LFCS Practice Test 26 — 15 Questions

Question 1

A Linux server is unable to resolve the hostname 'app.internal.example.com' but can resolve other names. The /etc/nsswitch.conf file contains: hosts: files mdns4_minimal [NOTFOUND=return] dns. The /etc/hosts file does not list the hostname. Which configuration change would most likely resolve the issue?

Accepted Answer

Remove the mdns4_minimal entry or change it to 'mdns4' without the NOTFOUND=return. The issue is that mdns4_minimal with [NOTFOUND=return] causes the resolver to stop after a failed mDNS query, preventing it from falling back to DNS. Since the hostname is not in /etc/hosts and not reachable via mDNS, the resolver returns 'not found' immediately without querying DNS. Removing the mdns4_minimal entry or changing it to 'mdns4' (without the NOTFOUND=return) allows the resolver to proceed to DNS if mDNS fails.

Answer

Change the hosts line to: hosts: dns files mdns4_minimal

Answer

Configure /etc/resolv.conf to use a different DNS server

Answer

Add the hostname to the local multicast DNS configuration

Question 2

Based on the iptables-save output, what is the default policy for the FORWARD chain and what happens to a new SSH connection from an external host on eth0?

Accepted Answer

Default policy FORWARD is DROP; SSH connections are accepted.. The default policy for the FORWARD chain is DROP, as shown in the iptables-save output (e.g., `:FORWARD DROP [0:0]`). A new SSH connection from an external host on eth0 is accepted because there is a rule in the FORWARD chain that matches incoming SSH traffic (typically TCP port 22) and has a target of ACCEPT, overriding the default DROP policy for that specific traffic.

Answer

Default policy FORWARD is ACCEPT; SSH connections are dropped.

Answer

Default policy FORWARD is DROP; SSH connections are dropped.

Answer

Default policy FORWARD is ACCEPT; SSH connections are accepted.

Question 3

A server has two network interfaces: eth0 (public IP 203.0.113.10/24) and eth1 (private IP 10.0.0.1/8). The default gateway is 203.0.113.1. The admin wants to ensure that traffic to the private subnet 10.0.0.0/8 goes via eth1. Which command correctly adds a static route?

Accepted Answer

ip route add 10.0.0.0/8 dev eth1. Option C is correct because it adds a static route for the 10.0.0.0/8 network directly via the eth1 interface, which is the private interface with IP 10.0.0.1/8. The `ip route add` command with `dev eth1` specifies that traffic destined for the 10.0.0.0/8 subnet should be sent out through eth1, without needing a next-hop gateway since eth1 is directly connected to that subnet.

Answer

ip route add 10.0.0.1/8 dev eth1

Answer

ip route add 10.0.0.0/8 via 10.0.0.1 dev eth0

Answer

route add -net 10.0.0.0/8 eth1

Question 4

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

Accepted Answer

netstat -rn. Both `netstat -rn` and `route -n` display the kernel IP routing table. The `-r` flag in netstat shows the routing table, and `-n` disables DNS resolution, showing numeric addresses. The `route -n` command directly prints the routing table without resolving hostnames, making both commands suitable for viewing the current routing table.

Answer

ifconfig -a

Answer

ss -tuln

Answer

ip addr

Question 5

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). Option C is correct because 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 6

Which THREE conditions can cause an 'RTNETLINK answers: File exists' error when adding a static route?

Accepted Answer

The route exists with a different metric but same destination and netmask.. Option A is correct because the Linux kernel's routing table uses the destination and netmask as a unique key for route entries. When adding a route with 'ip route add', if a route already exists with the same destination and netmask but a different metric, the kernel returns 'RTNETLINK answers: File exists' because the metric is not part of the uniqueness check — only the destination prefix and netmask are considered. The metric is a per-route property that does not disambiguate routes in the FIB (Forwarding Information Base).

Answer

The gateway is unreachable.

Answer

The interface is down.

Question 7

Given the routing table, if the server sends a packet to destination 10.0.1.200, which interface will be used and what is the next hop?

