LFCS Networking Practice Test 5 — 15 Questions

Question 1

An administrator needs to permanently set a static IPv4 address 192.168.1.100/24 on interface eth0 using NetworkManager. Which command achieves this?

Accepted Answer

nmcli connection modify eth0 ipv4.addresses 192.168.1.100/24 ipv4.method manual. `nmcli connection modify` is the proper command to permanently change a NetworkManager connection profile, and setting both `ipv4.addresses` and `ipv4.method manual` ensures the static IP is applied and the interface does not fall back to DHCP. Without setting the method to `manual`, NetworkManager may ignore the static address or override it with DHCP.

Answer

nmcli connection modify eth0 ipv4.addresses 192.168.1.100/24

Answer

nmcli device modify eth0 ipv4.addresses 192.168.1.100/24

Answer

nmcli connection modify 'System eth0' ipv4.addresses 192.168.1.100/24 ipv4.method manual

Question 2

A technician configured a new network interface eth1 on a CentOS 7 server but the interface does not obtain an IPv4 address via DHCP. Which of the following is the most likely cause?

Accepted Answer

NetworkManager is not managing the interface (NM_CONTROLLED=no). When NM_CONTROLLED=no is set in the interface configuration file (/etc/sysconfig/network-scripts/ifcfg-eth1), NetworkManager will not manage that interface. Since dhclient is typically invoked by NetworkManager (or by legacy network scripts only if NM_CONTROLLED=yes), the interface will not automatically obtain an IPv4 address via DHCP. On CentOS 7, NetworkManager is the default network service, and disabling its control prevents DHCP client activation.

Answer

The interface MTU is set too high

Answer

SELinux is blocking dhclient

Answer

Firewalld is blocking DHCP ports (67/68)

Question 3

Which tool is the recommended method for persistently configuring network interfaces in RHEL 8?

Accepted Answer

Using nmcli commands. In RHEL 8, NetworkManager is the default networking daemon, and 'nmcli' is the recommended command-line tool for persistently configuring network interfaces. Unlike temporary 'ip' commands, nmcli writes configuration to NetworkManager connection profiles, ensuring changes survive reboots. Red Hat officially deprecates direct editing of ifcfg files in RHEL 8 and uses NetworkManager as the primary interface.

Answer

Using the 'ip' command with persistent flags

Answer

Editing /etc/sysconfig/network-scripts/ifcfg-* files directly

Answer

Using systemd-networkd configuration files

Question 4

A server has two NICs bonded in mode 1 (active-backup). If the active NIC fails, what occurs?

Accepted Answer

Traffic automatically switches to the backup NIC with minimal interruption. In bonding mode 1 (active-backup), only one NIC is active at a time while the other remains in standby. When the active NIC fails, the bonding driver automatically fails over to the backup NIC by reassigning the MAC address and IP to the backup interface, typically within a few milliseconds. This ensures minimal interruption to network traffic without requiring manual intervention.

Answer

Both NICs continue to pass traffic simultaneously

Answer

The bond interface goes down until an administrator intervenes

Answer

The system disables the bond and uses a single NIC

Question 5

Which iptables command allows incoming SSH traffic only from the 10.0.0.0/8 network?

Answer

iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/8 -j ACCEPT

Answer

iptables -P INPUT DROP

Question 6

The command 'ss -tuln' shows port 80 is listening on a server, but a remote client cannot connect via HTTP. What is the most likely cause?

Accepted Answer

A firewall is blocking incoming TCP port 80. The `ss -tuln` command shows that port 80 is in the LISTEN state, which means the HTTP service (e.g., Apache or Nginx) is bound to the port and ready to accept connections. Since the server is listening but the remote client cannot connect, the most likely cause is a firewall (such as iptables, nftables, or a cloud security group) that is blocking incoming TCP SYN packets destined for port 80, preventing the three-way handshake from completing.

Answer

The HTTP service is not running

Answer

The client has a misconfigured default gateway

Answer

The server's /etc/hosts file is misconfigured

Question 7

Which bonding mode provides high availability without requiring switch configuration?

Accepted Answer

mode 1 (active-backup). Mode 1 (active-backup) provides high availability by designating one NIC as active and the others as standby, with automatic failover if the active link fails. It requires no special switch configuration because it does not use any link aggregation protocol or load-balancing algorithm that depends on switch-side settings.

Answer

mode 4 (802.3ad)

Answer

mode 6 (balance-alb)

Answer

mode 0 (balance-rr)

Question 8

A server uses firewalld. Which command permanently allows HTTP traffic?

Accepted Answer

firewall-cmd --add-service=http --permanent. The `--permanent` flag is required to make the rule persist across reboots when using `firewall-cmd`. Without it, the rule is only added to the runtime configuration and will be lost after a firewall reload or system restart. The `--add-service=http` parameter uses the predefined service definition for HTTP (port 80/tcp), which is the proper way to allow HTTP traffic in firewalld.

