traceroute for path tracing in Linux CLI - Commands & Configuration

Introduction

Sometimes you want to see the path your internet data takes to reach a website or server. traceroute helps you find each step your data travels through, showing where delays or problems happen.

When your website is slow and you want to see which server or router is causing the delay

When you want to check if your connection to a remote server is working properly

When you need to understand the route your data takes across the internet for troubleshooting

When you want to verify if your network traffic is going through expected locations

When you are learning how internet routing works by seeing real paths

Commands

This command starts tracing the path from your computer to example.com, showing each step along the way.

Terminal

traceroute example.com

Expected Output

traceroute to example.com (93.184.216.34), 30 hops max, 60 byte packets

 1  192.168.1.1 (192.168.1.1)  1.123 ms  0.987 ms  1.045 ms

 2  10.10.10.1 (10.10.10.1)  10.234 ms  10.456 ms  10.678 ms

 3  203.0.113.1 (203.0.113.1)  20.345 ms  20.567 ms  20.789 ms

 4  198.51.100.1 (198.51.100.1)  30.123 ms  30.345 ms  30.567 ms

 5  93.184.216.34 (93.184.216.34)  40.123 ms  40.345 ms  40.567 ms

→

-m - Set the maximum number of hops traceroute will try

→

-w - Set the time to wait for a response from each probe

This command limits the trace to 5 hops to avoid long output if the destination is far away.

Terminal

traceroute -m 5 example.com

Expected Output

traceroute to example.com (93.184.216.34), 5 hops max, 60 byte packets

 1  192.168.1.1 (192.168.1.1)  1.123 ms  0.987 ms  1.045 ms

 2  10.10.10.1 (10.10.10.1)  10.234 ms  10.456 ms  10.678 ms

 3  203.0.113.1 (203.0.113.1)  20.345 ms  20.567 ms  20.789 ms

 4  198.51.100.1 (198.51.100.1)  30.123 ms  30.345 ms  30.567 ms

 5  93.184.216.34 (93.184.216.34)  40.123 ms  40.345 ms  40.567 ms

→

-m - Limits the maximum hops to trace

This command sets the wait time for each response to 2 seconds, useful if some hops are slow to respond.

Terminal

traceroute -w 2 example.com

Expected Output

traceroute to example.com (93.184.216.34), 30 hops max, 60 byte packets

 1  192.168.1.1 (192.168.1.1)  1.123 ms  0.987 ms  1.045 ms

 2  10.10.10.1 (10.10.10.1)  10.234 ms  10.456 ms  10.678 ms

 3  203.0.113.1 (203.0.113.1)  20.345 ms  20.567 ms  20.789 ms

 4  198.51.100.1 (198.51.100.1)  30.123 ms  30.345 ms  30.567 ms

 5  93.184.216.34 (93.184.216.34)  40.123 ms  40.345 ms  40.567 ms

→

-w - Sets the wait time for each probe response

Key Concept

If you remember nothing else from traceroute, remember: it shows each step your data takes to reach a destination, helping find where delays or problems happen.

Common Mistakes

Running traceroute without root or sudo on some systems

Traceroute may fail or show incomplete results because it needs permission to send certain packets.

Run traceroute with sudo if needed, like 'sudo traceroute example.com', or use options that don't require root.

Using traceroute on a destination that blocks ICMP or UDP packets

Some servers or firewalls block traceroute packets, causing timeouts or missing hops.

Try using traceroute with TCP mode (if supported) or check connectivity with other tools like ping.

Ignoring the maximum hops limit and getting very long output

Traceroute can produce too much output if the path is long, making it hard to read.

Use the -m flag to limit hops, for example 'traceroute -m 10 example.com'.

Summary

Use 'traceroute example.com' to see the path your data takes to reach example.com.

Use flags like -m to limit the number of hops and -w to set wait time for responses.

Run traceroute with proper permissions and be aware some servers may block traceroute packets.

Practice

1. What is the main purpose of the traceroute command in Linux?

easy

A. To display current network connections

B. To list all files in a directory

C. To change the IP address of the system

D. To show the path data takes to reach a destination

Solution

1. Step 1: Understand traceroute function

   The traceroute command traces the route packets take to reach a network host.