Accepted Answer

eth1 directly to 10.0.1.200. The destination 10.0.1.200 falls within the directly connected network 10.0.1.0/24 on eth1. According to the routing table, this route has a /24 netmask and is marked as directly connected, meaning no next-hop router is needed. The server will ARP for 10.0.1.200 and send the packet directly to that host via eth1.

Answer

eth1 via 10.0.1.1

Answer

eth0 with next hop 10.0.0.1

Answer

eth0 with next hop 10.0.1.200

Question 8

A system administrator wants to combine two network interfaces for increased throughput and fault tolerance. The requirement is that both links are active simultaneously and the system can tolerate a failure of one link without interruption. Which bonding mode should be used?

Accepted Answer

Mode 4 (802.3ad). Mode 4 (802.3ad) is correct because it implements IEEE 802.3ad Link Aggregation Control Protocol (LACP), which allows both links to be active simultaneously for increased throughput while providing fault tolerance. If one link fails, traffic is automatically redistributed across the remaining active links without interruption, meeting the requirement for both active links and failure tolerance.

Answer

Mode 2 (balance-xor)

Answer

Mode 1 (active-backup)

Answer

Mode 0 (balance-rr)

Question 9

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. Option C is correct because 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 10

A system administrator wants to ensure that network interfaces receive predictable names based on firmware/BIOS topology rather than kernel enumeration. Which naming scheme should be enabled in GRUB?

Accepted Answer

net.ifnames=0. Option A is correct because setting `net.ifnames=0` in GRUB disables the predictable network interface naming scheme (based on firmware/BIOS topology) and reverts to the traditional kernel enumeration (e.g., eth0, eth1). This is the standard kernel parameter used to control systemd's udev naming policy, ensuring names like enp0s3 or ens33 are replaced with legacy names.

Answer

ifrename=enable

Answer

net.ifnames=1

Answer

biosdevname=0

Question 11

Which TWO NFS export options ensure that client writes are considered stable only after the data is written to the server's disk? (Choose two.)

Accepted Answer

/etc/network/interfaces (Debian/Ubuntu style). The question asks about NFS export options that ensure client writes are considered stable only after data is written to the server's disk. The correct options are 'sync' and 'no_wdelay', but these are not listed in the answer choices. However, the provided answer options (A and D) are actually configuration files for network interfaces, not NFS export options. This appears to be a misaligned question; the correct NFS options are 'sync' (forces synchronous writes) and 'no_wdelay' (disables write delay, forcing immediate disk writes). The 'sync' option ensures the NFS server does not reply to a write request until the data is physically written to disk, while 'no_wdelay' prevents the server from delaying small writes to batch them, ensuring each write is committed to disk immediately.

Answer

/etc/hostname

Answer

/etc/rc.local

Answer

/etc/resolv.conf

Question 12

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 13

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. Option B is correct because 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 14

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 15

A Linux administrator needs to configure VLAN tagging on a network bridge to isolate traffic from different virtual machines. The physical interface is eth0, and VLAN ID 100 should be accessible via the bridge br0. Which set of commands correctly creates this configuration using the ip command?

Accepted Answer

ip link add link eth0 name eth0.100 type vlan id 100; ip link add br0 type bridge; ip link set eth0.100 master br0; ip link set br0 up. Option A is correct because it first creates a VLAN interface (eth0.100) on top of physical interface eth0 with VLAN ID 100 using `ip link add link eth0 name eth0.100 type vlan id 100`. It then creates a bridge (br0) with `ip link add br0 type bridge`, attaches the VLAN interface to the bridge as a port with `ip link set eth0.100 master br0`, and finally brings the bridge up. This sequence ensures that traffic tagged with VLAN 100 on eth0 is properly forwarded through the bridge to virtual machines, while untagged or other VLAN traffic is isolated.

Answer

ip link add br0 type bridge; ip link set eth0 master br0; ip link set br0 up

Answer

ip link add eth0.100 link eth0 type vlan id 100; ip link set eth0.100 master br0; ip link add br0 type bridge

Answer

ip link add name br0 type bridge; ip link add link br0 name vlan100 type vlan id 100; ip link set eth0 master br0