ifconfig and ip addr in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of the command ifconfig eth0 if the interface is down?

You run ifconfig eth0 on a Linux system where the network interface eth0 is currently disabled. What will the output show?

Linux CLI

ifconfig eth0

A Returns an error: 'eth0: error fetching interface information: Device not found'

B Displays interface details including 'UP' flag and IP address

C Shows interface details but without 'UP' flag and no IP address assigned

D Shows only the MAC address and no other information

💡 Hint

Think about what happens when an interface is down but still exists.

When an interface is down, ifconfig still shows its details but without the 'UP' flag and usually no IP address assigned.

💻 Command Output

intermediate

What does ip addr show dev eth0 display when the interface has multiple IP addresses?

You run ip addr show dev eth0 on a system where eth0 has two IPv4 addresses assigned. What will the output include?

Linux CLI

ip addr show dev eth0

A Both IP addresses are listed under the interface with their labels

B Only the MAC address and interface name are shown

C An error message about multiple IP addresses

D Only the primary IP address is shown

💡 Hint

Think about how ip addr handles multiple addresses.

ip addr show lists all IP addresses assigned to the interface, each with its own label.

📝 Syntax

advanced

Which command correctly assigns the IP address 192.168.1.10/24 to interface eth0 using ip?

Choose the correct syntax to add the IP address 192.168.1.10 with subnet mask 255.255.255.0 to the interface eth0.

A ip addr assign 192.168.1.10/24 to eth0

B ip add addr 192.168.1.10 dev eth0/24

C ip address set 192.168.1.10/24 eth0

D ip addr add 192.168.1.10/24 dev eth0

💡 Hint

Remember the order: ip addr add [address] dev [interface]

The correct syntax is ip addr add [IP]/[prefix] dev [interface]. Other options are invalid commands.

🔧 Debug

advanced

Why does the command ifconfig eth0 192.168.1.10 netmask 255.255.255.0 up fail with 'SIOCSIFADDR: Operation not permitted'?

You run ifconfig eth0 192.168.1.10 netmask 255.255.255.0 up but get the error 'SIOCSIFADDR: Operation not permitted'. What is the most likely cause?

A You need root or sudo privileges to change network settings

B The IP address format is incorrect

C The interface eth0 does not exist

D The netmask 255.255.255.0 is invalid

💡 Hint

Think about permissions required for network configuration.

Changing IP addresses requires administrative privileges. Without sudo or root, the operation is denied.

🚀 Application

expert

How to script a check that prints all active interfaces with their IPv4 addresses using ip addr?

You want a script that lists only interfaces that are UP and shows their IPv4 addresses in a simple format: interface: IP. Which command pipeline achieves this?

A ip -4 addr show up | awk '/inet/ {print $2}'

B ip -o -4 addr show up | awk '{print $2 ":" $4}'

C ip addr show | grep 'state UP' -A 2 | grep inet | awk '{print $2}'

D ifconfig | grep 'inet ' | awk '{print $1 ":" $2}'

💡 Hint

Use ip -o -4 addr show up for one-line output per address.

Option B uses the correct flags for IPv4, one-line output, filters UP interfaces, and formats output as 'interface: IP'. Others either miss interface names or include extra lines.

Practice

1. What is the main purpose of the ifconfig and ip addr commands in Linux?

easy

A. To manage user accounts

B. To edit text files in the system

C. To monitor CPU usage

D. To display network interface details and IP addresses

Solution

1. Step 1: Understand command purpose

   The commands ifconfig and ip addr are used to show details about network interfaces and their IP addresses.

2. Step 2: Eliminate unrelated options

   Options about editing files, managing users, or CPU monitoring do not relate to network interfaces.

3. Final Answer:

   To display network interface details and IP addresses -> Option D

4. Quick Check:

   Network info = C [OK]

Hint: Remember: both commands show network info, not files or users [OK]

Common Mistakes:

• Confusing network commands with file editing tools
• Thinking these commands manage users
• Assuming they monitor CPU or memory

2. Which of the following is the correct syntax to display all IP addresses using the ip command?

easy

A. ip address list all

B. ip show addr

C. ip addr show

D. ip display ip

Solution

1. Step 1: Recall correct command syntax

   The correct syntax to show IP addresses is ip addr show or simply ip addr.

