Correct:

B. dnssec-keygen
Reasoning: dnssec-keygen is the standard and correct utility provided with BIND (and widely used for DNSSEC) to generate the cryptographic key pairs (both public and private keys) required for DNSSEC. These keys are used as Key Signing Keys (KSKs) and Zone Signing Keys (ZSKs) to sign DNS zones.
Incorrect:

A. Genkey-dnssec

Reasoning: This is not a standard or recognized command for generating DNSSEC keys.
C. Keygen-dnssec

Reasoning: While it contains the correct components, the order is incorrect for the standard command. The correct utility starts with dnssec-.
D. Dnssec-genkey

Reasoning: This is a plausible-sounding but incorrect name for the command. The correct utility uses keygen as the second part, not genkey.

Correct:

E. Provide a way to verify the association of X.509 certificates to DNS host names.
Reasoning: DANE (DNS-based Authentication of Named Entities) uses DNSSEC to bind X.509 certificates to domain names. By publishing TLSA (Transport Layer Security Authentication) records in DNSSEC-signed zones, DANE allows clients to cryptographically verify that the certificate presented by a server (e.g., a web server, mail server) is the legitimate certificate for that domain, preventing man-in-the-middle attacks where an attacker might present a fraudulent certificate issued by a compromised Certificate Authority (CA).
Incorrect:

A. Allow secure dynamic DNS updates.

Reasoning: Secure dynamic DNS updates are typically handled by TSIG (Transaction Signature) records, which use shared secrets to authenticate updates to DNS zones. While DANE uses DNSSEC, its primary purpose is not dynamic updates.
B. Discover which servers within a DNS domain offer a specific service.

Reasoning: Discovering services within a DNS domain is the purpose of SRV (Service) records (e.g., _sip._tcp.example.com). DANE is about authenticating the certificate used by those services, not discovering them.
C. Verify the integrity of name information retrieved via DNS.

Reasoning: While DANE relies on DNSSEC, “verifying the integrity of name information retrieved via DNS“ is the broader purpose of DNSSEC itself. DANE specifically extends this by adding a layer of trust for X.509 certificates, building on DNSSEC‘s integrity verification, but it‘s not the sole purpose.
D. Invalidate name information stored on caching name servers to speed up DNS updates.

Reasoning: Invalidating cached information to speed up updates is usually done by adjusting TTL (Time To Live) values in DNS records or by explicitly flushing caches. DANE does not perform this function. DNSSEC (which DANE relies on) can actually introduce a slight overhead due to cryptographic validation, not speed up updates.

Correct:

B. A forward-only configuration is often faster than a complete recursive configuration.
Reasoning: In a forward-only configuration, the local DNS server immediately sends all non-local queries to a designated upstream forwarder (usually the ISP‘s DNS server or a well-known public DNS server like Google‘s 8.8.8.8). This means the local server doesn‘t have to perform iterative queries starting from the root servers. It offloads the entire recursive process to the forwarder, which often has a large cache and is optimized for recursive lookups. For a local network, this can result in faster resolution times, as the local server doesn‘t need to traverse the entire DNS hierarchy for every new query.
Incorrect:

A. A forward-only configuration will work even if the ISP‘s DNS server does not respond.

Reasoning: This is incorrect. If the ISP‘s DNS server (the configured forwarder) does not respond, a forward-only server will fail to resolve external queries. Its entire external resolution capability relies on the forwarder. A full recursive server, on the other hand, would then attempt to contact root servers and perform iterative lookups if its initial configured hints didn‘t respond.
C. A forward-only configuration can cache DNS data for local access.

Reasoning: This statement is true in isolation (a forward-only server does cache DNS data for local access), but it‘s not an advantage over a full recursive lookup configuration. A full recursive server also caches DNS data for local access. Both types of caching DNS servers aim to improve performance by storing previously resolved queries.
D. A routing-only configuration eliminates the need for an ISP.

Reasoning: “Routing-only configuration“ is not a standard term in DNS. Regardless, no DNS configuration, whether forward-only or recursive, eliminates the need for an ISP if you want to access the public internet. An ISP provides the network connectivity to reach other DNS servers and the internet as a whole.

Correct:

C. kill -s SIGHUP 2798
Reasoning: Many daemon processes, including BIND (named), are programmed to reload their configuration files when they receive a SIGHUP (Signal Hang Up) signal. This is a graceful way to apply new configuration changes without stopping and restarting the entire service, which would cause a temporary disruption. kill -s SIGHUP explicitly sends this signal.
Incorrect:

A. kill -9 2798

Reasoning: kill -9 sends the SIGKILL signal, which is a non-catchable, non-ignorable signal that immediately terminates the process. This is a “last resort“ kill that does not allow the process to perform any cleanup or graceful actions, including reloading its configuration. Using kill -9 on named would abruptly stop it, potentially leading to issues, and it would definitely not reload the configuration.
B. kill 2798

Reasoning: When no signal is specified with the kill command, it defaults to sending SIGTERM (Signal Terminate). While SIGTERM is a polite request for a process to terminate gracefully, it does not typically instruct processes like named to reload their configuration. It tells them to shut down.
D. kill -s SIGTERM 2798

Reasoning: As explained for option B, SIGTERM is a signal for graceful termination. While the process can catch and handle it (e.g., to clean up before exiting), its standard behavior for named is to shut down, not to reload its configuration.

Correct:

B. fileinto

Reasoning: The fileinto action is a core Sieve action used to deliver a message to a specific mailbox or folder. For example, fileinto “Junk“; would move the email into a “Junk“ folder. This is a very common use case for Sieve for organizing incoming mail.
D. discard

Reasoning: The discard action is a core Sieve action that silently discards the message without any notification to the sender or recipient. It essentially deletes the message immediately. This is useful for filtering out spam or unwanted emails without bouncing them.
E. reject

Reasoning: The reject action is a core Sieve action that rejects the message and typically sends a delivery status notification (DSN) to the sender, explaining why the message was rejected. This is often used for blocking messages that fail certain criteria and informing the sender.
Incorrect:

A. drop

Reasoning: While “drop“ is a common term in networking and filtering to mean discard, drop is not a standard Sieve core action. The equivalent core Sieve action is discard.
C. relay

Reasoning: The relay action is not a standard Sieve core action. Sieve is primarily concerned with local mail delivery and filtering after the mail has been received by the Mail Delivery Agent (MDA). Relaying mail (forwarding it to another SMTP server) is typically a function of the Mail Transfer Agent (MTA) before it reaches the MDA or through a separate redirect Sieve action (which is an extension, not core).

Correct:

D. ~/.ssh/id_rsa.pub

Reasoning: This file is created and contains the public key part of the RSA key pair. This is the key you would typically copy to remote servers (e.g., into ~/.ssh/authorized_keys) to allow passwordless authentication from your machine. It‘s meant to be shared.
E. ~/.ssh/id_rsa

Reasoning: This file is created and contains the private key part of the RSA key pair. This file must be kept secret and secure on your local machine, as it‘s used to authenticate you to remote servers. It‘s often protected with a passphrase during generation.
Incorrect:

A. ~/.ssh/id_rsa.prv

Reasoning: The .prv extension is not the standard or default extension for SSH private key files generated by ssh-keygen. The private key file itself is typically named id_rsa (or id_dsa, id_ecdsa, id_ed25519 depending on the algorithm).
B. ~/.ssh/id_rsa.key

Reasoning: The .key extension is not the standard or default extension for SSH public or private key files. While some other cryptographic systems might use .key, ssh-keygen uses .pub for the public key and no extension for the private key by default.
C. ~/.ssh/id_rsa.crt

Reasoning: The .crt extension typically indicates a certificate, often in X.509 format, which is used in SSL/TLS. While SSH can use certificates (SSH certificates), ssh-keygen by default generates raw public/private key pairs, not X.509 certificates.
The question specifies “accepting the default values,“ and default ssh-keygen behavior does not create a .crt file.

