LFCS Networking — All Questions With Answers

A system administrator notices that a web server is not reachable from the internet but is reachable from the internal network. The server's IP is 10.0.1.10/24, and the gateway is 10.0.1.1. Which command should be used to verify the default gateway configuration?

Question 2easymultiple choice

A developer needs to temporarily allow incoming TCP connections on port 8080 for testing. Which iptables command adds a rule to the INPUT chain to accept this traffic?

Question 3hardmultiple choice

A server has two network interfaces: eth0 (10.0.1.10/24, gateway 10.0.1.1) and eth1 (192.168.1.10/24, no gateway). Both are up. The default gateway is set to 10.0.1.1. A ping to 8.8.8.8 fails, but ping to 10.0.1.1 succeeds. What is the most likely cause?

Question 4easymultiple choice

An administrator wants to permanently configure a static IP address on a CentOS 7 system. Which file should be edited?

Question 5mediummultiple choice

A network administrator needs to block all incoming SSH traffic (port 22) from the 192.168.2.0/24 subnet. Which iptables command accomplishes this?

Question 6hardmultiple choice

An administrator is troubleshooting intermittent connectivity issues. Running 'ping -c 100 -i 0.2 10.0.0.1' shows about 5% packet loss. What is the primary purpose of the '-i 0.2' option?

Question 7easymultiple choice

Which command displays the listening UDP ports on a Linux system?

Question 8mediummultiple choice

A server needs to forward packets between two networks: 10.0.1.0/24 on eth0 and 10.0.2.0/24 on eth1. Which sysctl parameter must be enabled?

Question 9mediummulti select

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

Question 10hardmulti select

Which THREE conditions must be met for a Linux system to function as a router between two networks?

Question 11easymulti select

Which TWO commands can be used to resolve a hostname to an IP address?

Question 12hardmultiple choice

A host with this routing table can ping 10.0.2.1 but cannot ping 8.8.8.8. What is the most likely cause?

Exhibit

Refer to the exhibit.

# ip route show
10.0.1.0/24 dev eth0 proto kernel scope link src 10.0.1.10
10.0.2.0/24 dev eth1 proto kernel scope link src 10.0.2.10
default via 10.0.1.1 dev eth0

Question 13mediummultiple choice

An administrator is unable to SSH into the server from a remote host at 192.168.1.100. Based on the exhibited iptables rules, what is the most likely reason?

Network Topology

Question 14hardmultiple choice

You are a systems administrator for a company that runs a critical application on a Linux server with two network interfaces: eth0 (public IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (private IP 10.0.1.10/24, no gateway). The server must be accessible via SSH (port 22) from the internet, but only from a specific management subnet 198.51.100.0/24. Additionally, the server should be able to access the internet for package updates, but no other inbound traffic from the internet is allowed. The local firewall is iptables. After implementing rules, you find that the server cannot reach the internet (e.g., ping 8.8.8.8 fails), but SSH from the management subnet works. What is the most likely cause?

Question 15mediummultiple choice

Read the full VPN explanation →

You are troubleshooting a Linux server that acts as a router between two networks: 10.0.1.0/24 (eth0) and 10.0.2.0/24 (eth1). IP forwarding is enabled. Hosts on 10.0.1.0/24 can ping the server's eth0 IP (10.0.1.1), but cannot ping hosts on 10.0.2.0/24 (e.g., 10.0.2.10). The server can ping both 10.0.2.10 and 10.0.1.10. The iptables FORWARD chain policy is ACCEPT. What is the most likely cause?

Question 16mediummultiple choice

A company has a server with two network interfaces: eth0 (192.168.1.10/24, gateway 192.168.1.1) and eth1 (10.0.0.10/24, gateway 10.0.0.1). The server needs to reach a remote network 172.16.0.0/16 via a VPN tunnel that terminates at 10.0.0.5 on eth1. Which command should be used to add a route for this traffic?

