LFCS Networking Practice Test 4 — 15 Questions

Question 1

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 2

After configuring iptables rules on a Linux server, a junior administrator notices that incoming SSH connections from a specific IP address (192.168.1.100) are being blocked even though there is a rule to allow all traffic from that IP. The current rule set is: 1. -A INPUT -s 192.168.1.100 -j ACCEPT; 2. -A INPUT -p tcp --dport 22 -j DROP. What is the most likely reason for the block?

Accepted Answer

The DROP rule for port 22 appears before the ACCEPT rule for the IP.. Option C is correct because iptables processes rules in sequential order, and the first matching rule determines the packet's fate. In this rule set, the DROP rule for TCP port 22 is listed second, but since it is the first rule that matches SSH traffic from 192.168.1.100 (the ACCEPT rule matches the source IP but not the destination port, so it does not match SSH packets specifically), the DROP rule is applied before the ACCEPT rule can take effect. The ACCEPT rule for the IP address would only match non-SSH traffic from that IP, while SSH packets are dropped by the subsequent port-based rule.

Answer

The IP address is being matched by a conntrack rule instead.

Answer

The ACCEPT rule for the IP uses the wrong chain.

Answer

The SSH service is listening only on IPv6.

Question 3

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 4

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 5

A server running Ubuntu 20.04 uses netplan for network configuration. The admin wants to set a static IP address 10.0.0.100/24 on interface enp0s3 with gateway 10.0.0.1 and DNS servers 8.8.8.8 and 8.8.4.4. Which YAML configuration is correct?

Accepted Answer

network:
  version: 2
  ethernets:
    enp0s3:
      addresses:
        - 10.0.0.100/24
      gateway4: 10.0.0.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]. Option D is correct because it uses the proper Netplan YAML syntax: `addresses` as a list, `gateway4` for the IPv4 default gateway, and `nameservers` with an `addresses` list. This matches the required static IP 10.0.0.100/24, gateway 10.0.0.1, and DNS servers 8.8.8.8 and 8.8.4.4.

Answer

network:
  version: 2
  ethernets:
    enp0s3:
      addresses:
        - 10.0.0.100/24
      gateway: 10.0.0.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]

Answer

network:
  version: 2
  ethernets:
    enp0s3:
      address: 10.0.0.100/24
      gateway4: 10.0.0.1
      dns-nameservers: 8.8.8.8 8.8.4.4

Answer

network:
  ethernets:
    enp0s3:
      addresses: 10.0.0.100/24
      gateway4: 10.0.0.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]

Question 6

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

Question 7

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 8

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 9

A systemd-networkd managed interface enp1s0 needs to be configured with a static IP address 192.168.1.100/24 and a default gateway via 192.168.1.1. Which .network file configuration is correct?

Accepted Answer

[Match]
Name=enp1s0
[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1. Option C is correct because systemd-networkd uses the `[Match]` section with `Name=` to match the interface, and the `[Network]` section with `Address=` to assign a static IP address and `Gateway=` to set the default gateway. The syntax `Address=192.168.1.100/24` is the proper directive for defining a static IP address in a .network file, and `Gateway=192.168.1.1` correctly specifies the default gateway.

Answer

[Match]
Interface=enp1s0
[Network]
StaticIP=192.168.1.100/24
Gateway=192.168.1.1

Answer

[Link]
Name=enp1s0
[Network]
IPAddress=192.168.1.100/24
Gateway=192.168.1.1

Answer

[Match]
Name=enp1s0
[Network]
Address=192.168.1.100/24
DefaultGateway=192.168.1.1

Question 10

Which TWO commands can be used to display the routing table on a Linux system? (Choose two.)

Accepted Answer

route -n. The `route -n` command displays the kernel IP routing table with numeric addresses, showing destination, gateway, netmask, and interface. The `ip route` command from the iproute2 suite shows the same routing table with more detail and is the modern replacement for `route`. Both are standard tools for viewing routing information on Linux.

Answer

ss -r

Answer

traceroute

Answer

ping -R

Question 11

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 12

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 13

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 14

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 15

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