2. Step 2: Compare options

   Options A, B, and D describe unrelated commands or functions.

3. Final Answer:

   To show the path data takes to reach a destination -> Option D

4. Quick Check:

   Traceroute purpose = show path [OK]

Hint: Traceroute maps network path hops quickly [OK]

Common Mistakes:

• Confusing traceroute with ping
• Thinking traceroute changes network settings
• Mixing traceroute with file commands

2. Which of the following is the correct syntax to run traceroute to example.com with a maximum of 5 hops?

easy

A. traceroute -m 5 example.com

B. traceroute -max 5 example.com

C. traceroute --maxhops=5 example.com

D. traceroute -h 5 example.com

Solution

1. Step 1: Recall traceroute max hops option

   The option -m sets the max number of hops in traceroute.

2. Step 2: Check syntax correctness

   Only traceroute -m 5 example.com uses the correct option and format.

3. Final Answer:

   traceroute -m 5 example.com -> Option A

4. Quick Check:

   Max hops option = -m [OK]

Hint: Use -m to limit hops in traceroute [OK]

Common Mistakes:

• Using -max or --maxhops which are invalid
• Confusing -h (help) with hop limit
• Placing options after the hostname

3. What will be the output of the command traceroute -n 8.8.8.8?

medium

A. It shows an error because -n is invalid

B. It shows the route to 8.8.8.8 with hostnames only, no IP addresses

C. It shows the route to 8.8.8.8 with IP addresses only, no hostnames

D. It shows the route with both hostnames and IP addresses

Solution

1. Step 1: Understand the -n option in traceroute

   The -n option disables hostname resolution and shows IP addresses only.

2. Step 2: Analyze output format

   Therefore, the output will list IP addresses without hostnames.

3. Final Answer:

   It shows the route to 8.8.8.8 with IP addresses only, no hostnames -> Option C

4. Quick Check:

   -n means no hostname lookup [OK]

Hint: -n shows IPs only, no names [OK]

Common Mistakes:

• Thinking -n shows hostnames
• Assuming -n causes error
• Expecting both IP and hostname with -n

4. You run traceroute -m 3 example.com but it shows more than 3 hops. What is the likely cause?

medium

A. The -m option was ignored because of a syntax error

B. Traceroute always shows all hops regardless of -m

C. The command is correct; traceroute shows up to 3 hops only

D. The hostname resolves to multiple IPs causing extra hops

Solution

1. Step 1: Check syntax of the command

   The correct syntax requires a space between -m and the number, so -m 3 is correct.

2. Step 2: Consider possible syntax errors

   If the option was typed incorrectly (like -m3 without space), traceroute may ignore it and show default hops.

3. Step 3: Evaluate other options

   Traceroute does not always ignore -m; it respects it if syntax is correct. Multiple IPs do not increase hops count.

4. Final Answer:

   The -m option was ignored because of a syntax error -> Option A

5. Quick Check:

   Syntax error causes option ignore [OK]

Hint: Check option syntax carefully for -m [OK]

Common Mistakes:

• Using -m3 without space causing ignore
• Assuming traceroute ignores -m always
• Confusing hops with IP resolution count

5. You want to trace the path to example.com but skip hostname lookups and limit hops to 4. Which command achieves this?

hard

A. traceroute -m 4 -h example.com

B. traceroute -n -m 4 example.com

C. traceroute --no-hostname --max-hops=4 example.com

D. traceroute -4 -n example.com

Solution

1. Step 1: Identify options for skipping hostname and limiting hops

   -n skips hostname lookup; -m 4 limits hops to 4.

2. Step 2: Verify option correctness and order

   traceroute -n -m 4 example.com uses both correctly. traceroute -m 4 -h example.com uses invalid -h. traceroute --no-hostname --max-hops=4 example.com uses non-standard options. traceroute -4 -n example.com limits to IPv4 but not hops.

3. Final Answer:

   traceroute -n -m 4 example.com -> Option B

4. Quick Check:

   -n and -m 4 combined = correct command [OK]

Hint: Combine -n and -m for no hostname and hop limit [OK]

Common Mistakes:

• Using -h instead of -m for hops
• Assuming --no-hostname is valid
• Confusing -4 (IPv4) with hop limit