Question 17hardmultiple choice

A system administrator is troubleshooting network connectivity from a server that can reach internal resources but cannot access the internet. The server's /etc/sysconfig/network-scripts/ifcfg-eth0 file contains: BOOTPROTO=static, IPADDR=10.0.0.10, NETMASK=255.255.255.0, GATEWAY=10.0.0.1. The administrator runs 'ip route show' and sees: default via 10.0.0.1 dev eth0. However, 'ping 8.8.8.8' fails. Which is the most likely cause?

Question 18easymultiple choice

A system administrator needs to permanently configure a network interface named ens33 with a static IPv4 address of 192.168.1.100/24 and a default gateway of 192.168.1.1 on a system using NetworkManager. Which command should the administrator use to achieve this?

Question 19mediummultiple choice

A server has two network interfaces: eth0 (10.0.0.10/24) and eth1 (192.168.1.10/24). The server needs to act as a router for a subnet 172.16.0.0/24, forwarding packets between it and the 10.0.0.0/24 network. Which sysctl parameter must be set to a value of 1 to enable IP forwarding?

Question 20hardmulti select

Which TWO are valid methods to configure a network interface on a Linux system?

Question 21mediummulti select

Which THREE are common tools used for network troubleshooting on Linux?

Question 22easymultiple choice

Based on the exhibit, which port is listening only on the loopback interface?

Exhibit

Refer to the exhibit.

[root@server ~]# ss -tln
State   Recv-Q   Send-Q   Local Address:Port   Peer Address:Port   
LISTEN  0        128      0.0.0.0:22          0.0.0.0:*          
LISTEN  0        128      *:80                *:*                 
LISTEN  0        128      *:443               *:*                 
LISTEN  0        128      127.0.0.1:53        0.0.0.0:*          
LISTEN  0        128      0.0.0.0:8080        0.0.0.0:*

Question 23hardmultiple choice

You are a systems administrator for a company that runs a critical web application on a Linux server. The server has two network interfaces: eth0 (public IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (private IP 10.0.0.10/24). The web server listens on port 443 (HTTPS) and must be accessible from the internet. The server also needs to connect to an internal database server at 10.0.0.50/24 on port 3306. Recently, users reported that the website is intermittently unreachable. You SSH into the server and run 'ss -tln' and see that the web server is listening on 0.0.0.0:443. You check the routing table with 'ip route show' and see: default via 203.0.113.1 dev eth0; 10.0.0.0/24 dev eth1 proto kernel scope link src 10.0.0.10. You also run 'iptables -L -n -v' and see: Chain INPUT (policy ACCEPT), with no rules. However, you notice that the server's default gateway is unreachable from the server itself when you run 'ping 203.0.113.1' (100% packet loss). What is the most likely cause of the intermittent unreachability?

Question 24hardmultiple choice

A company wants to ensure that a web server (IP 192.168.1.10) is accessible from the internet via port 443, but all other inbound traffic should be blocked. The server also needs to communicate with an internal database (IP 10.0.0.50) on port 3306. The default firewall zone is 'public'. Which iptables rules should be applied to the server?

Question 25easymulti select

Read the full NAT/PAT explanation →

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

Question 26mediummultiple choice

Based on the exhibit, a system administrator runs ping to 8.8.8.8 and gets 'Destination Host Unreachable'. What is the most likely cause?

Exhibit

Refer to the exhibit.
# ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1a:2b:3c:4d:5e brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.15/24 brd 192.168.10.255 scope global dynamic eth0
       valid_lft 86399sec preferred_lft 86399sec
    inet6 fe80::21a:2bff:fe3c:4d5e/64 scope link
       valid_lft forever preferred_lft forever
# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.10.1    0.0.0.0         UG    0      0        0 eth0
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
# ping -c 1 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 192.168.10.15 icmp_seq=1 Destination Host Unreachable

Question 27mediumdrag order

Order the steps to configure a static IP address on a CentOS/RHEL 7 system using ifcfg files.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 28mediumdrag order

Order the steps to troubleshoot a DNS resolution issue from a Linux client.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 29mediummatching

Match each Linux command to its function.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Search text using patterns

Stream editor for text manipulation

Pattern scanning and processing language

Search for files in a directory hierarchy

Build and execute command lines from input

Question 30mediummatching

Match each systemd unit type to its purpose.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Manages a daemon or service

Interprocess communication socket

Schedules and activates other units

Controls mount points

Groups units for synchronization

Question 31easymultiple choice

A system administrator needs to configure a static IP address on a CentOS 7 server. Which file should be edited to set the IP address permanently?

