Networking

A system administrator notices that a web server is not reachable from the internet but is reachable from the internal network. The server's IP is 10.0.1.10/24, and the gateway is 10.0.1.1. Which command should be used to verify the default gateway configuration?

Question 3easymultiple choice

A developer needs to temporarily allow incoming TCP connections on port 8080 for testing. Which iptables command adds a rule to the INPUT chain to accept this traffic?

Question 4hardmultiple choice

A server has two network interfaces: eth0 (10.0.1.10/24, gateway 10.0.1.1) and eth1 (192.168.1.10/24, no gateway). Both are up. The default gateway is set to 10.0.1.1. A ping to 8.8.8.8 fails, but ping to 10.0.1.1 succeeds. What is the most likely cause?

Question 5easymultiple choice

An administrator wants to permanently configure a static IP address on a CentOS 7 system. Which file should be edited?

Question 6mediummultiple choice

A network administrator needs to block all incoming SSH traffic (port 22) from the 192.168.2.0/24 subnet. Which iptables command accomplishes this?

Question 7hardmultiple choice

An administrator is troubleshooting intermittent connectivity issues. Running 'ping -c 100 -i 0.2 10.0.0.1' shows about 5% packet loss. What is the primary purpose of the '-i 0.2' option?

Question 8easymultiple choice

Which command displays the listening UDP ports on a Linux system?

Question 9mediummultiple choice

A server needs to forward packets between two networks: 10.0.1.0/24 on eth0 and 10.0.2.0/24 on eth1. Which sysctl parameter must be enabled?

Question 10mediummulti select

Which TWO commands can be used to display the routing table on a Linux system?

Question 11hardmulti select

Which THREE conditions must be met for a Linux system to function as a router between two networks?

Question 12easymulti select

Which TWO commands can be used to resolve a hostname to an IP address?

Question 13hardmultiple choice

A host with this routing table can ping 10.0.2.1 but cannot ping 8.8.8.8. What is the most likely cause?

Exhibit

Refer to the exhibit.

# ip route show
10.0.1.0/24 dev eth0 proto kernel scope link src 10.0.1.10
10.0.2.0/24 dev eth1 proto kernel scope link src 10.0.2.10
default via 10.0.1.1 dev eth0

Question 14mediummultiple choice

An administrator is unable to SSH into the server from a remote host at 192.168.1.100. Based on the exhibited iptables rules, what is the most likely reason?

Network Topology

Question 15hardmultiple choice

You are a systems administrator for a company that runs a critical application on a Linux server with two network interfaces: eth0 (public IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (private IP 10.0.1.10/24, no gateway). The server must be accessible via SSH (port 22) from the internet, but only from a specific management subnet 198.51.100.0/24. Additionally, the server should be able to access the internet for package updates, but no other inbound traffic from the internet is allowed. The local firewall is iptables. After implementing rules, you find that the server cannot reach the internet (e.g., ping 8.8.8.8 fails), but SSH from the management subnet works. What is the most likely cause?

Question 16mediummultiple choice

Read the full VPN explanation →

You are troubleshooting a Linux server that acts as a router between two networks: 10.0.1.0/24 (eth0) and 10.0.2.0/24 (eth1). IP forwarding is enabled. Hosts on 10.0.1.0/24 can ping the server's eth0 IP (10.0.1.1), but cannot ping hosts on 10.0.2.0/24 (e.g., 10.0.2.10). The server can ping both 10.0.2.10 and 10.0.1.10. The iptables FORWARD chain policy is ACCEPT. What is the most likely cause?

Question 17mediummultiple choice

A company has a server with two network interfaces: eth0 (192.168.1.10/24, gateway 192.168.1.1) and eth1 (10.0.0.10/24, gateway 10.0.0.1). The server needs to reach a remote network 172.16.0.0/16 via a VPN tunnel that terminates at 10.0.0.5 on eth1. Which command should be used to add a route for this traffic?

Question 18hardmultiple choice

A system administrator is troubleshooting network connectivity from a server that can reach internal resources but cannot access the internet. The server's /etc/sysconfig/network-scripts/ifcfg-eth0 file contains: BOOTPROTO=static, IPADDR=10.0.0.10, NETMASK=255.255.255.0, GATEWAY=10.0.0.1. The administrator runs 'ip route show' and sees: default via 10.0.0.1 dev eth0. However, 'ping 8.8.8.8' fails. Which is the most likely cause?