Correct:

C. named.conf
Reasoning: This is the standard and correct name for the main configuration file for the BIND (Berkeley Internet Name Domain) DNS server on Linux systems. BIND‘s daemon is named named, and its configuration file reflects that name. It‘s where global options, zone definitions, access control lists, and other server-wide settings are configured.
Incorrect:

A. bind.cf

Reasoning: This is not a standard or correct name for the BIND configuration file. The .cf extension is sometimes used for configuration files, but bind.cf is not used by BIND.
B. named.cf

Reasoning: While it includes named, the correct extension for the BIND configuration file is .conf, not .cf.
D. bind.conf

Reasoning: While it uses the bind name and .conf extension, the official and widely adopted name for the main BIND configuration file is named.conf.

Correct:

A. ldappasswd
Reasoning: ldappasswd is the dedicated command-line utility specifically designed to change a user‘s password in an OpenLDAP (or any LDAP-compliant) directory. It interacts with the LDAP server using the LDAP protocol to perform the password modification operation.
Incorrect:

B. olppasswd

Reasoning: This is not a standard or recognized command for changing passwords in OpenLDAP. The prefix olp (OpenLDAP) is not used in this manner for client tools.
C. ldapchpw

Reasoning: While chpw is sometimes used in password-changing commands (like chpasswd), ldapchpw is not a standard OpenLDAP utility. The correct command is ldappasswd.
D. ldpasswd

Reasoning: Similar to ldapchpw, this is not a standard or recognized command in the OpenLDAP toolset for password changes.
E. setent

Reasoning: setent is not an OpenLDAP command. It sounds like a generic command for “setting entries,“ but it‘s not part of the standard OpenLDAP client utilities for password management.

Correct:

D. Your ISP‘s DNS server is reliable, but slow.
A caching DNS server‘s primary benefit is to improve DNS query performance by storing the results of previous queries. If your ISP‘s DNS server is reliable (meaning it gives correct answers) but slow, a local caching DNS server will store these answers after the first query. Subsequent queries for the same domain name will then be served directly from the local cache, providing much faster responses to clients on your network, without needing to go to the slow ISP server again.
Incorrect:

A. You need to manage the hostnames for 150 computers.

Managing hostnames for 150 computers requires an authoritative DNS server (one that holds the zone files for your domain) or a DHCP server integrated with DNS. A caching-only DNS server does not store authoritative zone information; it only caches responses from other servers.
B. You need to provide a second DNS server for your domain.

Providing a second DNS server for your domain means setting up a secondary (slave) authoritative DNS server that receives zone transfers from your primary. A caching DNS server does not serve as an authoritative source for your own domain‘s records.
C. Your entire network connection often goes down.

If your entire network connection goes down, a caching DNS server will be of limited help for new queries. While it can serve answers from its cache for domains it has already resolved, it cannot resolve new domains or refresh expired entries if there‘s no connectivity to external DNS servers. The fundamental problem is the lack of network access, not DNS speed.

Correct:

A. The DNS server caches will be cleared.
Reasoning: The rndc command is the remote name daemon control utility, used to administer a running BIND DNS server. The flush command specifically instructs named (the BIND daemon) to clear its DNS caches (both the regular cache and the negative cache). This is often done when troubleshooting DNS issues, or when a change to a zone has been made on an authoritative server and you want to ensure resolvers pick up the new information quickly without waiting for TTLs to expire.
Incorrect:

B. All zone files on the DNS server will be emptied.

Reasoning: The rndc flush command only affects the in-memory cache of the DNS server. It does not modify, empty, or delete any of the actual DNS zone files stored on disk (e.g., in /var/named). Zone files are the authoritative source of data, and flushing the cache just means the server will have to look up that data again the next time it‘s requested.
C. The DNS server computer will be restarted.

Reasoning: rndc flush is a command sent to the named process itself. It causes a specific internal action (cache clearing) within the named daemon. It has no effect on the operating system or the computer‘s power state; it will not restart the entire machine.
D. DNS server program will be restarted.

Reasoning: While rndc can be used to restart the named program (e.g., rndc reload or rndc restart), the flush subcommand specifically clears the cache. It does not cause a full restart of the named process. A restart would clear the cache as a side effect, but flush achieves only the cache clearing without the downtime of a restart.

Correct:

A. sender_canonical_maps
Reasoning: In Postfix, the sender_canonical_maps parameter is specifically used to rewrite sender addresses as mail leaves or enters the system. It maps original sender addresses to new, canonical (standardized or preferred) sender addresses. This transformation occurs before other address rewriting stages and explicitly targets only the sender.
Incorrect:

B. sender_rewrite_maps

Reasoning: This is not a standard or valid Postfix configuration parameter. Postfix uses canonical_maps, sender_canonical_maps, and recipient_canonical_maps for various types of address rewriting, but not sender_rewrite_maps.
C. alias_maps

Reasoning: The alias_maps parameter in Postfix is used for local recipient aliasing. It maps a recipient address (e.g., webmaster or postmaster) to one or more local users, files, or programs. It deals with recipients and local delivery, not outbound sender address modification.
D. alias_rewrite_maps

Reasoning: This is not a standard or valid Postfix configuration parameter. Similar to sender_rewrite_maps, it does not exist in Postfix‘s official documentation for address rewriting.

Correct:

A. If BIND is malfunctioning or compromised, it is less likely to damage other parts of the computer.
Reasoning: This is the primary security advantage of running any service within a chroot jail (or “prison“). A chroot environment effectively changes the apparent root directory (/) for the running process. This means that even if a vulnerability in BIND were exploited, the attacker‘s access would be confined to the chroot jail‘s directory structure. They would not be able to access or modify files outside of that confined environment on the rest of the file system, significantly limiting the potential damage or scope of compromise.
Incorrect:

B. The server refuses to transfer full zone files, except for slaves in a short list.

Reasoning: Restricting zone transfers to a specific list of slave servers is controlled by the allow-transfer directive within the BIND named.conf configuration file, specifically in zone blocks. It has nothing to do with running BIND in a chroot jail. A chroot environment affects file system access, not network transfer policies.
C. BIND encrypts data transfers to and from all of its customers.

Reasoning: BIND, by default, uses standard DNS protocols which are unencrypted. Encryption of DNS traffic (e.g., DNS over TLS/HTTPS) requires additional configuration or a different protocol entirely, and it is not a feature provided by running BIND in a chroot jail. A chroot confines file system access, it doesn‘t encrypt network traffic.
D. BIND can authenticate itself to other servers, reducing the chances of cache poisoning.

Reasoning: BIND can authenticate itself to other servers, and this is crucial for preventing cache poisoning (e.g., through DNSSEC or TSIG keys for zone transfers/updates). However, this authentication capability is a feature of BIND‘s DNS protocol implementation and DNSSEC, not a result of running it in a chroot jail. A chroot environment provides file system isolation, not cryptographic authentication mechanisms for network communication.