Question 32mediummultiple choice

A Linux server cannot reach the internet, but internal LAN connectivity works. The output of 'ip route' shows a default gateway of 192.168.1.1, but pinging 8.8.8.8 fails. What is the most likely cause?

Question 33hardmultiple choice

A company is designing a multi-homed server with two network interfaces: one for internal traffic (eth0) and one for external traffic (eth1). The server must prioritize traffic to the 10.1.0.0/16 network through eth0. What is the best practice to ensure traffic to 10.1.0.0/16 uses eth0?

Question 34easymultiple choice

A user reports that they can access websites by IP address but not by domain name. Which command should the administrator use to diagnose the issue?

Question 35mediummultiple choice

A financial firm requires all internal SSH connections to be encrypted with at least 256-bit ciphers. An administrator is configuring the SSH server. Which configuration line should be added to /etc/ssh/sshd_config?

Question 36hardmultiple choice

A server on a corporate network is intermittently losing connectivity. The administrator runs 'tcpdump -i eth0 icmp' and sees 'ICMP time exceeded in-transit' messages from a router. What is the most likely cause?

Question 37easymultiple choice

An administrator wants to ensure that a service is listening on TCP port 8080 and accessible from remote hosts. Which command will confirm that the service is listening on the correct interface?

Question 38mediummultiple choice

A company deploys a new web server with two network interfaces: one for public access (eth0) and one for database access (eth1). The database server is at 10.0.0.10. The web server's default gateway is via eth0, but traffic to 10.0.0.10 is being routed through eth0 instead of eth1. What is the simplest fix?

Question 39hardmultiple choice

A system administrator needs to securely transfer files between two Linux servers using port 22. The administrator uses the following command: 'scp file.txt user@remote:/tmp/'. The transfer fails with the error 'Permission denied (publickey)'. What is the most likely cause?

Question 40mediummulti select

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

Question 41hardmulti select

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

Question 42easymulti select

Which TWO configuration files are commonly used to set DNS resolver settings on a Linux system?

Question 43mediummultiple choice

Given the routing table output in the exhibit, what will happen when the system tries to send a packet to 10.1.1.1?

Exhibit

Refer to the exhibit.

$ ip route show
192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.10 metric 100
10.0.0.0/8 via 192.168.1.1 dev eth0 proto static metric 100
default via 192.168.1.1 dev eth0 proto static metric 100

Question 44hardmultiple choice

Given the network interface configuration in the exhibit, which command should be run to apply the configuration without rebooting?

Exhibit

Refer to the exhibit.

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.168.1.10
NETMASK=255.255.255.0
GATEWAY=192.168.1.1

Question 45easymultiple choice

Based on the tcpdump output in the exhibit, what can be concluded about the TCP handshake?

Exhibit

Refer to the exhibit.

$ tcpdump -i eth0 -c 5 'port 80'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
11:11:11.111111 IP 10.0.0.1.12345 > 192.168.1.1.80: Flags [S], seq 123, win 29200, options [mss 1460], length 0
11:11:11.222222 IP 192.168.1.1.80 > 10.0.0.1.12345: Flags [S.], seq 456, ack 124, win 28960, options [mss 1460], length 0
11:11:11.333333 IP 10.0.0.1.12345 > 192.168.1.1.80: Flags [.], ack 457, win 29312, length 0

Question 46easymultiple choice

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?

