LPIC-2 Network Client Management — 10 Questions

Question 1

A system administrator needs to configure a Linux client to use a specific DNS server for a particular domain. Which file should be modified to achieve this?

Accepted Answer

Edit /etc/resolv.conf. The /etc/resolv.conf file is the primary configuration file for DNS resolution on Linux systems. It allows specifying DNS servers (nameserver entries) and search domains, and can be configured to use a specific DNS server for a particular domain by adding a 'domain' or 'search' directive along with the appropriate nameserver. This file is read by the resolver library (glibc) during DNS lookups.

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Edit /etc/hosts

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Edit /etc/networks

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Edit /etc/nsswitch.conf

Question 2

A Linux client is unable to resolve hostnames for external domains but can ping internal hosts by IP. The /etc/resolv.conf file is correctly configured with a valid DNS server. What is the most likely cause?

Accepted Answer

The search domain in /etc/resolv.conf is incorrect, causing the resolver to append an inappropriate domain to queries.. When a search domain is incorrectly configured in /etc/resolv.conf, the resolver appends that domain to single-label hostnames before querying the DNS server. For external fully qualified domain names (FQDNs), this can cause the resolver to send queries like 'externaldomain.com.incorrect.domain' instead of the intended domain, leading to resolution failures. Since internal IPs are reachable (bypassing DNS) and the DNS server itself is valid, the issue is most likely the resolver's domain search behavior.

Answer

The /etc/hosts file contains an entry that overrides the DNS resolution for external domains.

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The nmblookup service is not running.

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The /etc/nsswitch.conf file is missing the 'dns' service in the 'hosts' line.

Question 3

An administrator needs to configure a Linux client to automatically obtain an IP address from a DHCP server but also ensure that the client uses a specific static DNS server (8.8.8.8) regardless of the DHCP-provided DNS. Which configuration should be applied?

Accepted Answer

Add 'supersede domain-name-servers 8.8.8.8;' to /etc/dhcp/dhclient.conf. The `supersede` directive in `/etc/dhcp/dhclient.conf` forces the DHCP client to replace any DNS server addresses received from the DHCP server with the specified value (8.8.8.8). This ensures the client uses the static DNS server regardless of what the DHCP server offers, while still obtaining its IP address dynamically.

Answer

Add 'append domain-name-servers 8.8.8.8;' to /etc/dhcp/dhclient.conf

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Edit /etc/sysconfig/network-scripts/ifcfg-eth0 and set PEERDNS=no and DNS1=8.8.8.8

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Add 'prepend domain-name-servers 8.8.8.8;' to /etc/dhcp/dhclient.conf

Question 4

A Linux client is experiencing slow name resolution. The /etc/nsswitch.conf file has the line 'hosts: files dns'. The /etc/hosts file contains many entries. What is the most effective way to improve resolution speed?

Accepted Answer

Change the nsswitch.conf line to 'hosts: dns files'. The current order 'hosts: files dns' causes the resolver to check the entire /etc/hosts file first for every query, which is slow when the file contains many entries. Reversing the order to 'hosts: dns files' makes the resolver query DNS first, which is typically faster for most lookups, and only falls back to the local file if DNS fails. This directly addresses the bottleneck without requiring additional services or data removal.

Answer

Increase the DNS timeout in /etc/resolv.conf

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Install and configure nscd (Name Service Cache Daemon)

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Remove all entries from /etc/hosts except localhost

Question 5

Which file is used by the NetworkManager daemon to store connection profiles on a Linux system?

Accepted Answer

/etc/NetworkManager/system-connections/. NetworkManager stores per-connection profiles in the `/etc/NetworkManager/system-connections/` directory. Each profile is a keyfile (`.nmconnection` file) containing connection parameters such as SSID, security settings, and IP configuration. When NetworkManager starts or a connection is modified, it reads and writes these files to persist network configurations across reboots.

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/etc/sysconfig/network-scripts/

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/etc/netctl/

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/etc/systemd/network/

Question 6

A Linux client is configured with two network interfaces: eth0 (connected to the internet) and eth1 (connected to a private LAN). The default route is set to eth0. The client can access the internet but cannot access hosts on the private LAN. What is the most likely cause?

Accepted Answer

There is no route to the private subnet via eth1.. Without a route to the private subnet via eth1, the client has no way to forward packets destined for the private LAN out of eth1. The default route via eth0 only handles traffic for destinations not explicitly matched by other routes; if the private subnet is not in the routing table, packets to that subnet will be sent to the default gateway (internet) and fail. The `ip route` command would show the missing entry, and adding a static route (e.g., `ip route add 192.168.1.0/24 dev eth1`) resolves the issue.

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A firewall on the client is blocking ICMP packets on eth1.

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The eth1 interface is not configured with an IP address.

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The eth1 interface is not receiving a DHCP lease.

Question 7

An administrator wants to ensure that a Linux client sends all DNS queries to a specific DNS server without relying on DHCP-provided DNS servers. Which configuration files should be modified?

Accepted Answer

Edit /etc/dhcp/dhclient.conf to add 'supersede domain-name-servers <desired IP>;'. The dhclient.conf file allows an administrator to override DHCP-provided DNS servers using the 'supersede' directive. This forces the DHCP client to ignore the DNS servers received from the DHCP server and instead use the manually specified DNS server when writing /etc/resolv.conf. This is a standard method for controlling DNS resolution on systems using dhclient.

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Configure NetworkManager to ignore DNS from DHCP and set the DNS manually in the connection profile

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Edit /etc/sysconfig/network-scripts/ifcfg-eth0 and set PEERDNS=no and DNS1=<desired IP>

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Edit /etc/resolv.conf and set the nameserver to the desired IP

Question 8

Which TWO commands can be used to display the current DNS resolver configuration on a Linux system? (Select TWO.)

Accepted Answer

nmcli dev show. The `nmcli dev show` command displays network device details managed by NetworkManager, including DNS configuration. The `resolvectl status` command shows the current DNS resolver state for systemd-resolved. These two commands provide the actual current resolver configuration. The `cat /etc/resolv.conf` file may be manually edited or dynamically generated and does not necessarily reflect the current resolver state on systems using systemd-resolved or NetworkManager.

Answer

dig localhost

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nslookup

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cat /etc/resolv.conf

Question 9

Which THREE conditions can cause a Linux DHCP client to fail to obtain an IP address? (Select THREE.)

Accepted Answer

A firewall on the client is blocking UDP port 67 (DHCP server).. A client-side firewall blocking UDP port 67 prevents the DHCP client from receiving DHCPOFFER and DHCPACK messages from the server. DHCP uses UDP ports 67 (server) and 68 (client); blocking port 67 on the client disrupts inbound server responses, causing the client to fail to obtain an IP address.

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The DHCP server is configured with a different subnet than the client's broadcast domain.

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The client interface is configured with a static IP address.

Question 10

Which TWO configuration files are commonly used to specify DNS resolver settings on a Linux system? (Select TWO.)

Accepted Answer

/etc/systemd/resolved.conf. /etc/systemd/resolved.conf is the configuration file for systemd-resolved, a service that manages DNS resolution on modern Linux systems. Option C is correct because /etc/resolv.conf is the traditional configuration file for specifying DNS resolver settings, including nameserver addresses and search domains, and is still widely used.

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/etc/nsswitch.conf

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/etc/dhcp/dhclient.conf

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/etc/hosts