Correct:

A. passwd

Reasoning: The passwd backend allows OpenLDAP to authenticate users against the local system‘s passwd (and shadow) file. While it‘s primarily for authentication and often used for simple scenarios or when migrating, it acts as a valid backend for user information.
D. ldap

Reasoning: The ldap backend (often referred to as meta backend in older contexts, but ldap is the current, more specific name) is used to proxy or refer queries to another LDAP server. This is crucial for building distributed LDAP directories where a local slapd instance acts as a front-end to a remote LDAP directory. It allows you to integrate data from other LDAP servers seamlessly.
E. bdb

Reasoning: bdb (Berkeley DB) was a very common and traditional backend for OpenLDAP. It stores LDAP data directly in Berkeley DB files on the local filesystem. While newer versions often default to hdb (Hierarchical Database, which is an optimized variant of bdb), bdb is still a recognized and configurable backend type.
Incorrect:

B. xml

Reasoning: OpenLDAP does not have a built-in xml backend for storing directory data directly in XML files. While LDAP data can be represented in LDIF (LDAP Data Interchange Format), which is text-based, and tools can export/import to/from XML, XML itself is not a native backend storage type for slapd.
C. text

Reasoning: There is no generic text backend in OpenLDAP. Directory data is stored in structured databases (like bdb, hdb, mdb) or accessed from other services (like ldap, passwd, shell).
Common OpenLDAP Backends (for LPIC-2 context):
The most commonly encountered and supported backends you should be familiar with are:

hdb: Hierarchical Database (currently the recommended and default for new installations, an improved version of bdb).
mdb: Memory-Mapped Database (a newer, high-performance option).
bdb: Berkeley DB (older, but still widely deployed).
ldap / meta: Proxying to another LDAP server.
monitor: For monitoring the slapd server itself.
null: A discard backend.
passwd: For passwd file authentication.
shell: For using external shell scripts.

Correct:

C. options
Reasoning: The directory statement, which specifies the default location where BIND (named) should look for zone files, is typically defined within the options block of the named.conf file. For example:
options {
directory “/var/named“;
// other options
};

This sets a base path for unqualified zone file names in zone statements.

Incorrect:

A. include

Reasoning: The include directive is used to include other configuration files into named.conf. It doesn‘t define the zone file directory itself, but it might point to a file that contains zone or options statements.
B. zones

Reasoning: While individual zone statements define each DNS zone, they specify the name of the zone file relative to the directory defined in the options section (or an absolute path). The zones section itself does not define the default directory for all zone files.
D. files

Reasoning: There is no standard top-level section or directive called files in named.conf that defines the zone file directory.

Correct:

D. type hint;
Reasoning: In BIND‘s named.conf configuration, a zone block with type hint; specifies a caching-only zone. This type of zone is used to define the root name servers (often found in a named.ca file). The server doesn‘t have any authoritative data for the zone itself; instead, it uses the hints to find the root servers and then performs recursive lookups, caching the results for future queries. This effectively makes the server a caching-only DNS server for that zone, relying entirely on upstream servers for answers.
Incorrect:

A. type cache;

Reasoning: While the server performs caching, type cache; is not a valid or standard zone type directive in BIND for defining a caching-only zone. The correct type is hint.
B. type mime;

Reasoning: type mime; is not a valid or standard zone type directive in BIND. MIME (Multipurpose Internet Mail Extensions) is related to email content types, not DNS zone definitions.
C. type root;

Reasoning: While the concept of “root“ servers is central to DNS, type root; is not a valid zone type directive in BIND for defining a caching-only zone. The correct type for the root hints zone (which enables caching behavior) is hint.

Correct:

C. Servers using TSIG must be in sync (time zone!).

Reasoning: TSIG (Transaction Signature) uses timestamps as part of its cryptographic signature process to prevent replay attacks. For the signature to be valid, the time on the client (e.g., a DHCP server performing an update) and the server (the DNS server receiving the update) must be closely synchronized. A significant time difference between the two can cause the TSIG signature to be deemed invalid, leading to update failures. While the time zone itself isn‘t the issue, the absolute time of the machines needs to be in sync. The parenthetical “time zone!“ in the option is a common hint to emphasize that precise time synchronization is critical.
E. TSIG is used only in the server configuration.

Reasoning: TSIG keys and their associated settings (like the algorithm and key name) are defined within the named.conf file (the server configuration) on both the DNS server and the client (e.g., another DNS server for zone transfers, or a DHCP server for dynamic updates). These keys are referenced in the zone and allow-update directives, but the key material itself and its definition are part of the server‘s overall configuration, not directly embedded within the zone data itself.
Incorrect:

A. TSIG is used in zone files.

Reasoning: TSIG keys are not defined or stored directly within DNS zone files. Zone files contain resource records (like A, MX, NS, SOA). TSIG keys are cryptographic secrets defined in the BIND named.conf file or an included file, and then referenced in specific controls or key statements, or within zone blocks for update permissions.
B. TSIG is a signal to initiate a zone update.

Reasoning: TSIG is a method of authentication for DNS messages, including zone updates. It‘s not a “signal“ to initiate an update. The update itself is initiated by a client (e.g., a DHCP server). TSIG ensures that the initiated update request is legitimate and comes from an authorized source.
D. TSIG is used for encrypting zone data.

Reasoning: TSIG provides authentication and integrity for DNS messages, meaning it verifies who sent the message and that it hasn‘t been tampered with. It does not provide encryption for the zone data or the DNS messages themselves. The content of DNS messages secured by TSIG is still sent in plain text.

Correct:

A. An A record for dns1.imbrium.luna.edu.
Reasoning: When an NS (Name Server) record delegates authority for a subdomain (like imbrium.luna.edu.) to a name server whose own hostname (dns1.imbrium.luna.edu.) is within that same delegated subdomain, this creates what is known as a glue record. For the NS record to be resolvable and for clients to be able to find dns1.imbrium.luna.edu., its IP address (an A record for IPv4 or AAAA for IPv6) must be provided within the parent zone file (luna.edu.). Without this “glue,“ a resolver trying to find imbrium.luna.edu. would get an NS record pointing to dns1.imbrium.luna.edu., but then it wouldn‘t know how to resolve dns1.imbrium.luna.edu. itself without an IP address, leading to a circular dependency.
Incorrect:

B. A CNAME record for dns1.imbrium.luna.edu.

Reasoning: A CNAME (Canonical Name) record is an alias. While CNAME records are valid for hostnames, you cannot use a CNAME record for a name server that is the target of an NS record. An NS record must point to a canonical name, not an alias. More importantly, it doesn‘t provide the necessary IP address for glue.
C. An MX record for imbrium.luna.edu.

Reasoning: An MX (Mail Exchanger) record specifies the mail server(s) responsible for handling email for a domain. While imbrium.luna.edu. might have an MX record, it‘s completely unrelated to the validity of the NS record or the necessity of providing glue for the name server‘s hostname.
D. A PTR record for imbium.luna.edu.

Reasoning: A PTR (Pointer) record is used for reverse DNS lookups (mapping an IP address back to a hostname). PTR records are placed in reverse lookup zones (e.g., in-addr.arpa or ip6.arpa). The question is about a forward lookup zone (luna.edu.) and the validity of an NS record for delegation, not reverse lookups.

Correct:

C. domain-name-servers
Reasoning: In the ISC DHCP server (DHCPD) configuration file (dhcpd.conf), the domain-name-servers option is the standard directive used to specify the IP address(es) of the DNS servers that should be provided to DHCP clients. Clients will then use these addresses for name resolution. It can be used globally, per shared-network, or per pool/host.
Incorrect:

A. name-server

Reasoning: This is not a standard or valid option in the ISC DHCPD configuration for defining DNS servers.
B. servers

Reasoning: While conceptually related to servers, servers is not the specific directive used in dhcpd.conf for DNS servers. Other options might use a servers keyword (e.g., ntp-servers), but not for DNS.
D. domain-server

Reasoning: This is not a standard or valid option in the ISC DHCPD configuration for defining DNS servers. The correct option uses domain-name-servers.

Correct:

D. The DNS server operates in an environment isolated from the rest of the system.
Reasoning: A “chroot jail“ or “chroot prison“ (often colloquially referred to as a “DNS Cage“ when applied to a DNS server like BIND) is a security mechanism. It changes the apparent root directory (/) for a running process and its children. This isolates the process (in this case, the DNS server) to a specific directory subtree. If the DNS server were compromised, an attacker would theoretically be confined within this chroot environment and would not be able to access or modify files and directories outside of the jailed area on the rest of the host system. This significantly limits the potential damage from a successful exploit.
Incorrect:

A. The DNS server is on a remote machine.

Reasoning: Running a DNS server in a chroot jail is a local security measure applied to the same machine where the server is running. It has nothing to do with whether the server is located remotely or locally in a network sense.
B. The DNS server identifies the attacker and informs the police.