2. Step 2: Check other options for errors

   Options B, C, and D use incorrect order or invalid keywords.

3. Final Answer:

   ip addr show -> Option C

4. Quick Check:

   Correct syntax = A [OK]

Hint: Remember: 'ip addr show' is the standard order [OK]

Common Mistakes:

• Swapping 'addr' and 'show' order
• Using invalid keywords like 'display' or 'list all'
• Adding unnecessary words

3. What will be the output of the command ifconfig eth0 if the interface eth0 is up with IP 192.168.1.10 and netmask 255.255.255.0?

medium

A. Shows interface eth0 details including IP 192.168.1.10 and netmask 255.255.255.0

B. Shows only the MAC address of eth0

C. Shows error: interface eth0 not found

D. Shows CPU usage statistics

Solution

1. Step 1: Understand ifconfig eth0 output

   This command displays detailed info about the eth0 interface, including IP address and netmask if the interface is up.

2. Step 2: Eliminate unrelated outputs

   It does not show only MAC address, CPU stats, or error if interface exists and is up.

3. Final Answer:

   Shows interface eth0 details including IP 192.168.1.10 and netmask 255.255.255.0 -> Option A

4. Quick Check:

   ifconfig eth0 shows IP and netmask = D [OK]

Hint: ifconfig with interface name shows full details [OK]

Common Mistakes:

• Expecting only MAC address output
• Assuming error if interface is active
• Confusing with CPU or system stats

4. You run ip addr show eth0 but get no output. What is the most likely reason?

medium

A. The eth0 interface does not exist or is down

B. You need to run the command as root

C. The command syntax is incorrect

D. The IP address is not assigned yet

Solution

1. Step 1: Analyze command behavior

   If ip addr show eth0 returns no output, it usually means the interface eth0 does not exist or is disabled.

2. Step 2: Check other options

   Running as root is not required to show interfaces; syntax is correct; lack of IP alone does not cause no output.

3. Final Answer:

   The eth0 interface does not exist or is down -> Option A

4. Quick Check:

   No output means interface missing/down = B [OK]

Hint: No output usually means interface missing or down [OK]

Common Mistakes:

• Assuming root is needed to view interfaces
• Thinking syntax is wrong
• Confusing no IP with no output

5. You want to write a script that checks if the interface eth1 has an IP address assigned using ip addr. Which command snippet correctly tests this?

hard

A. ifconfig eth1 | grep -q 'inet6 '; then echo 'IP assigned'; else echo 'No IP'; fi

B. if ip addr show eth1 | grep -q 'inet '; then echo 'IP assigned'; else echo 'No IP'; fi

C. ip addr show eth1 | grep -q 'ether '; then echo 'IP assigned'; else echo 'No IP'; fi

D. if ip link show eth1 | grep -q 'UP'; then echo 'IP assigned'; else echo 'No IP'; fi

Solution

1. Step 1: Identify correct IP address check

   The command ip addr show eth1 lists addresses; searching for 'inet ' finds IPv4 addresses assigned.

2. Step 2: Evaluate other options

   ifconfig eth1 | grep -q 'inet6 '; then echo 'IP assigned'; else echo 'No IP'; fi checks IPv6 with ifconfig but question asks for ip addr. ip addr show eth1 | grep -q 'ether '; then echo 'IP assigned'; else echo 'No IP'; fi looks for MAC address ('ether'), not IP. if ip link show eth1 | grep -q 'UP'; then echo 'IP assigned'; else echo 'No IP'; fi checks interface status, not IP assignment.

3. Final Answer:

   if ip addr show eth1 | grep -q 'inet '; then echo 'IP assigned'; else echo 'No IP'; fi -> Option B

4. Quick Check:

   Check 'inet ' in ip addr output = A [OK]

Hint: Search 'inet ' in ip addr output to find IPv4 address [OK]

Common Mistakes:

• Checking MAC address instead of IP
• Using ip link instead of ip addr
• Confusing IPv6 with IPv4 check