LFCS Practice Test 27 — 15 Questions

Question 1

A system administrator is troubleshooting a DHCP issue on a Linux client. After running 'dhclient -r eth0' and then 'dhclient eth0', the interface does not get an IP address. What command can be used to ensure the DHCP client process is fully released and restarted?

Accepted Answer

dhclient -x eth0 && dhclient eth0. Option D is correct because `dhclient -x eth0` explicitly releases the current lease and terminates the DHCP client process for that interface, ensuring a clean state before restarting with `dhclient eth0`. This avoids issues where a stale process or lease file prevents a fresh DHCP handshake, which can occur with `-r` alone if the client daemon remains running.

Answer

dhclient -s 10.0.0.1 eth0

Answer

dhclient -r eth0 && dhclient -v eth0

Answer

killall dhclient && dhclient eth0

Question 2

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 3

Which THREE statements about Linux network bonding modes are correct? (Choose three.)

Accepted Answer

Mode 0 (balance-rr) can cause out-of-order packet delivery.. Mode 0 (balance-rr) transmits packets in sequential order from the first available slave through the last, then starts over. This round-robin distribution can cause packets belonging to the same TCP session to take different physical paths, leading to out-of-order delivery at the receiver, which may trigger TCP retransmissions and degrade performance.

Answer

Mode 2 (balance-xor) distributes traffic based on packet type.

Answer

Modes 5 and 6 (balance-tlb and balance-alb) require IEEE 802.3ad switch support.

Question 4

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. Option B is correct because 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 5

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 6

After configuring the /etc/network/interfaces file as shown, the administrator runs 'ifup eth0'. Which IP address will be assigned to eth0?

Accepted Answer

192.168.1.100. Option B is correct because the configuration in /etc/network/interfaces specifies a static IP address of 192.168.1.100 with the 'address' directive. When 'ifup eth0' is executed, it reads this file and assigns the configured static IP to the interface, ignoring any DHCP settings.

Answer

192.168.1.1

Answer

No IP assigned

Answer

An IP from DHCP

Question 7

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

Accepted Answer

firewall-cmd --add-service=http --permanent. Option B is correct because 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 8

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

Accepted Answer

ss -tuln. Option A is correct because `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 9

A system administrator needs to configure a static IPv4 address of 192.168.1.100/24 on interface eth0 using NetworkManager. Which command accomplishes this?

Accepted Answer

nmcli con mod eth0 ipv4.addresses 192.168.1.100/24 ipv4.method manual. Option C is correct because `nmcli con mod` modifies an existing connection profile, and setting `ipv4.addresses` along with `ipv4.method manual` is the proper way to assign a static IPv4 address in NetworkManager. The `/24` prefix length is correctly specified as part of the address value, and the manual method disables DHCP for IPv4.

Answer

nmcli dev set eth0 ipv4.address 192.168.1.100/24

Answer

nmcli con up eth0 ipv4.address 192.168.1.100/24

Answer

nmcli con add con-name eth0 type ethernet ipv4.address 192.168.1.100/24

Question 10

Which TWO utilities can be used to configure network bridges on Linux?

Accepted Answer

ip. The `ip` command (from the iproute2 suite) is the modern, recommended tool for configuring network bridges on Linux. It can create, delete, and manage bridge devices (e.g., `ip link add name br0 type bridge`) and enslave interfaces to them, replacing the older `brctl` utility. `brctl` is also correct as it was the traditional tool from the bridge-utils package, still widely used for bridge management.

Answer

route

Answer

nmcli

Answer

ifconfig

Question 11

Which legacy command can still be used to view the IPv4 routing table on a modern Linux system?

Accepted Answer

netstat -r. Option D is correct because `netstat -r` is a legacy command that reads the kernel routing table from `/proc/net/route` and displays it in a human-readable format. It remains available on modern Linux systems for backward compatibility, even though its use is discouraged in favor of `ip route`. The `-r` flag specifically instructs `netstat` to show the routing table.

Answer

ip route show

Answer

route -n

Answer

arp -a

Question 12

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 13

A system administrator runs 'ss -tuln' and sees that port 80 is listening. What does the 'u' option represent?

Accepted Answer

UDP. In the `ss` command, the `-u` option filters output to show only UDP sockets. Since the question shows `ss -tuln`, which combines `-t` (TCP), `-u` (UDP), `-l` (listening), and `-n` (numeric), the `u` specifically represents UDP. This is confirmed by the `ss` man page and standard Linux networking tools.

Answer

User

Answer

Unix sockets

Answer

Unicast

Question 14

A network engineer needs to temporarily disable a network interface eth1 without bringing it down permanently. Which command?

Accepted Answer

ip link set eth1 down. The `ip link set eth1 down` command temporarily disables the eth1 interface by changing its state to DOWN at the kernel level, without making any persistent changes to configuration files. This is the correct approach for a temporary disable because the interface can be re-enabled with `ip link set eth1 up` and will revert to its configured state upon reboot.

Answer

systemctl stop network

Answer

nmcli device disconnect eth1

Answer

ifdown eth1

Question 15

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.. Option C is correct because 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.