Reasoning: While DNS servers can log activity, and those logs might be used in forensics to identify attackers, a chroot jail itself does not perform attacker identification or notify law enforcement. Its purpose is isolation, not active threat detection or reporting.
C. The DNS server is inaccessible.

Reasoning: If a DNS server were “inaccessible,“ it wouldn‘t be able to perform its function. A chroot jail isolates the file system access of the server process, but it does not prevent network accessibility to its configured ports (e.g., TCP/UDP port 53) from legitimate clients. If it were inaccessible, it would be useless.

Correct:

B. It is a master or slave that allows zone transfers to two other computers.
Reasoning: The allow-transfer { … }; directive in named.conf specifies which IP addresses are permitted to request zone transfers from the server where this configuration is applied.
If this server is a master for a zone, it means 10.23.98.102 and 10.202.79.121 are explicitly allowed to pull the zone data from it (acting as slaves).
If this server is a slave for a zone, the allow-transfer directive would dictate which other servers (potentially its own slaves further down the hierarchy) are allowed to pull the zone from it. In this scenario, it‘s acting as a source of zone data for other servers, not as a recipient of zone data.
Therefore, the presence of allow-transfer means this server provides zone transfers to the listed IPs, regardless of whether it‘s a primary (master) or secondary (slave) server itself for that particular zone.
Incorrect:

A. It is a slave that transfers data from two other computers.

Reasoning: The allow-transfer directive controls outbound transfers (who can pull from this server). To transfer data from another computer (to be a slave), the zone definition would include a masters directive, like masters { 10.23.98.102; 10.202.79.121; };.
C. It is a slave that transfers data to two other computers.

Reasoning: While it could be a slave and transfer data to two other computers, the phrasing “transfers data to“ implies it‘s actively pushing data. DNS zone transfers are typically pulled by the slave from the master. The allow-transfer directive permits these pulls. The critical part of this option that makes it less accurate than B is that it only considers the “slave“ role and doesn‘t fully capture the outbound nature of allow-transfer. However, if it‘s a slave, it can indeed be a source for other downstream slaves. The primary strength of option B is its explicit “allows zone transfers to“ which precisely describes allow-transfer.
D. It is a master that transfers data over two Ethernet interfaces.

Reasoning: allow-transfer specifies allowed IP addresses, not network interfaces. While those IP addresses might be associated with different interfaces, the directive itself doesn‘t directly configure interfaces or indicate the number of interfaces used for transfer. It‘s solely about access control for zone transfers.

Correct:

C. Add an A record for mailhost at fred‘s IP address.
Reasoning: An MX (Mail Exchanger) record must always point to a hostname, not directly to an IP address. For email to be directed to fred, the mailhost.example.org MX record needs to resolve to an IP address. Since mailhost.example.org is the existing MX record‘s target, and you want fred to be the actual mail server, you should ensure that mailhost.example.org resolves to fred‘s IP address. The most direct way to do this is to create an A record (for IPv4) or AAAA record (for IPv6) for mailhost.example.org that points to fred‘s IP address. This effectively makes mailhost.example.org an alias for fred‘s IP for the purpose of receiving mail.
Incorrect:

A. Add a CNAME record for mailhost to fred.

Reasoning: While CNAME records can create aliases, a CNAME record cannot coexist with other records (like an MX record) for the same name at the same level. If mailhost.example.org already has an MX record, adding a CNAME for mailhost would create a conflict and is generally considered bad practice or invalid for names that have other resource records. The standard approach is to have an A record directly for the name pointed to by the MX record.
B. Add another MX record pointing to fred‘s IP address.

Reasoning: As mentioned, MX records must point to hostnames, not directly to IP addresses. Even if it were syntactically allowed, you don‘t add an MX record pointing to an IP. You point it to a hostname, and that hostname then resolves to an IP address via an A or AAAA record.
D. Add a PTR record from mailhost to fred.

Reasoning: A PTR (Pointer) record is used for reverse DNS resolution (mapping an IP address back to a hostname). It has no direct bearing on how incoming email is directed by an MX record or how mailhost.example.org resolves to an IP address for receiving mail. While good reverse DNS is important for email delivery (anti-spam checks), it‘s not the mechanism to direct mail to a specific server.

Correct:

B. linus IN A 192.168.17.198
Reasoning: You want to map the hostname linus.example.com to the IPv4 address 192.168.17.198. An A record (Address record) is precisely what performs this mapping for IPv4. The format is hostname IN A IPv4_address. In the example.com zone file, linus is the hostname relative to example.com, IN indicates “Internet“, A is the record type, and 192.168.17.198 is the IPv4 address.
Incorrect:

A. 198 IN PTR linus.example.com.

Reasoning: This is a PTR (Pointer) record, which is used for reverse DNS resolution (mapping an IP address back to a hostname). PTR records belong in a reverse lookup zone file (e.g., 17.168.192.in-addr.arpa), not in the forward lookup zone file for example.com. While you would typically create a corresponding PTR record in the reverse zone, this option does not achieve the goal of allowing users to access linus.example.com via its IP.
C. 198 IN TXT linus.example.com.

Reasoning: A TXT (Text) record is used to hold arbitrary text strings. While TXT records are used for various purposes (e.g., SPF, DKIM, DMARC for email authentication), they do not map a hostname to an IP address for general access. The 198 would also typically be a hostname or relative name, not just an IP octet in a forward zone.
D. linus IN MX 192.168.17.198

Reasoning: An MX (Mail Exchanger) record specifies the mail server(s) responsible for handling email for a domain. It tells other mail servers where to send email for linus.example.com. More importantly, MX records must point to a hostname, not directly to an IP address. Therefore, this line is incorrect both in its purpose and its format (pointing to an IP).

Correct:

C. Cryptographic authentication of DNS zones.
Reasoning: DNSSEC (Domain Name System Security Extensions) provides a way to cryptographically sign DNS data within zones. This signing allows DNS resolvers to verify the authenticity and integrity of DNS responses. It ensures that the DNS data they receive (like IP addresses for a domain) is the same data published by the zone owner and has not been tampered with in transit. It specifically uses digital signatures to authenticate the origin of DNS records and to prove that the records have not been altered.
Incorrect:

A. Consult a secure DNS section.

Reasoning: While DNSSEC enables secure DNS consultations, this option is too vague and doesn‘t explain how DNSSEC achieves security. It‘s a consequence, not the core function.
B. Define a secure DNS section.

Reasoning: DNSSEC doesn‘t “define“ a section; it adds security features (like RRSIG, DNSKEY, NSEC records) to existing DNS zones to make them cryptographically secure. The secure elements are part of the zone, not a separate “secure section.“
D. Secondary DNS queries for local zones.

Reasoning: DNSSEC is about securing the integrity and authenticity of DNS data regardless of whether it‘s a primary or secondary query, or a local or remote zone. It‘s not limited to secondary queries or local zones.
E. Encrypted DNS queries between nameservers.

Reasoning: DNSSEC provides authentication and integrity, but it does not provide encryption for DNS queries or responses. DNS traffic, even with DNSSEC, is typically unencrypted. For encryption, separate protocols like DNS over TLS (DoT) or DNS over HTTPS (DoH) are used.