Question 47mediummultiple choice

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?

Question 48hardmultiple choice

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?

Question 49easymultiple choice

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?

Question 50mediummultiple choice

Open the full VLAN trunking answer →

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?

Question 51hardmultiple choice

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?

Question 52easymultiple choice

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?

Question 53mediummultiple choice

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?

Question 54hardmultiple choice

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?

Question 55mediummulti select

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

Question 56hardmulti select

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

Question 57mediummulti select

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.)

Question 58mediummultiple choice

Read the full NAT/PAT explanation →

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?

Network Topology

Question 59hardmultiple choice

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?

Exhibit

Refer to the exhibit.

[root@server ~]# ip route show
10.0.0.0/24 dev eth0 proto kernel scope link src 10.0.0.100 metric 100
10.0.1.0/24 dev eth1 proto kernel scope link src 10.0.1.100 metric 101
default via 10.0.0.1 dev eth0 proto static metric 100

Question 60easymultiple choice

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

Exhibit

Refer to the exhibit.

# /etc/network/interfaces on Debian:
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1

Question 61mediummultiple choice

An administrator needs to permanently set a static IPv4 address 192.168.1.100/24 on interface eth0 using NetworkManager. Which command achieves this?

Question 62hardmultiple choice

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?

Question 63easymultiple choice

Which tool is the recommended method for persistently configuring network interfaces in RHEL 8?

Question 64mediummultiple choice

A server has two NICs bonded in mode 1 (active-backup). If the active NIC fails, what occurs?

Question 65hardmultiple choice

Which iptables command allows incoming SSH traffic only from the 10.0.0.0/8 network?

Question 66easymultiple choice

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?

Question 67mediummultiple choice

Which bonding mode provides high availability without requiring switch configuration?

Question 68hardmultiple choice

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

Question 69mediummultiple choice

After editing /etc/resolv.conf to set a custom DNS server, the changes are reverted after reboot. What is the most likely cause?

Question 70easymulti select

Which TWO methods can be used to set a static IPv4 address on a CentOS 7 system? (Choose two.)

Question 71mediummulti select

Which THREE are built-in chains in the iptables filter table? (Choose three.)

Question 72hardmulti select

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

Question 73mediummultiple choice

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?

Exhibit

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff

Question 74hardmultiple choice

Refer to the exhibit. The /etc/sysconfig/network-scripts/ifcfg-eth0 file contains the above content. After reboot, eth0 still does not obtain an IP via DHCP. What is the most likely missing configuration?

Exhibit

DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
HWADDR=52:54:00:12:34:56

Question 75easymultiple choice

Refer to the exhibit. The output of 'iptables -L -n' shows the INPUT chain rules. What will happen to an SSH connection attempt from 10.0.0.1?

Exhibit

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 ACCEPT     tcp  --  *      *       10.0.0.0/8           0.0.0.0/0            tcp dpt:22
    0     0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:22

Question 76easymultiple choice

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?

Question 77mediummultiple choice

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?

Question 78hardmultiple choice

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?

Question 79easymultiple choice

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

Question 80mediummultiple choice

Open the full VLAN trunking answer →

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?

Question 81hardmultiple choice

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

Question 82easymultiple choice

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

Question 83mediummultiple choice

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

Question 84hardmultiple choice

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

Question 85easymulti select

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

Question 86mediummulti select

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

Question 87hardmulti select

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

Question 88mediummultiple choice

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?

Exhibit

[user@server ~]$ ip route show
default via 10.0.0.1 dev eth0 proto static metric 100 
10.0.0.0/24 dev eth0 proto kernel scope link src 10.0.0.5 metric 100 
10.0.1.0/24 via 10.0.0.2 dev eth0 proto static metric 100 
192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.10 metric 101

Question 89hardmultiple choice

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?