Question 19easymultiple choice

A system administrator needs to permanently configure a network interface named ens33 with a static IPv4 address of 192.168.1.100/24 and a default gateway of 192.168.1.1 on a system using NetworkManager. Which command should the administrator use to achieve this?

Question 20mediummultiple choice

A server has two network interfaces: eth0 (10.0.0.10/24) and eth1 (192.168.1.10/24). The server needs to act as a router for a subnet 172.16.0.0/24, forwarding packets between it and the 10.0.0.0/24 network. Which sysctl parameter must be set to a value of 1 to enable IP forwarding?

Question 21hardmulti select

Which TWO are valid methods to configure a network interface on a Linux system?

Question 22mediummulti select

Which THREE are common tools used for network troubleshooting on Linux?

Question 23easymultiple choice

Based on the exhibit, which port is listening only on the loopback interface?

Exhibit

Refer to the exhibit.

[root@server ~]# ss -tln
State   Recv-Q   Send-Q   Local Address:Port   Peer Address:Port   
LISTEN  0        128      0.0.0.0:22          0.0.0.0:*          
LISTEN  0        128      *:80                *:*                 
LISTEN  0        128      *:443               *:*                 
LISTEN  0        128      127.0.0.1:53        0.0.0.0:*          
LISTEN  0        128      0.0.0.0:8080        0.0.0.0:*

Question 24hardmultiple choice

You are a systems administrator for a company that runs a critical web application on a Linux server. The server has two network interfaces: eth0 (public IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (private IP 10.0.0.10/24). The web server listens on port 443 (HTTPS) and must be accessible from the internet. The server also needs to connect to an internal database server at 10.0.0.50/24 on port 3306. Recently, users reported that the website is intermittently unreachable. You SSH into the server and run 'ss -tln' and see that the web server is listening on 0.0.0.0:443. You check the routing table with 'ip route show' and see: default via 203.0.113.1 dev eth0; 10.0.0.0/24 dev eth1 proto kernel scope link src 10.0.0.10. You also run 'iptables -L -n -v' and see: Chain INPUT (policy ACCEPT), with no rules. However, you notice that the server's default gateway is unreachable from the server itself when you run 'ping 203.0.113.1' (100% packet loss). What is the most likely cause of the intermittent unreachability?

Question 25hardmultiple choice

A company wants to ensure that a web server (IP 192.168.1.10) is accessible from the internet via port 443, but all other inbound traffic should be blocked. The server also needs to communicate with an internal database (IP 10.0.0.50) on port 3306. The default firewall zone is 'public'. Which iptables rules should be applied to the server?

Question 26easymulti select

Read the full NAT/PAT explanation →

Which TWO commands can be used to display the current routing table on a Linux system?

Question 27mediummultiple choice

Based on the exhibit, a system administrator runs ping to 8.8.8.8 and gets 'Destination Host Unreachable'. What is the most likely cause?

Exhibit

Refer to the exhibit.
# ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1a:2b:3c:4d:5e brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.15/24 brd 192.168.10.255 scope global dynamic eth0
       valid_lft 86399sec preferred_lft 86399sec
    inet6 fe80::21a:2bff:fe3c:4d5e/64 scope link
       valid_lft forever preferred_lft forever
# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.10.1    0.0.0.0         UG    0      0        0 eth0
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
# ping -c 1 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 192.168.10.15 icmp_seq=1 Destination Host Unreachable

Question 28mediumdrag order

Read the full DNS explanation →

Order the steps to configure a static IP address on a CentOS/RHEL 7 system using ifcfg files.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 29mediumdrag order

Order the steps to troubleshoot a DNS resolution issue from a Linux client.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 30mediummatching

Match each Linux command to its function.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Search text using patterns

Stream editor for text manipulation

Pattern scanning and processing language

Search for files in a directory hierarchy

Build and execute command lines from input

Question 31mediummatching

Full Practice Test →All Objectives

Match each systemd unit type to its purpose.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Manages a daemon or service

Interprocess communication socket

Schedules and activates other units

Controls mount points

Groups units for synchronization

More Networking questions available in the full practice test.

Continue Practising →

All LFCS Objectives

Objective 4.0

Networking

LFCS Practice Questions

What this objective tests

LFCS Networking — Key Topics

Networking questions on this certification test your ability to deploy and manage networking concepts in scenario-based situations.