Correct:

C. mail_location
In Dovecot, mail_location is the primary and most important configuration variable for defining where user mailboxes are stored on the filesystem. It supports various formats (like mbox, maildir, mdbox, sdbox) and can include variables to specify paths relative to user homes, such as mail_location = maildir:~/Maildir.
Incorrect:

A. mbox

mbox is a mailbox format (a single file containing all messages for a user), not a configuration variable that defines the location. While mail_location can be set to use the mbox format (e.g., mail_location = mbox:~/mail), mbox itself is not the variable specifying the location.
B. user_dir

user_dir is not a standard Dovecot configuration variable for mail location. While there might be variables related to user directories in other contexts, mail_location is specific to mail storage.
D. user_mail_dir

Similar to user_dir, user_mail_dir is not a standard Dovecot configuration variable. It‘s a plausible-sounding name but incorrect.
E. maildir

maildir is another common mailbox format (a directory structure where each message is a separate file). Like mbox, it‘s a format that can be specified within the mail_location variable (e.g., mail_location = maildir:~/Maildir), but it is not the variable itself that defines the location.

Correct:

E. ip6tables
This is the dedicated command-line utility used to administer IPv6 packet filtering rules (netfilter rules) on Linux. It functions analogously to iptables for IPv4, but operates on the IPv6 protocol stack.
Incorrect:

A. iptables6

This is not the correct command name. While it clearly indicates IPv6, the standard utility is ip6tables.
B. iptablesv6

This is also not the correct command name. Again, it implies IPv6, but the actual command is ip6tables.
C. ipv6tables

Similar to the above, this is a plausible but incorrect command name. The convention used in Linux is ip6tables.
D. iptables

This command is specifically for administering IPv4 netfilter rules. While it‘s part of the same netfilter framework, it cannot be used directly for IPv6 rules. You must use ip6tables for IPv6.

Correct:

C. Nslookup
Nslookup (Name Server Lookup) provides an interactive mode when invoked without arguments or with a specific server. In interactive mode, you can repeatedly enter domain names, record types (e.g., A, MX, NS), and even change the DNS server being queried without re-running the command. This makes it an interactive tool for exploring DNS information.
Incorrect:

A. host

The host command is a simple utility for performing quick DNS lookups. While useful, it is primarily designed for single, non-interactive queries. You run host example.com and it provides an answer, then exits. It does not offer a persistent interactive shell like nslookup or dig.
B. Named

Named is the actual daemon (program) that implements the BIND DNS server. It is a background service that answers DNS queries, not a client-side command-line tool for performing lookups.
D. dig

dig (domain information groper) is a powerful and flexible command-line tool for performing DNS lookups. While it provides very detailed output and supports many query options, its primary mode of operation is typically non-interactive, similar to host. You provide all arguments on the command line, and it executes the query and exits. While it can be scripted for multiple queries, it doesn‘t offer a built-in interactive prompt for entering multiple queries sequentially without restarting the command, like nslookup does natively.

Correct:

D. Invoke named with “named -t / var / named / root -u nobody“
Reasoning: This is the most direct and correct way to launch named (the BIND DNS server daemon) within a chroot environment and with a specific user and group.
-t /var/named/root: The -t (or –chroot) option tells named to chroot into the specified directory (/var/named/root in this case) immediately after parsing its command-line arguments. This makes /var/named/root appear as the root directory (/) to the named process, confining its file system access.
-u nobody: The -u (or –user) option tells named to drop its root privileges and switch to the specified user (nobody in this case) after initial setup. This significantly increases security by reducing the privileges of the running daemon. (Note: BIND also has a -g or –group option for setting the group, but often nobody is part of the nogroup group, or the user‘s primary group is used if -g isn‘t specified). The question asks for “nogroup user and group,“ and nobody is often associated with nogroup.
Incorrect:

A. Add “user nobody; group nogroup; chroot / var / named / root“ to named.conf

Reasoning: While BIND configuration does have user and group directives to specify the user/group to run as, and directory for setting the working directory, there is no chroot directive directly in named.conf for setting up the chroot jail. The chroot environment itself is usually set up by the command-line options (-t) or by the init/systemd script that starts named.
B. Use /usr/bin/chroot after running “chown nobody.nogroup named“

Reasoning: While /usr/bin/chroot can be used to manually enter a chroot environment, it‘s not the standard way to launch named persistently for a service. More importantly, simply running chown nobody.nogroup named only changes the ownership of the named executable, not its runtime user, nor does it inherently put it in a chroot jail. The named daemon itself has built-in chroot capabilities for convenience and robustness.
C. Named runs as nobody / nogroup by default, so just call it as “name –chroot / var / named / root“

Reasoning:
named does not run as nobody/nogroup by default if started as root. It typically runs as root initially to bind to privileged ports (like 53) and then drops privileges to a less privileged user (often named or bind) and group (often named or bind). It does not default to nobody/nogroup.
The command name –chroot /var/named/root is also missing the -t or –chroot flag for named. While –chroot is an alias for -t, using name instead of named is a typo.
Even if the command was correct, the premise that it runs as nobody/nogroup by default is false.

Correct:

C. root
The root directive in Nginx specifies the document root for a request. This is the absolute path to the directory from which Nginx will serve files. It can be defined within http, server, or location blocks, with the most specific root directive taking precedence. For example, root /var/www/html; tells Nginx to look for requested files under /var/www/html.
Incorrect:

A. DocumentRoot

DocumentRoot is the equivalent directive used in Apache HTTPD to define the web server‘s document root. While it serves the same purpose, it is not a valid Nginx directive.
B. htdocs

htdocs is a common name for a directory that serves as a web server‘s document root (e.g., in Apache installations or XAMPP/WAMP stacks). It is a convention, not an Nginx configuration directive itself.
D. base_dir

This is not a standard Nginx directive for defining the document root. Nginx uses root.
E. location

The location directive defines how Nginx handles requests for specific URIs or URL patterns. While a root directive is often placed within a location block to define the document root for that specific location, location itself does not define the file system path for content retrieval. It defines the context in which root (or proxy_pass, etc.) will operate.

Correct:

B. PermitRootLogin yes

Reasoning: Allowing direct root login via SSH is a significant security risk. If an attacker manages to guess or crack the root password, they gain immediate, full control of the system. Best practice is to disable direct root login (PermitRootLogin no or PermitRootLogin prohibit-password) and instead require users to log in with a regular user account, then use sudo or su to gain root privileges. This provides an audit trail and an extra layer of protection.
C. PermitEmptyPasswords no

Reasoning: Allowing users to authenticate with empty passwords (PermitEmptyPasswords yes) is an extremely severe security vulnerability. It means anyone who knows a valid username but no password can log in. This should always be set to no to enforce proper password security.
Incorrect:

A. Port 22

Reasoning: Port 22 is the standard, default port for SSH. While changing the default port (Port 2222, for example) can reduce the amount of automated scanning/brute-force attempts against the default port, it is not a fundamental security hardening measure. It‘s security through obscurity, as a determined attacker will simply scan all ports. Disabling root login and enforcing strong passwords are far more important for security than changing the port. Thus, changing Port 22 is not a necessary change to increase security in a fundamental way, though it‘s a common practice.
D. IgnoreRhosts yes

Reasoning: This line, if present, actually increases security. The .rhosts file mechanism (and rhosts authentication) is highly insecure because it relies solely on IP addresses for authentication, which are easily spoofed. By setting IgnoreRhosts yes (which is often the default or recommended setting), you prevent the server from honoring .rhosts files, thereby closing a potential security hole. Therefore, you would not change this to increase security; you would ensure it remains yes.
E. Protocol 2, 1

Reasoning: This line specifies that both SSH Protocol 2 and Protocol 1 are allowed. SSH Protocol 1 has known cryptographic weaknesses and vulnerabilities and is considered insecure. To increase security, this line should be changed to Protocol 2 (or simply removed, as Protocol 2 is usually the default and preferred). Therefore, the change would be to remove 1, making it more secure. However, as stated, “if present, be changed in order to increase the security,“ and Protocol 1 is the insecure part. While one would change it, the existence of Protocol 1 in the line is the problem. If the options were Protocol 1 as an option, it would be incorrect, but Protocol 2, 1 itself means Protocol 1 is enabled. The best way to phrase a secure configuration would be Protocol 2. Given the choices and context of increasing security, removing Protocol 1 is the implicit action for this line, making its presence in the initial configuration a security weakness. However, PermitRootLogin yes and PermitEmptyPasswords no are much more direct and impactful security vulnerabilities to address.

