execution Sample

Linux CLI

traceroute example.com

# Shows each hop from your computer to example.com

This command traces the path packets take from your computer to example.com, listing each router along the way.

Execution Table

Step	TTL Value	Packet Sent	Response Received From	Action	Output
1	1	Packet with TTL=1	Router 1 IP	Print hop 1 info	1 192.168.1.1 1.123 ms 1.045 ms 1.010 ms
2	2	Packet with TTL=2	Router 2 IP	Print hop 2 info	2 10.0.0.1 10.234 ms 10.198 ms 10.150 ms
3	3	Packet with TTL=3	Router 3 IP	Print hop 3 info	3 172.16.0.1 20.345 ms 20.300 ms 20.250 ms
4	4	Packet with TTL=4	example.com IP	Print hop 4 info	4 93.184.216.34 30.456 ms 30.400 ms 30.350 ms
5	5	Packet with TTL=5	* * *	No response, stop	* * *
Exit	-	-	-	-	Destination reached or max hops exceeded

💡 Stops when destination responds or max hops reached; here destination responded at TTL=4.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
TTL	1	2	3	4	5	5	Stopped
Current Hop IP	None	192.168.1.1	10.0.0.1	172.16.0.1	93.184.216.34	*	Destination reached
Response Time (ms)	None	1.123	10.234	20.345	30.456	*	N/A

Key Moments - 3 Insights

Why does traceroute increase the TTL value with each packet?

Increasing TTL lets each packet reach one hop further. This is shown in execution_table rows where TTL goes from 1 to 5, revealing each router step-by-step.

What does it mean when traceroute shows '* * *' for a hop?

It means no response was received from that hop. In the execution_table row 5, TTL=5 shows '* * *', indicating no reply, so traceroute stops.

How does traceroute know it reached the destination?

When the response comes from the destination IP, as in row 4 of execution_table, traceroute stops because the path is complete.

Visual Quiz - 3 Questions

Look at the execution_table, what is the TTL value when the response is from example.com?

A 4

B 3

C 5

D 1

💡 Hint

Check the 'TTL Value' column where 'Response Received From' is example.com IP in execution_table row 4.

At which step does traceroute stop sending packets?

A After step 3

B After step 5

C After step 4

D After step 1

💡 Hint

Look at the exit_note and the last successful response in execution_table.

If the router at TTL=3 did not respond, what would the output show at step 3?

A Router 3 IP with times

B * * *

C Destination IP

D No output

💡 Hint

Refer to execution_table row 5 where no response shows '* * *'.

Concept Snapshot

traceroute command sends packets with increasing TTL
Each TTL reveals one more router on the path
Stops when destination replies or max hops reached
Shows IP and response times for each hop
'* * *' means no reply from that hop
Useful to find network path and delays

Full Transcript

Traceroute works by sending packets with a time-to-live (TTL) starting at 1. Each router along the path decreases TTL by 1. When TTL reaches zero, the router replies with its IP. Traceroute increases TTL step-by-step to discover each router on the path to the destination. It stops when the destination replies or the max hops limit is reached. Output shows each hop's IP and response times. If a router does not reply, traceroute shows '* * *'. This helps visualize the path and delays in the network.