Networking

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?

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?

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?

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

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

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?

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?

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?

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?

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?

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?

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?

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?

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

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?

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?

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

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

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?

Match each Linux command to its function.

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?

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

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

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

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

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

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?

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?

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?

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?

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

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?

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

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?

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?

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?

Which bonding mode provides high availability without requiring switch configuration?

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?

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?

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?

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?

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

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

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?

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?

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

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

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?

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?

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?

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

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

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?

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

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

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?

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?

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?

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?

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?

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?

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

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?

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

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?

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?

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?

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

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.)

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

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

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

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?

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?

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

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?

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

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

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

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

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

A Linux server hosts a critical web application and is connected to the corporate network via a bonded interface bond0, combining eth0 and eth1 in active-backup mode. The server has a static IP 192.168.1.100/24 and default gateway 192.168.1.1. Recently, users report intermittent connectivity. The administrator runs 'ip link show' and sees that eth0 and eth1 are both state UP, but bond0 shows 'state UP' and 'NO-CARRIER'. The bond primary slave is eth0. Also, 'ping 192.168.1.1' fails. What should the administrator do next?

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

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

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

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?

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?

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

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?

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?

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?

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?

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

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.)

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

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

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

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

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

Match each systemd unit type to its purpose.

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

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

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

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?