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.