Correct:

C. 0F
D. 0b
Reasoning:

The cache_dir directive for the ufs (Unix Filesystem) storage type in Squid uses a hierarchical directory structure to store cached objects. The format is:

cache_dir ufs [path] [size] [L1 directories] [L2 directories]

[path]: /var/spool/squid3/ – This is the root of the cache directory.
[size]: 1024 – The size of the cache in megabytes.
[L1 directories]: 16 – The number of first-level (L1) subdirectories. Squid creates these directories from 00 to 0F (in hexadecimal).
[L2 directories]: 256 – The number of second-level (L2) subdirectories within each L1 directory. These are created from 00 to FF (in hexadecimal).
Given 16 L1 directories, Squid will create directories named 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, and 0F directly within /var/spool/squid3/.

Therefore, 0F and 0B (which is 0b in lowercase as used in option D, as hexadecimal letters are case-insensitive in file names) are valid L1 directories that will exist directly within /var/spool/squid3/.

Incorrect:

A. A0

This would be a valid L2 directory name (if it existed within an L1 directory), but it is not a valid L1 directory name. L1 directories only go up to 0F.
B. FF

This is a valid L2 directory name (e.g., 00/FF), but it is not a valid L1 directory name. L1 directories only go up to 0F.
E. 0

Squid‘s ufs cache structure uses two-character hexadecimal names for its L1 and L2 directories, padding with a leading zero if necessary (e.g., 00, 01, 0A, 0F). A single digit 0 is not a valid directory name in this context.

Correct:

E. In /etc/sysctl.conf change net.ipv4.ip_forward to 1
Reasoning: The /etc/sysctl.conf file is the standard and most robust way to persist kernel parameters across reboots on Linux systems. Parameters set in this file are automatically loaded by the sysctl command during system startup (often via an init script or systemd unit). Changing the line to net.ipv4.ip_forward = 1 ensures that IP forwarding is enabled every time the system boots.
Incorrect:

A. Add echo 1 > /proc/sys/net/ipv4/ip_forward to the root user login script

Reasoning: Login scripts (like .bashrc, .profile, .bash_profile) are executed when a user logs in. This is not suitable for a system-wide setting like IP forwarding, which needs to be active regardless of whether root is logged in, and should ideally be set early in the boot process. Also, it‘s not a standard or reliable method for persistent kernel parameters.
B. Add echo 1 > /proc/sys/net/ipv4/ip_forward to any user login script

Reasoning: This is even worse than option A. IP forwarding is a global kernel setting, and a regular user‘s login script would not have the necessary permissions to modify /proc/sys/net/ipv4/ip_forward. Even if it did, it suffers from the same issues as A regarding persistence and timing.
C. In /etc/sysconfig/iptables-config add ipv4.ip_forward = 1

Reasoning: /etc/sysconfig/iptables-config (or similar files in /etc/sysconfig/) is typically used for configuration related to the iptables service itself, such as the location of the rules file or modules to load. It is not where kernel parameters are persistently set. Kernel parameters are managed by sysctl.
D. In /etc/rc.local add net.ipv4.ip_forward = 1

Reasoning: The /etc/rc.local script is an old System V init script mechanism that is executed at the end of the boot process. While it could work for setting parameters, it‘s considered deprecated in modern Linux distributions that use systemd. Even in older systems, using /etc/sysctl.conf is the more official and preferred method for kernel parameters. It‘s less robust and potentially less reliable than using sysctl.conf.

Correct:

C. It is used to determine the remote operating system.
Reasoning: TCP/IP stack fingerprinting, specifically with tools like nmap -O (for OS detection), works by sending a series of unique, non-standard TCP/IP packets to a target host and then analyzing the responses. Different operating systems and their TCP/IP implementations will respond in slightly different, characteristic ways (e.g., how they handle specific flags, initial window sizes, TTL values, TCP options, or even subtle bugs in their stack). nmap has a database of these “fingerprints“ and compares the target‘s responses against it to make an educated guess about the remote operating system and even its version.
Incorrect:

A. It is used to masquerade the responses of remote servers.

Reasoning: Masquerading responses means pretending to be a different server or altering the responses. TCP/IP stack fingerprinting is a passive or active identification technique, not an active manipulation or masquerading technique.
B. It is used to identify duplicate responses from the same remote server.

Reasoning: While analyzing responses is part of fingerprinting, the goal isn‘t to identify duplicates. It‘s to identify unique characteristics of the TCP/IP stack that reveal the OS. Duplicate responses are generally handled by the network stack itself to ensure reliable data transfer, not by fingerprinting.
D. It is used to filter out responses from specific servers.

Reasoning: Filtering responses is typically done by firewalls (like iptables or firewalld) or by the client application based on criteria other than the TCP/IP stack characteristics. Fingerprinting is about identifying, not filtering.
E. It is used to uniquely identify servers on the network for forensics.

Reasoning: While identifying the OS can be useful in forensics, TCP/IP stack fingerprinting itself isn‘t primarily about uniquely identifying individual servers for forensic purposes. Servers are uniquely identified by their IP addresses and potentially other network identifiers (like MAC addresses, though these are typically only useful on the local network segment). Fingerprinting provides OS information, which is a characteristic of the server, not its unique identity in the forensic sense.

Correct:

E. The configuration loads successfully.
Reasoning: The testparm command (and its samba-tool testparm equivalent for newer Samba versions) is specifically designed to check the syntax and validity of the Samba configuration files (smb.conf). It parses the configuration, reports any errors or warnings, and then typically displays the compiled configuration as Samba would interpret it. It confirms that the configuration can be loaded without errors, indicating proper syntax and valid directives. It does not test the runtime behavior of the services.
Incorrect:

A. The Samba services are started automatically when the system boots.

Reasoning: testparm is a configuration parser. It has no control over or knowledge of the system‘s init system (System V, systemd, etc.) or whether Samba services are enabled for automatic startup. That‘s managed by systemctl enable smbd or similar commands.
B. The service operates as expected.

Reasoning: testparm is a static configuration checker. It confirms the configuration syntax is correct, but it does not perform live tests of Samba‘s functionality (e.g., file sharing, authentication, Browse). To confirm a service operates as expected, you‘d need to actually connect to it from a client, check logs, or use specific diagnostic tools like smbclient.
C. All running Samba processes use the most recent configuration version.

Reasoning: testparm reads the configuration files from disk. It doesn‘t interact with running Samba processes to verify their loaded configuration. To make running Samba processes use a new configuration, you typically need to reload or restart the Samba services (e.g., systemctl reload smbd).
D. The netfilter configuration on the Samba server does not block any access to the services defined in the configuration.

Reasoning: testparm is only concerned with the Samba configuration itself (smb.conf). It has no knowledge of the system‘s firewall (netfilter/iptables/firewalld). Firewall rules are a separate layer of network security that must be checked independently.

