LFCS Networking Practice Test 8 — 15 Questions

Question 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

A system administrator is troubleshooting network connectivity from a Linux server to a remote host at 10.0.0.1. The server has a default gateway of 192.168.1.1. Running `ping 10.0.0.1` fails, but `ping 192.168.1.1` succeeds. The output of `ip route show` shows a default route via 192.168.1.1. Which additional step should the administrator take to further investigate?

Accepted Answer

Run traceroute to 10.0.0.1 to see where packets are dropped.. The ping to the default gateway succeeds, confirming local network and ARP resolution are functional, while the ping to the remote host fails. Running traceroute to 10.0.0.1 will reveal the exact hop where packets are dropped, isolating whether the issue lies in routing beyond the gateway, a firewall along the path, or a missing route on an intermediate router.

Answer

Check the ARP table for 10.0.0.1.

Answer

Verify that the firewall on the remote host allows ICMP.

Answer

Check if the remote host is in the same subnet as the server.

Question 11

A server has multiple IP aliases on eth0. Remote hosts cannot reach the secondary IP addresses. What should the administrator check?

Accepted Answer

The ARP flux settings are configured correctly.. When multiple IP aliases are configured on a single Ethernet interface, the kernel may respond to ARP requests inconsistently, a behavior known as ARP flux. This causes remote hosts to receive conflicting MAC addresses for the secondary IPs, preventing connectivity. Correctly configuring ARP flux settings (e.g., using `arp_ignore=1` and `arp_announce=2` via sysctl) ensures the kernel responds only from the appropriate IP and advertises the correct MAC.

Answer

The server's routing table includes routes for the secondary IPs' subnets.

Answer

The interface is set to NOARP.

Answer

The secondary IPs are in the same subnet as the primary.

Question 12

Which TWO commands can be used to display listening TCP ports on a Linux system?

Accepted Answer

ss -tln. The `ss -tln` command displays listening TCP sockets by using the `-t` flag for TCP, `-l` for listening sockets, and `-n` to show numeric addresses and ports without resolving service names. It reads socket information directly from the kernel's netlink interface, making it the modern replacement for netstat on Linux systems.

Answer

nmap -sT localhost

Answer

iptables -L

Answer

lsof -i TCP

Question 13

Which THREE files or directories are commonly used to configure network interfaces on a RHEL/CentOS system?

Accepted Answer

/etc/resolv.conf. /etc/resolv.conf is the primary configuration file for DNS resolver settings on RHEL/CentOS systems. It specifies the nameserver IP addresses, search domains, and resolver options used by the system's glibc resolver library to perform DNS lookups. Without this file, domain name resolution will fail, making it essential for network interface configuration.

Answer

/etc/rc.d/rc.local

Answer

/etc/nsswitch.conf

Question 14

A system administrator needs to ensure that a Linux server can communicate with other hosts on the same subnet. Which command should be used to verify the IP address and netmask configuration?

Accepted Answer

ip addr show. The `ip addr show` command is the modern, recommended tool in Linux for viewing IP addresses and netmasks (prefix lengths) assigned to network interfaces. It directly displays the configuration needed to verify subnet communication, unlike legacy tools that may not show the netmask clearly or mix routing information.

Answer

netstat -rn

Answer

route -n

Answer

ifconfig

Question 15

A user reports that they cannot reach a remote server by hostname but can reach it by IP address. Which configuration file is most likely misconfigured?

Accepted Answer

/etc/resolv.conf. The /etc/resolv.conf file configures the system's DNS resolver, specifying the nameservers to query for hostname-to-IP resolution. If a user can reach a server by IP but not by hostname, it indicates that DNS resolution is failing, which is most commonly due to a missing or incorrect nameserver entry in /etc/resolv.conf.

Answer

/etc/sysconfig/network

Answer

/etc/hosts

Answer

/etc/nsswitch.conf