Core Networking concepts and how they apply in real-world cloud scenarios.
How to deploy networking correctly and verify the outcome.
Troubleshooting networking issues by interpreting error output and system state.
Cloud best practices and Networking design trade-offs tested by this certification.

Common exam traps

Where candidates lose marks on Networking

⚠Selecting the most expensive service when a simpler managed option meets the requirement.
⚠Forgetting that cloud resources must be explicitly secured — defaults are rarely secure.
⚠Choosing a global service fix when the issue is region-specific.
⚠Overlooking cost implications of cross-region data transfer in architecture questions.

LFCS Networking — Practice Questions

30 questions from this objective

Question 2mediummultiple choice

A system administrator notices that a web server is not reachable from the internet but is reachable from the internal network. The server's IP is 10.0.1.10/24, and the gateway is 10.0.1.1. Which command should be used to verify the default gateway configuration?

Question 3easymultiple choice

A developer needs to temporarily allow incoming TCP connections on port 8080 for testing. Which iptables command adds a rule to the INPUT chain to accept this traffic?

Question 4hardmultiple choice

A server has two network interfaces: eth0 (10.0.1.10/24, gateway 10.0.1.1) and eth1 (192.168.1.10/24, no gateway). Both are up. The default gateway is set to 10.0.1.1. A ping to 8.8.8.8 fails, but ping to 10.0.1.1 succeeds. What is the most likely cause?

Question 5easymultiple choice

An administrator wants to permanently configure a static IP address on a CentOS 7 system. Which file should be edited?

Question 6mediummultiple choice

A network administrator needs to block all incoming SSH traffic (port 22) from the 192.168.2.0/24 subnet. Which iptables command accomplishes this?

Question 7hardmultiple choice

An administrator is troubleshooting intermittent connectivity issues. Running 'ping -c 100 -i 0.2 10.0.0.1' shows about 5% packet loss. What is the primary purpose of the '-i 0.2' option?

Question 8easymultiple choice

Which command displays the listening UDP ports on a Linux system?

Question 9mediummultiple choice

A server needs to forward packets between two networks: 10.0.1.0/24 on eth0 and 10.0.2.0/24 on eth1. Which sysctl parameter must be enabled?

Question 10mediummulti select

Which TWO commands can be used to display the routing table on a Linux system?

Question 11hardmulti select

Which THREE conditions must be met for a Linux system to function as a router between two networks?

Question 12easymulti select

Which TWO commands can be used to resolve a hostname to an IP address?

Question 13hardmultiple choice

A host with this routing table can ping 10.0.2.1 but cannot ping 8.8.8.8. What is the most likely cause?

Exhibit

Refer to the exhibit.

# ip route show
10.0.1.0/24 dev eth0 proto kernel scope link src 10.0.1.10
10.0.2.0/24 dev eth1 proto kernel scope link src 10.0.2.10
default via 10.0.1.1 dev eth0

Question 14mediummultiple choice

An administrator is unable to SSH into the server from a remote host at 192.168.1.100. Based on the exhibited iptables rules, what is the most likely reason?

Network Topology

Question 15hardmultiple choice

You are a systems administrator for a company that runs a critical application on a Linux server with two network interfaces: eth0 (public IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (private IP 10.0.1.10/24, no gateway). The server must be accessible via SSH (port 22) from the internet, but only from a specific management subnet 198.51.100.0/24. Additionally, the server should be able to access the internet for package updates, but no other inbound traffic from the internet is allowed. The local firewall is iptables. After implementing rules, you find that the server cannot reach the internet (e.g., ping 8.8.8.8 fails), but SSH from the management subnet works. What is the most likely cause?

Question 16mediummultiple choice

Read the full VPN explanation →

You are troubleshooting a Linux server that acts as a router between two networks: 10.0.1.0/24 (eth0) and 10.0.2.0/24 (eth1). IP forwarding is enabled. Hosts on 10.0.1.0/24 can ping the server's eth0 IP (10.0.1.1), but cannot ping hosts on 10.0.2.0/24 (e.g., 10.0.2.10). The server can ping both 10.0.2.10 and 10.0.1.10. The iptables FORWARD chain policy is ACCEPT. What is the most likely cause?

Question 17mediummultiple choice

A company has a server with two network interfaces: eth0 (192.168.1.10/24, gateway 192.168.1.1) and eth1 (10.0.0.10/24, gateway 10.0.0.1). The server needs to reach a remote network 172.16.0.0/16 via a VPN tunnel that terminates at 10.0.0.5 on eth1. Which command should be used to add a route for this traffic?