Correct:

B. pam_limits
Reasoning: The pam_limits module is specifically designed to set resource limits for users, such as CPU time, file size, number of processes, and memory usage. These limits are defined in the /etc/security/limits.conf file (or files within /etc/security/limits.d/). This file allows administrators to specify different limits for individual users, groups, or ranges of UIDs/GIDs, directly matching the description of “an arbitrary file containing a list of user and group names with restrictions on the system resources available to them.“
Incorrect:

A. pam_filter

Reasoning: There isn‘t a standard PAM module widely known as pam_filter that fits this description in the context of resource limits. PAM modules typically have specific, well-defined functions (e.g., authentication, authorization, session management).
C. pam_unix

Reasoning: The pam_unix module (or pam_unix.so) is a core PAM module primarily responsible for traditional Unix password authentication and account management. It interacts with /etc/passwd, /etc/shadow, and /etc/group for user authentication, password changes, and account lockout policies. It does not manage system resource limits.
D. pam_listfile

Reasoning: The pam_listfile module is used for very general access control based on lists of users or items in a file. It can permit or deny access based on whether a username (or other item) is present or absent in a specified file. While it uses a “list of user… names,“ its purpose is access control (e.g., allow/deny login), not setting resource restrictions like CPU time or file size. It‘s a different type of restriction.

Correct:

D. SSLCertificateKeyFile
This is the correct Apache HTTPD directive to specify the path to the RSA (or other type) private key file associated with the SSL/TLS certificate. The server uses this private key to decrypt incoming requests and to prove its identity during the SSL/TLS handshake.
Incorrect:

A. SSLRSAKeyFile

While specifically mentioning “RSA,“ this is not a standard Apache HTTPD directive. Apache‘s SSL module (mod_ssl) uses SSLCertificateKeyFile regardless of the key algorithm (RSA, ECC, etc.).
B. SSLKeyFile

This is an outdated or non-standard directive. In older Apache versions, SSLKeyFile might have been used, but SSLCertificateKeyFile is the modern and correct directive as per mod_ssl documentation for specifying the private key.
C. SSLPrivateKeyFile

This might seem intuitive, but it is not the actual directive name used by Apache‘s mod_ssl. The correct directive is SSLCertificateKeyFile.

Correct:

A. There is no . after linuserv.example.net in the PTR record in the reverse lookup zone file

In a DNS reverse lookup zone file (used for PTR records), a trailing dot (.) after a fully qualified domain name (FQDN) like linuserv.example.net indicates the name is absolute and not relative to the zone’s origin. If the trailing dot is missing in the PTR record (e.g., 1.1.168.192.in-addr.arpa. IN PTR linuserv.example.net), the DNS server may append the zone’s origin (e.g., example.net), resulting in an incorrect name like linuserv.example.net.example.net. This misconfiguration can cause reverse DNS lookups to fail, which aligns with the issue implied by the question. For LPIC-2, understanding proper DNS zone file syntax, especially for PTR records in reverse zones, is critical.

Incorrect:

B. There is no . after linuserv.example.net in the PTR record in the forward lookup zone file

PTR records are not defined in forward lookup zone files; they are specific to reverse lookup zone files (e.g., 192.168.1.in-addr.arpa). Forward lookup zone files contain records like A, AAAA, or NS, mapping names to IPs, not IPs to names. Thus, this option is incorrect as it references an invalid context for PTR records.

C. The . in the NS definition in the reverse lookup zone has to be removed

The NS (Name Server) record in a reverse lookup zone file specifies the authoritative DNS server for the zone, typically including a trailing dot for an absolute FQDN (e.g., ns1.example.net.). Removing the dot would make the name relative, potentially causing resolution errors by appending the zone’s origin. This does not explain a failed DNS lookup with dig and is incorrect in the context of proper DNS configuration.

D. There is no . after linuserv in the PTR record in the forward lookup zone file

As with option B, PTR records do not exist in forward lookup zone files, making this option irrelevant. Additionally, linuserv alone (without the domain) is not a valid FQDN for a PTR record, and the issue of a missing dot after linuserv in a forward zone is not applicable. This option is incorrect due to its invalid context and terminology.

Correct:

D. acl

The missing word in the excerpt of a named.conf file is acl, which stands for Access Control List. In BIND’s configuration file (named.conf), the acl directive is used to define a named list of IP addresses, networks, or other criteria that can be referenced in other parts of the configuration, such as allow-query, allow-transfer, or allow-recursion. For example:

acl trusted {
192.168.1.0/24;
localhost;
};
allow-query { trusted; };
The acl keyword is essential for grouping IPs or networks to control access to the DNS server. This aligns with LPIC-2 objectives, which emphasize BIND configuration and access control for DNS services.

Incorrect:

A. list

The word list is not a valid keyword in named.conf. While it might seem plausible for grouping items, BIND uses acl for defining access control lists. This option is a distractor and does not apply to DNS configuration.

B. networks

The word networks is not a recognized keyword in named.conf. Although BIND can reference networks (e.g., 192.168.1.0/24) within an acl block, networks itself is not a directive. This option is incorrect as it does not match BIND syntax.

C. net

The word net is not a valid keyword in named.conf. It might be confused with network-related terms, but BIND uses acl to define groups of IP addresses or networks. This option is a distractor and incorrect for DNS configuration.

E. group

The word group is not used in named.conf for defining access control lists. While group might suggest grouping addresses, BIND specifically uses acl for this purpose. This option is incorrect as it does not align with BIND’s configuration syntax.

Correct:

C. It is not possible for Samba to use /etc/passwd and /etc/shadow directly

Samba cannot directly use /etc/passwd and /etc/shadow for CIFS password authentication. Samba requires its own password database, typically managed with the smbpasswd file or a backend like tdbsam, ldapsam, or passdb. While Samba can synchronize user accounts with /etc/passwd (e.g., using the pam_smbpass module or by importing users into the Samba database), it does not authenticate CIFS clients directly against /etc/passwd and /etc/shadow due to differences in password hashing and protocol requirements. For LPIC-2, understanding Samba’s password backend and its separation from system authentication is key.

Incorrect:

A. Set the parameters “encrypt passwords = yes”, “password file = /etc/passwd” and “password algorithm= crypt”

The “password file” parameter does not exist in Samba’s smb.conf, and “password algorithm = crypt” is not a valid option. While “encrypt passwords = yes” is a valid setting to enable encrypted passwords (required for modern CIFS clients), it does not configure Samba to use /etc/passwd or /etc/shadow directly. This option is incorrect due to invalid parameters and failure to address Samba’s authentication mechanism.

B. Set the parameters “encrypt passwords = yes” and “password file = /etc/passwd”

As with option A, “password file” is not a valid Samba configuration parameter. “encrypt passwords = yes” enables encrypted passwords but does not allow Samba to use /etc/passwd directly for CIFS authentication. This option is incorrect because it relies on a nonexistent parameter and does not solve the problem.

D. Delete the smbpasswd file and create a symbolic link to the passwd and shadow file

Deleting the smbpasswd file and creating symbolic links to /etc/passwd and /etc/shadow is not a valid configuration. Samba’s authentication system cannot read /etc/passwd or /etc/shadow through symbolic links, as it requires a specific password database format (e.g., smbpasswd or tdbsam). This approach would break Samba authentication and is incorrect for LPIC-2 configuration knowledge.

E. Run smbpasswd to convert /etc/passwd and /etc/shadow to a Samba password file

The smbpasswd command is used to manage Samba user passwords (e.g., adding users or changing passwords in the Samba database), but it does not “convert” /etc/passwd and /etc/shadow into a Samba password file. While users can be imported into the Samba database (e.g., using smbpasswd -a), this creates separate Samba credentials, not a direct conversion. This option is incorrect as it misrepresents the functionality of smbpasswd.

Correct:

E. The following line must begin with white space indentation.

In the main Postfix configuration file (main.cf), service definitions (and other parameters) can be continued on the next line by starting the continuation line with white space indentation (spaces or tabs). For example, in a parameter like relayhost, you might write:

relayhost = [smtp.example.com]:587
[smtp2.example.com]:587
The indented lines are treated as a continuation of the previous parameter. This is a standard convention in Postfix configuration for handling multi-line values, making this option correct for LPIC-2 knowledge of Postfix configuration syntax.

