traceroute for path tracing in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the traceroute command?

The traceroute command shows the path that packets take from your computer to a destination on the internet or network. It helps find where delays or problems happen.

beginner

What does each line in a traceroute output represent?

Each line shows a 'hop'—a step where your data passes through a router or device on the way to the destination. It lists the device's IP and how long it took to respond.

beginner

How can you run traceroute to trace the path to example.com?

You type traceroute example.com in the terminal and press Enter. The command will then show each hop from your computer to example.com.

intermediate

What does it mean if a traceroute line shows * * * instead of times?

It means the router or device did not respond to the request. This could be due to firewall settings or the device not allowing traceroute packets.

intermediate

Why is traceroute useful for troubleshooting internet problems?

It helps identify where delays or failures happen along the path to a website or server. This helps find if the problem is on your network, your internet provider, or beyond.

What does the traceroute command primarily show?

A The speed of your internet connection

B The path packets take to a destination

C The list of open ports on a server

D The IP address of your computer

traceroute shows the path packets take through routers to reach a destination.

In traceroute output, what does a line with * * * usually mean?

A The router responded quickly

B The destination was reached

C The command failed to run

D The router did not respond

* * * means no response was received from that hop.

Which command would you use to trace the path to google.com?

A traceroute google.com

B ping google.com

C netstat google.com

D ifconfig google.com

traceroute google.com traces the path to google.com.

What information does each hop in traceroute output provide?

A Your computer's IP address

B Website content

C Router IP and response time

D File size of data sent

Each hop shows the router's IP and how long it took to respond.

Why might a traceroute be incomplete or stop early?

A A router blocks traceroute packets

B The internet is too fast

C Your computer is turned off

D The destination is offline

Some routers block traceroute packets, causing incomplete results.

Explain how the traceroute command helps you understand network paths and delays.

Think about how data travels through many devices to reach a website.

Describe what you see in a typical traceroute output and what each part means.

Imagine each line as a stop on a journey your data takes.

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