LFCS Networking Practice Test 3 — 15 Questions

Question 1

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. `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 2

A server with two network interfaces (eth0 and eth1) needs to be configured as a bridge (br0) to allow KVM virtual machines to share the host's physical network. Which steps are correct?

Accepted Answer

Create bridge br0, add eth0 as port, assign IP to br0, remove IP from eth0.. Bridging requires the physical interface (eth0) to be added as a port to the bridge (br0) without an IP address, while the bridge itself gets the IP address to act as the network layer endpoint. This allows KVM virtual machines connected to br0 to communicate through eth0, which operates at layer 2. Removing the IP from eth0 prevents IP conflicts and ensures all traffic is handled by the bridge.

Answer

Create bridge br0, add eth0 as port, assign IP to eth0, do not assign IP to br0.

Answer

Create bond0 from eth0 and eth1, then add bond0 to bridge br0.

Answer

Create bridge br0, add eth0 and eth1 as bridge ports, assign IP to br0, remove IP from eth0 and eth1.

Question 3

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

Accepted Answer

netstat -r. `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 4

A system administrator needs to configure bonding in active-backup mode. Which line in /etc/sysconfig/network-scripts/ifcfg-bond0 defines the bonding mode and primary interface?

Accepted Answer

BONDING_OPTS="mode=1 primary=eth0 miimon=100". Options A and B are both correct. Both lines use BONDING_OPTS to set the bonding mode and primary interface. Option A uses the numeric mode value 'mode=1', which is the standard numeric representation for active-backup. Option B uses the textual value 'mode=active-backup', which is also valid in many Linux distributions (e.g., RHEL/CentOS). Both include the primary interface (eth0) and the miimon parameter. Options C and D are incorrect because option C uses mode=0 (round-robin) and lacks miimon, and option D omits the primary interface specification.

Answer

BONDING_OPTS="mode=0 primary=eth0"

Answer

BONDING_OPTS="mode=active-backup miimon=100"

Question 5

Which nmcli command creates a VLAN interface with tag 10 on device eth0?

Accepted Answer

nmcli connection add type vlan con-name vlan10 dev eth0 id 10. The `nmcli connection add` command with `type vlan` requires the `dev` option to specify the parent interface (eth0) and the `id` option to set the VLAN tag (10). The `con-name` assigns a name to the connection profile, and the resulting interface will be named automatically (e.g., eth0.10) unless overridden by `ifname`. This creates a VLAN interface that tags frames with ID 10 on the parent device eth0.

Answer

nmcli connection add type vlan con-name vlan10 ifname eth0 id 10

Answer

nmcli device add vlan con-name vlan10 dev eth0 id 10

Answer

nmcli connection add type vlan con-name vlan10 ifname eth0.10

Question 6

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 7

After editing /etc/sysconfig/network-scripts/ifcfg-eth0, the network service fails to start. Which is the best command to investigate?

Accepted Answer

systemctl status NetworkManager. The best command to investigate why the network service fails to start after editing an interface configuration file is `systemctl status NetworkManager`, because it shows the current state, recent log entries, and any error messages from the NetworkManager service. Since NetworkManager is the default network service on modern RHEL/CentOS systems, checking its status directly reveals whether it failed to reload or start, and often includes the specific configuration error.

Answer

nmcli device status

Answer

journalctl -u NetworkManager

Answer

ip link show eth0

Question 8

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

Accepted Answer

ip. Option B (ip) is correct because the iproute2 suite includes the ip link command, which can create and manage bridge interfaces (e.g., ip link add name br0 type bridge and ip link set dev eth0 master br0). Option C (nmcli) is correct because NetworkManager's command-line tool can configure bridges via connection profiles, such as nmcli con add type bridge ifname br0 and nmcli con add type bridge-slave. Option D (brctl) is correct because it is the classic bridge-utils utility specifically designed to create and administer Ethernet bridges (brctl addbr br0, brctl addif br0 eth0). Option A (route) is not correct because it only manipulates the IP routing table and cannot create or manage bridge interfaces. Option E (ifconfig) is not correct because, while it can configure interface addresses and states, it has no native capability to create or manage bridge devices.

Answer

route

Answer

ifconfig

Question 9

Refer to the exhibit. A server is configured with two network interfaces. A user on the 192.168.2.0/24 network reports that they cannot reach the server at IP 10.0.0.5. What is the most likely cause based on the routing table?

Accepted Answer

There is no route on the server to the 192.168.2.0/24 network.. The routing table on the server does not contain a route for the 192.168.2.0/24 network. When the user on that network sends traffic to 10.0.0.5, the server can receive it, but any reply traffic from the server to the 192.168.2.0/24 source address will be dropped because the server has no matching route. Without a route to the source network, the server cannot send return packets, making communication fail.

Answer

The default gateway is misconfigured; it should be 192.168.1.1.

Answer

The server's IP address 10.0.0.5 is not in the same subnet as the default gateway.

Answer

The firewall on eth0 is blocking incoming traffic.