Network Topology

Question 90easymultiple choice

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

Exhibit

[root@server ~]# nmcli connection show
NAME   UUID                                  TYPE      DEVICE 
eth0   a1b2c3d4-...                          ethernet  eth0   
eth1   e5f6g7h8-...                          ethernet  --     
br0    i9j0k1l2-...                          bridge    br0

Question 91easymultiple choice

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?

Question 92easymultiple choice

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?

Question 93mediummultiple choice

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?

Question 94mediummultiple choice

A network interface eth0 is not receiving an IP address via DHCP. Which command can be used to troubleshoot the DHCP client process?

Question 95hardmultiple choice

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?

Question 96hardmultiple choice

Study the full IPv6 explanation →

An administrator is configuring a bridge using iproute2. Which command correctly attaches eth0 to bridge br0?

Question 97easymultiple choice

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

Question 98mediummultiple choice

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

Question 99easymulti select

A system administrator needs to check the firewall rules on a Linux server using firewalld. Which two commands can be used to list the current rules? (Choose two.)

Question 100mediummulti select

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

Question 101hardmulti select

An administrator is troubleshooting DNS resolution and wants to query the SOA record for a domain. Which three commands can be used? (Choose three.)

Question 102easymultiple choice

Read the full NAT/PAT explanation →

You are a Linux administrator for a small company. A developer has deployed a web application on a server with IP 192.168.1.50. The application needs to connect to a database server at 10.0.0.100 on TCP port 3306. Both servers are on the same physical network but different subnets (192.168.1.0/24 and 10.0.0.0/24) connected by a router. The default gateway for the app server is 192.168.1.1, and for the DB server is 10.0.0.1. You have verified that the app server can ping the DB server by IP address successfully. However, the application fails to connect to the database. You have used telnet from the app server to test connectivity on port 3306 and it fails (connection refused). On the DB server, you check that the MySQL service is listening on 0.0.0.0:3306 and that the local firewall (firewalld) allows incoming connections on port 3306. What is the most likely cause of the connection failure?

Question 103mediummultiple choice

You administer a Linux server that acts as a network gateway. It has two network interfaces: eth0 (external, with IP 203.0.113.10/24, gateway 203.0.113.1) and eth1 (internal, with IP 192.168.1.1/24). The server is running firewalld and has IP forwarding enabled. Internal hosts (192.168.1.0/24) can access the internet through NAT, which is configured using firewalld's masquerade on the external zone. However, you need to allow a specific internal server (192.168.1.100) to be reachable from the internet on TCP port 443 (HTTPS). You add a port forwarding rule using firewall-cmd: 'firewall-cmd --zone=external --add-forward-port=port=443:proto=tcp:toport=443:toaddr=192.168.1.100'. After reloading the firewall, external users still cannot connect to 203.0.113.10:443. You verify that the internal server is running HTTPS and that its local firewall allows port 443. What is the most likely reason the port forwarding is not working?

Question 104hardmultiple choice

You are a senior Linux administrator for a large data center. A junior admin reports that a newly deployed application server (192.168.100.50/24, default gateway 192.168.100.1) cannot communicate with a legacy server (192.168.200.50/24, default gateway 192.168.200.1). The two subnets are connected via a router (192.168.100.1 and 192.168.200.1). From the app server, you can ping the legacy server's IP successfully. However, when you try to establish an SSH session from the app server to the legacy server, it times out. You check the legacy server's firewall (ufw) and find that it allows SSH (port 22) from the entire 192.168.0.0/16 range. You also confirm that the SSH daemon is running and listening on 0.0.0.0:22. What is the most likely cause?

Question 105mediummultiple choice

You manage a Linux server that provides DHCP services to a small office network using the dhcpd daemon. The server has two network interfaces: eth0 (192.168.1.1/24) serving the internal network, and eth1 (192.168.0.1/24) connected to a DMZ. The DHCP server is configured to serve addresses only on eth0. Users on the internal network report that they are not receiving IP addresses. You check the DHCP server and find that the dhcpd service is running and listening on UDP port 67. From a client, you run tcpdump and see DHCPDISCOVER packets being sent, but no DHCPOFFER from the server. You also verify that no firewall rules are blocking DHCP traffic on either side. What is the most likely reason for the failure?

