LFCS Networking Practice Test 2 — 15 Questions

Question 1

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?

Accepted Answer

ip route add 172.16.0.0/16 via 10.0.0.5 dev eth1. Option A is correct because the VPN tunnel endpoint is at 10.0.0.5 on the eth1 network, so traffic to 172.16.0.0/16 must be forwarded via that next-hop IP address using the eth1 interface. The `ip route add` command with `via 10.0.0.5 dev eth1` explicitly sets the gateway and egress interface, ensuring packets are sent through the VPN tunnel.

Answer

ip route add 172.16.0.0/16 via 10.0.0.5 dev eth0

Answer

ip route add 172.16.0.0/16 via 192.168.1.1 dev eth0

Answer

ip route add 172.16.0.0/16 dev eth1

Question 2

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?

Accepted Answer

The gateway 10.0.0.1 is not configured to forward traffic to the internet (no NAT or upstream route).. The routing table shows a default gateway (10.0.0.1) is present, so the issue is not a missing route. Since the server can reach internal resources but not the internet, the most likely cause is that the gateway itself (10.0.0.1) is not configured to perform NAT or does not have an upstream route to forward traffic beyond the local subnet. Without this, packets destined for 8.8.8.8 are sent to the gateway but are then dropped because the gateway has no path to the internet.

Answer

The default gateway is missing from the routing table.

Answer

DNS resolution is not configured.

Answer

A firewall is blocking outbound ICMP traffic.

Question 3

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?

Accepted Answer

nmcli connection modify 'ens33' ipv4.addresses 192.168.1.100/24 ipv4.gateway 192.168.1.1 ipv4.method manual. Option A is correct because it uses the `nmcli` command to modify the NetworkManager connection profile for interface ens33, setting a static IPv4 address with CIDR notation and a default gateway, and explicitly setting the method to 'manual' to ensure the configuration persists across reboots. NetworkManager is the default network service on modern Linux distributions, and `nmcli` is the proper tool for permanent configuration changes.

Answer

ip addr add 192.168.1.100/24 dev ens33

Answer

ifconfig ens33 192.168.1.100 netmask 255.255.255.0 up

Answer

route add default gw 192.168.1.1 ens33

Question 4

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?

Accepted Answer

net.ipv4.ip_forward. Option D is correct because `net.ipv4.ip_forward` is the primary sysctl parameter that controls IP forwarding at the kernel level on Linux systems. Setting it to 1 enables the kernel to forward packets between network interfaces, which is essential for the server to act as a router between the 172.16.0.0/24 and 10.0.0.0/24 subnets.

Answer

net.ipv4.conf.all.forwarding

Answer

net.core.forwarding

Answer

net.ipv4.tcp_forwarding

Question 5

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

Accepted Answer

Editing /etc/network/interfaces. Option C is correct because /etc/network/interfaces is the traditional configuration file used by the ifup/ifdown system on Debian-based distributions to define network interfaces, including IP addresses, netmasks, and gateways. This file is parsed by the ifup command to bring interfaces up with the specified settings, making it a valid method for persistent network configuration.

Answer

Using sysctl to set net.ipv4.conf.eth0.forwarding

Answer

Using systemctl enable network.service

Answer

Editing /etc/sysconfig/network

Question 6

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

Accepted Answer

traceroute. A. traceroute is correct because it uses ICMP (or UDP on some systems) to trace the path packets take to a destination, revealing each hop's IP address and round-trip time. This helps identify routing issues, packet loss, or latency bottlenecks in the network path.

Answer

fdisk

Answer

useradd

Question 7

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

Accepted Answer

53. Option A is correct because port 53 (DNS) is configured to listen only on the loopback interface (127.0.0.1) as shown in the exhibit's output of `ss -tlnp`. The listening address `127.0.0.1:53` indicates the service is bound exclusively to the loopback interface, meaning it is not accessible from external network interfaces.

Answer

22

Answer

443

Answer

80

Question 8

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?

Accepted Answer

The default gateway is unreachable, preventing return traffic from the internet.. The correct answer is C. The server's default gateway (203.0.113.1) is unreachable, as confirmed by the 100% packet loss on ping. This means that although the web server is listening on 0.0.0.0:443 and the firewall allows traffic, any response packets from the server to internet clients must be routed through the default gateway. Without a working gateway, return traffic cannot reach the clients, causing intermittent unreachability from the internet.

Answer

The web server is not listening on the public IP address.

Answer

A firewall rule is blocking incoming HTTPS traffic.

Answer

The private interface eth1 has a misconfigured IP address.

Question 9

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?

Accepted Answer

iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT ACCEPT. Option C is correct because it explicitly allows inbound HTTPS traffic on port 443, permits return traffic for established/related connections (which is essential for the server to communicate with the internal database on port 3306), and sets a default DROP policy on the INPUT chain to block all other inbound traffic. The OUTPUT chain is left with a default ACCEPT policy, allowing the server to initiate outbound connections to the database without additional rules.

Answer

iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP

Answer

iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -P INPUT ACCEPT

Answer

iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT DROP

Question 10

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

Accepted Answer

route -n. The `route -n` command displays the kernel IP routing table with numeric addresses, avoiding DNS resolution for faster output. The `ip route show` command is part of the modern `iproute2` suite and shows the same routing table with more detail and flexibility. Both are standard tools for viewing the current routing table on Linux.

Answer

ss -r

Answer

netstat -r

Answer

ifconfig

Question 11

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?

Accepted Answer

The gateway 192.168.10.1 is not reachable from this host.. The 'Destination Host Unreachable' message indicates that the host has no route to the destination network or the next-hop gateway is not reachable. Since the ping target is 8.8.8.8 (a public IP), the host must forward traffic to its default gateway. If the gateway 192.168.10.1 is not reachable (e.g., due to a down interface, ARP failure, or missing neighbor entry), the kernel will immediately return this ICMP error without attempting to send the packet.

Answer

The IP address 192.168.10.15 is not configured on eth0.

Answer

A firewall is blocking ICMP traffic.

Answer

The default route is missing.

Question 12

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

Question 13

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

Question 14

Match each Linux command to its function.

Question 15

Match each systemd unit type to its purpose.