Question 10

Refer to the exhibit. A server has two interfaces: eth0 (public) and eth1 (internal). The firewall zone 'internal' is assigned to eth1. An administrator wants to allow TCP traffic on port 8080 from eth1 to the server. Which command will achieve this without affecting existing rules?

Accepted Answer

firewall-cmd --zone=internal --add-port=8080/tcp. It uses the `--zone=internal` flag to target the correct zone assigned to eth1, and `--add-port=8080/tcp` to open only TCP port 8080 without modifying any existing rules. The command is not `--permanent`, so it applies immediately to the runtime configuration, which is the default behavior when `--permanent` is omitted.

Answer

firewall-cmd --permanent --zone=internal --add-port=8080/tcp

Answer

firewall-cmd --zone=internal --add-service=http --add-port=8080/tcp

Answer

firewall-cmd --zone=public --add-port=8080/tcp

Question 11

Refer to the exhibit. An administrator wants to bring up the eth1 interface using the existing connection. Which command should be used?

Accepted Answer

nmcli connection up eth1. `nmcli connection up eth1` activates the existing NetworkManager connection profile associated with the eth1 interface. This command ensures that the interface is brought up using the stored configuration (e.g., IP addressing, DNS, routes) rather than just setting the link state. NetworkManager manages connections as profiles, and `nmcli connection up` is the proper way to apply a profile to an interface.

Answer

nmcli device connect eth1

Answer

ifup eth1

Answer

ip link set eth1 up

Question 12

A system administrator wants to allow incoming SSH connections from a specific IP range 192.168.10.0/24 using firewalld. Which command should be used?

Accepted Answer

firewall-cmd --zone=public --add-rich-rule='rule family="ipv4" source address="192.168.10.0/24" service name="ssh" accept' --permanent. It explicitly targets the 'public' zone (the default zone for external-facing interfaces) and uses a rich rule to allow SSH traffic only from the 192.168.10.0/24 source IP range. The --permanent flag ensures the rule persists across reloads. This is the precise syntax required by firewalld for source-specific service access.

Answer

firewall-cmd --add-rich-rule='rule family="ipv4" source address="192.168.10.0/24" service name="ssh" accept' --permanent

Answer

firewall-cmd --add-service=ssh --add-source=192.168.10.0/24 --zone=internal --permanent

Answer

firewall-cmd --add-source=192.168.10.0/24 --add-service=ssh --permanent

Question 13

A server has two network interfaces: eth0 (192.168.1.10/24) and eth1 (10.0.0.10/24). The default gateway is 192.168.1.1. The administrator wants traffic to 10.0.1.0/24 to go through eth1's gateway 10.0.0.1. Which command adds this route?

Accepted Answer

Both B and C are correct. Both B and C are valid `ip route add` syntax variations that achieve the same result: adding a route to 10.0.1.0/24 via gateway 10.0.0.1 on interface eth1. The `ip route` command accepts the `via` and `dev` keywords in either order, making both B and C syntactically correct. Option D uses the legacy `route` command with improper syntax (missing `dev` keyword before the interface name), which would fail or produce unexpected behavior.

Answer

ip route add 10.0.1.0/24 via 10.0.0.1 dev eth1

Answer

ip route add 10.0.1.0/24 dev eth1 via 10.0.0.1

Answer

route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.0.0.1 eth1

Question 14

To permanently disable IPv6 on a network interface, which configuration should be added to /etc/sysctl.conf?

Accepted Answer

net.ipv6.conf.all.disable_ipv6 = 1. The sysctl parameter `net.ipv6.conf.all.disable_ipv6 = 1` is the proper kernel interface to globally disable IPv6 on all network interfaces. This setting is applied via the sysctl system, which reads `/etc/sysctl.conf` at boot to configure kernel parameters. The key must use the exact `disable_ipv6` suffix (not `disable`) and the `all` scope ensures the setting applies to every interface, including future ones.

Answer

net.ipv6.conf.all.disable=1

Answer

ipv6.disable=1

Answer

net.ipv6.conf.eth0.disable_ipv6 = 1

Question 15

A server with two network interfaces needs to forward IP packets between them. Which two steps are required to enable IP forwarding? (Choose two.)

Accepted Answer

Run sysctl -p. Option C is correct because enabling IP forwarding persistently requires setting the kernel parameter net.ipv4.ip_forward=1 in /etc/sysctl.conf (or a file under /etc/sysctl.d/), which is the standard configuration file for kernel runtime parameters. Option B is correct because after editing /etc/sysctl.conf, running sysctl -p reloads the settings from that file and applies net.ipv4.ip_forward=1 to the running kernel immediately, activating forwarding without a reboot. Option A is not required because systemctl restart network restarts the network service and does not itself enable the kernel's IP forwarding parameter. Option D is not required because adding a route to the second interface is a routing-table change, not the mechanism that turns on packet forwarding between interfaces. Option E is not the correct parameter for this purpose; net.ipv4.conf.all.forwarding is a per-interface-style forwarding control, whereas the canonical global setting for IPv4 forwarding is net.ipv4.ip_forward.

Answer

Run systemctl restart network

Answer

Add a route to the second interface

Answer

Set net.ipv4.conf.all.forwarding=1