Question 18hardmultiple choice

A system administrator is troubleshooting network connectivity from a server that can reach internal resources but cannot access the internet. The server's /etc/sysconfig/network-scripts/ifcfg-eth0 file contains: BOOTPROTO=static, IPADDR=10.0.0.10, NETMASK=255.255.255.0, GATEWAY=10.0.0.1. The administrator runs 'ip route show' and sees: default via 10.0.0.1 dev eth0. However, 'ping 8.8.8.8' fails. Which is the most likely cause?

Question 19easymultiple choice

A system administrator needs to permanently configure a network interface named ens33 with a static IPv4 address of 192.168.1.100/24 and a default gateway of 192.168.1.1 on a system using NetworkManager. Which command should the administrator use to achieve this?

Question 20mediummultiple choice

A server has two network interfaces: eth0 (10.0.0.10/24) and eth1 (192.168.1.10/24). The server needs to act as a router for a subnet 172.16.0.0/24, forwarding packets between it and the 10.0.0.0/24 network. Which sysctl parameter must be set to a value of 1 to enable IP forwarding?

Question 21hardmulti select

Which TWO are valid methods to configure a network interface on a Linux system?

Question 22mediummulti select

Which THREE are common tools used for network troubleshooting on Linux?

Question 23easymultiple choice

Based on the exhibit, which port is listening only on the loopback interface?

Exhibit

Refer to the exhibit.

[root@server ~]# ss -tln
State   Recv-Q   Send-Q   Local Address:Port   Peer Address:Port   
LISTEN  0        128      0.0.0.0:22          0.0.0.0:*          
LISTEN  0        128      *:80                *:*                 
LISTEN  0        128      *:443               *:*                 
LISTEN  0        128      127.0.0.1:53        0.0.0.0:*          
LISTEN  0        128      0.0.0.0:8080        0.0.0.0:*

Question 24hardmultiple choice

You are a systems administrator for a company that runs a critical web application on a Linux server. The server has two network interfaces: eth0 (public IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (private IP 10.0.0.10/24). The web server listens on port 443 (HTTPS) and must be accessible from the internet. The server also needs to connect to an internal database server at 10.0.0.50/24 on port 3306. Recently, users reported that the website is intermittently unreachable. You SSH into the server and run 'ss -tln' and see that the web server is listening on 0.0.0.0:443. You check the routing table with 'ip route show' and see: default via 203.0.113.1 dev eth0; 10.0.0.0/24 dev eth1 proto kernel scope link src 10.0.0.10. You also run 'iptables -L -n -v' and see: Chain INPUT (policy ACCEPT), with no rules. However, you notice that the server's default gateway is unreachable from the server itself when you run 'ping 203.0.113.1' (100% packet loss). What is the most likely cause of the intermittent unreachability?

Question 25hardmultiple choice

A company wants to ensure that a web server (IP 192.168.1.10) is accessible from the internet via port 443, but all other inbound traffic should be blocked. The server also needs to communicate with an internal database (IP 10.0.0.50) on port 3306. The default firewall zone is 'public'. Which iptables rules should be applied to the server?

Question 26easymulti select

Read the full NAT/PAT explanation →

Which TWO commands can be used to display the current routing table on a Linux system?

Question 27mediummultiple choice

Based on the exhibit, a system administrator runs ping to 8.8.8.8 and gets 'Destination Host Unreachable'. What is the most likely cause?

Exhibit

Refer to the exhibit.
# ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1a:2b:3c:4d:5e brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.15/24 brd 192.168.10.255 scope global dynamic eth0
       valid_lft 86399sec preferred_lft 86399sec
    inet6 fe80::21a:2bff:fe3c:4d5e/64 scope link
       valid_lft forever preferred_lft forever
# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.10.1    0.0.0.0         UG    0      0        0 eth0
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
# ping -c 1 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 192.168.10.15 icmp_seq=1 Destination Host Unreachable

Question 28mediumdrag order

Read the full DNS explanation →

Order the steps to configure a static IP address on a CentOS/RHEL 7 system using ifcfg files.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 29mediumdrag order

Order the steps to troubleshoot a DNS resolution issue from a Linux client.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 30mediummatching

Match each Linux command to its function.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Search text using patterns

Stream editor for text manipulation

Pattern scanning and processing language

Search for files in a directory hierarchy

Build and execute command lines from input

Question 31mediummatching