Answer

firewall-cmd --add-service=http

Answer

firewall-cmd --add-port=80/tcp

Answer

systemctl reload firewalld

Question 9

After editing /etc/resolv.conf to set a custom DNS server, the changes are reverted after reboot. What is the most likely cause?

Accepted Answer

NetworkManager manages DNS and overwrites manual changes. NetworkManager actively manages network interfaces and DNS settings by default on many Linux distributions. When a user manually edits /etc/resolv.conf, NetworkManager detects the change and overwrites it with its own configuration, especially after a reboot or network restart, because it treats the file as a managed resource. This is the most common reason for DNS changes being reverted.

Answer

The DHCP client overwrites resolv.conf on lease renewal

Answer

SELinux reinitializes the file from defaults

Answer

systemd-resolved regenerates the file from configuration

Question 10

Which TWO methods can be used to set a static IPv4 address on a CentOS 7 system? (Choose two.)

Accepted Answer

Use the nmtui utility. Nmtui is a text-based user interface for NetworkManager, which is the default networking service on CentOS 7. It allows you to interactively configure network interfaces, including setting a static IPv4 address, without needing to manually edit configuration files. Option E is correct because the ifcfg-eth0 file in /etc/sysconfig/network-scripts is the traditional, direct configuration method for network interfaces on CentOS 7, where you can set BOOTPROTO=static and define IPADDR, PREFIX, and GATEWAY.

Answer

Run the command 'systemctl set-static-ip eth0 192.168.1.100/24'

Answer

Use 'ip addr add 192.168.1.100/24 dev eth0'

Answer

Edit the /etc/network/interfaces file

Question 11

Which THREE are built-in chains in the iptables filter table? (Choose three.)

Accepted Answer

INPUT. The filter table in iptables is used for packet filtering decisions based on IP addresses, ports, and protocols. Its built-in chains are INPUT (for packets destined for the local system), OUTPUT (for packets originating from the local system), and FORWARD (for packets routed through the system). These three chains allow you to control traffic at different points in the packet flow.

Answer

POSTROUTING

Answer

PREROUTING

Question 12

Which TWO commands can display a list of active TCP connections listening on the system? (Choose two.)

Accepted Answer

ss -tuln. `ss -tuln` displays TCP (`-t`) and UDP (`-u`) sockets in a listening (`-l`) state with numeric (`-n`) addresses and ports, directly showing active TCP listening connections. Option D is correct because `netstat -tuln` performs the same function, listing TCP and UDP listening sockets with numeric output, and is the traditional tool for this purpose.

Answer

nmcli connection show

Answer

ifconfig

Answer

ip route show

Question 13

Refer to the exhibit. The output of 'ip addr show' reveals that eth0 is in state DOWN and has no IPv4 address. Which command is most likely to bring the interface up and obtain an IP via DHCP?

Accepted Answer

ifup eth0. The `ifup` command is a distribution-agnostic tool that reads the interface configuration from files (e.g., `/etc/network/interfaces` on Debian/Ubuntu or `/etc/sysconfig/network-scripts/ifcfg-eth0` on RHEL/CentOS) and brings the interface up while automatically initiating a DHCP client (e.g., dhclient or dhcpcd) to obtain an IPv4 address. This is the standard way to activate a network interface with its configured addressing method, including DHCP, in a single step.

Answer

ip link set eth0 up

Answer

ip route add default via 192.168.1.1 dev eth0

Answer

ip link set dev eth0 up

Question 14

Refer to the exhibit. The /etc/sysconfig/network-scripts/ifcfg-eth0 file contains the above content. After reboot, eth0 still does not obtain an IP via DHCP. What is the most likely missing configuration?

Accepted Answer

TYPE=Ethernet is missing. The `ifcfg-eth0` file is missing the `TYPE=Ethernet` directive. In RHEL/CentOS 7 and later, NetworkManager requires the `TYPE` parameter to correctly identify and manage the interface type. Without it, NetworkManager may ignore the file or fail to apply DHCP settings, even if `BOOTPROTO=dhcp` is present.

Answer

The MTU is not specified

Answer

DNS1 is not set

Answer

The gateway is not defined

Question 15

Refer to the exhibit. The output of 'iptables -L -n' shows the INPUT chain rules. What will happen to an SSH connection attempt from 10.0.0.1?

Accepted Answer

The connection will be accepted. The exhibit shows iptables rules for the INPUT chain. The first rule explicitly accepts SSH (port 22) from 10.0.0.1, so the connection attempt from that source IP will be accepted. Since iptables processes rules sequentially and this rule matches, the packet is accepted immediately without checking subsequent rules or the default policy.

Answer

The connection will be dropped by the first rule

Answer

The connection will be rate-limited

Answer

The connection will be dropped by the default policy