Question 106easymulti select

An administrator is configuring a Linux server to act as a web server. The server has two network interfaces: eth0 (public IP 203.0.113.10) and eth1 (private IP 10.0.0.10). The default policy on the INPUT chain is DROP. The administrator wants to allow incoming HTTP (port 80) traffic from any source but only to the public interface. Which TWO iptables rules should be added?

Question 107mediummultiple choice

A system administrator is managing a RHEL 8 server that requires a static IP address on interface ens192. The administrator modifies /etc/sysconfig/network-scripts/ifcfg-ens192 to set BOOTPROTO=static, IPADDR=192.168.1.100, PREFIX=24, GATEWAY=192.168.1.1, and DNS1=8.8.8.8. After saving, the administrator runs 'systemctl restart NetworkManager'. The interface obtains the correct static IP and network connectivity works. However, after a reboot of the server, the interface fails to come up with the static IP and instead obtains an IP via DHCP from the local network. The administrator verifies that the DHCP server is active and that the physical connection is good. What is the most likely cause of the issue?

Question 108hardmultiple choice

A systems administrator is responsible for a production Linux server running CentOS 7 that provides SSH access to users. The administrator decides to tighten security by restricting SSH access to a specific management subnet 10.0.0.0/24. While connected to the server via SSH from a workstation on 10.0.0.50, the administrator adds the following iptables rule: iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/24 -j ACCEPT followed by iptables -P INPUT DROP. Immediately after the rule change, the administrator loses all connectivity to the server, including SSH. The administrator suspects that the new default policy dropped the existing SSH session. What is the most reliable method for the administrator to regain access to the server without rebooting?

Question 109mediummultiple choice

A Linux system administrator is troubleshooting a DNS resolution issue on a Ubuntu 20.04 server. The server is configured with a static IP address on interface eth0 via /etc/netplan/01-netcfg.yaml. The administrator set the DNS servers to 8.8.8.8 and 8.8.4.4 in the cloud-config file. After applying the netplan configuration, the server can resolve hostnames correctly. However, after a few days, users report that the server can no longer resolve external hostnames. The administrator checks /etc/resolv.conf and sees that it contains only a local DNS server (127.0.0.53) and no references to the public DNS servers. The administrator wants to ensure that the public DNS servers are always used and that local DNS is bypassed. What is the best course of action?

Question 110hardmultiple choice

An administrator is configuring network bonding on a RHEL 7 server with two physical NICs (eth0 and eth1) to provide redundancy. The bond interface bond0 is configured with mode 1 (active-backup). The administrator uses the following configuration in /etc/sysconfig/network-scripts/ifcfg-bond0: BONDING_OPTS="miimon=100 mode=1". The slave interfaces are configured with MASTER=bond0 and SLAVE=yes. After restarting the network service, the bond interface comes up with the active link on eth0. To test failover, the administrator disconnects the cable from eth0. The bond interface does not fail over to eth1. The administrator checks /proc/net/bonding/bond0 and sees that both slaves are listed but eth0 is still marked as active even though the cable is disconnected. What is the most likely reason for the failover failure?

Question 111mediummulti select

A system administrator needs to configure a network bond on a Linux server using NetworkManager. Which TWO steps are required to create a functional bond interface?

Question 112hardmultiple choice

Refer to the exhibit. A system administrator notices that SSH connections to the server are being dropped immediately. Assuming the server's external interface is eth0, which rule is responsible for this behavior?

Exhibit

# iptables -L -n -v --line-numbers
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination
1        0     0 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
2        0     0 ACCEPT     all  --  eth0   *       0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
3        0     0 DROP       all  --  eth0   *       0.0.0.0/0            0.0.0.0/0

Chain FORWARD (policy ACCEPT)
Chain OUTPUT (policy ACCEPT)

Question 113easymultiple choice