Incorrect:

A. The initial line must end with a backslash character ().

Postfix does not use a backslash () to indicate line continuation in main.cf. This is a common convention in other configuration files (e.g., shell scripts or some Linux config files), but Postfix relies on white space indentation for continuation. This option is incorrect.

B. The following line must begin with a plus character (+).

There is no requirement in Postfix configuration to begin continuation lines with a plus character (+). This is a distractor option and does not align with Postfix’s syntax, making it incorrect for LPIC-2.

C. It isn’t possible. The service definition must fit on one line.

This is incorrect because Postfix explicitly allows multi-line configurations in main.cf using white space indentation for continuation. Service definitions and other parameters can span multiple lines, so this option is false.

D. The service definition continues on the following lines until all of the required fields are specified.

While Postfix allows multi-line configurations, the continuation is not determined by “required fields” but by white space indentation on subsequent lines. This option misrepresents the mechanism, as continuation is not tied to field completion but to explicit indentation, making it incorrect.

Correct:

A. cn is the common name.

In an LDIF (LDAP Data Interchange Format) file, the cn attribute stands for common name. It is used to specify a user-friendly name for an LDAP entry, such as a person’s name, group name, or other identifier within the directory. For example, cn=John Doe identifies the common name of an entry. This is a standard LDAP attribute and aligns with LPIC-2 objectives for understanding LDAP schema and LDIF syntax.

Incorrect:

B. dn is the domain name.

The dn (distinguished name) in an LDIF file is not a domain name. It is a unique identifier for an entry in the LDAP directory, specifying its full path in the directory tree (e.g., dn: cn=John Doe,ou=Users,dc=example,dc=com). This option is incorrect as it misrepresents the purpose of dn in LDAP.

C. DC is the delegation container.

The dc attribute stands for domain component, not delegation container. It is used to represent components of a domain name in the LDAP hierarchy (e.g., dc=example,dc=com for the domain example.com). This option is incorrect due to the incorrect terminology and misunderstanding of dc.

D. o is the operator name.

The o attribute in LDAP represents the organization name, not the operator name. It is used to specify the name of an organization (e.g., o=Example Corp). This option is incorrect as it misinterprets the role of the o attribute in LDIF files.

E. dn is the relative distinguished name.

The dn (distinguished name) is the full, unique identifier for an LDAP entry, not the relative distinguished name (RDN). The RDN is the portion of the dn that uniquely identifies an entry within its parent container (e.g., cn=John Doe in dn: cn=John Doe,ou=Users,dc=example,dc=com). This option is incorrect because it confuses dn with RDN.

Correct:

A. “key.server.example.com. { algorithm hmac-md5; secret ““skrKc4DoTzi/takI1Pi7JZA==““; };“

To enable TSIG (Transaction Signature) in a BIND server for secure DNS transactions, a key statement must be added to the named.conf file. The correct syntax includes the key keyword followed by a name (e.g., server.example.com.), and a block defining the algorithm (in this case, hmac-md5) and the secret (the base64-encoded key, skrKc4DoTzi/takI1Pi7JZA==). The secret must be enclosed in double quotes, and each statement within the block ends with a semicolon (;). The entire key definition is enclosed in curly braces ({}) and terminated with a semicolon. This option matches the correct BIND syntax for TSIG configuration, aligning with LPIC-2 requirements for DNS security.

Incorrect:

B. “key.server.example.com. algorithm hmac-md5; secret ““skrKc4DoTzi/takI1Pi7JZA==;““

This option is syntactically incorrect because it lacks the curly braces ({}) required to enclose the key block in named.conf. Additionally, the structure is malformed, as the algorithm and secret statements are not properly grouped within a block. This does not follow BIND’s configuration syntax, making it incorrect for LPIC-2.

C. “key.server.example.com. { algorithm hmac-md5; secret skrKc4DoTzi/takI1Pi7JZA==; };“

This option is incorrect because the secret value (skrKc4DoTzi/takI1Pi7JZA==) is not enclosed in double quotes. In BIND, the secret for a TSIG key must be a quoted string (e.g., “skrKc4DoTzi/takI1Pi7JZA==“). Without quotes, BIND will fail to parse the configuration, rendering this option invalid.

D. “key.server.example.com. { algorithm=hmac-md5; secret ““skrKc4DoTzi/takI1Pi7JZA==““; };“

This option is incorrect because the algorithm parameter uses an equals sign (algorithm=hmac-md5) instead of a space (algorithm hmac-md5). In named.conf, parameters like algorithm are specified with a space, not an equals sign, as per BIND’s syntax. This error makes the configuration invalid.

E. “TSIG server.example.com. { algorithm hmac-md5 ; secret ““skrKc4DoTzi / tAkllPi7JZA ==““; };“

This option is incorrect for multiple reasons. First, TSIG is not a valid keyword for defining a key in named.conf; the correct keyword is key. Second, the secret value includes spaces and a forward slash (skrKc4DoTzi / tAkllPi7JZA ==), which does not match the provided key (skrKc4DoTzi/takI1Pi7JZA==). These errors make the configuration incompatible with BIND’s TSIG requirements.

Correct:

A. dig
dig (Domain Information Groper) is a flexible tool for interrogating DNS name servers. Without any options, simply running dig domain.com provides a verbose output that includes the question, answer section (with record type, class, TTL, and data), authority section, and additional section, along with statistical information about the query (query time, server, when, message size). This level of detail, especially the different sections and statistics, is typically more comprehensive by default than host or nslookup.
Incorrect:

B. nslookup

nslookup is an older, interactive tool for querying DNS. While it can provide useful information, its default output is generally less detailed and less structured than dig. Its interactive mode can be useful for quick lookups, but for comprehensive information in a single command, dig is superior.
C. named-checkzone

This tool is specifically used to check the syntax and integrity of a BIND DNS zone file. It does not perform live DNS queries or provide information about current DNS resolution. It‘s a configuration validation tool.
D. host

host is a simpler utility for performing DNS lookups. When used without options, it provides concise answers (e.g., A, AAAA, MX records). While convenient for quick checks, it typically offers less verbose information by default compared to dig, especially regarding the full DNS query/response structure and statistics.
E. named-checkconf

This tool is used to check the syntax and validity of the BIND DNS server‘s main configuration file (named.conf). It does not perform DNS queries or provide live DNS resolution information. It‘s a configuration validation tool for the BIND daemon itself.

Correct:

C. If the server does not know the answer to a query, it sends a recursive query to 192.168.0.4.

This implies the server is configured as a forwarder, delegating unresolved queries to 192.168.0.4 (likely an upstream DNS resolver).

Example named.conf snippet:

options {
forwarders { 192.168.0.4; };
forward only; # Optional: Strictly use forwarder, no root hints
};

A. Hosts on 10.0.0.0/24 can request zone transfers.

? False: Zone transfers are controlled by allow-transfer (not shown here). Without explicit rules, BIND denies all zone transfers by default.

B. Any host can use this server as their primary DNS.

? False: BIND restricts recursive queries via allow-recursion. Default is typically localhost/localnets only unless configured otherwise.

D. Sends queries to a root DNS server.

? False: This describes default recursive resolution (using root hints), but the correct answer (C) indicates forwarding is configured, bypassing root servers.

E. Sends recursive queries to 192.168.0.4 and returns failure if it fails.

? Partially correct but misleading:

If forward only; is set, BIND does not fall back to root servers (returns failure).

If forward first; (default), it falls back to root hints after forwarder fails.

The option is overly specific compared to (C).

Correct:

A. nc

Reasoning: nc (netcat) is a versatile networking utility often called the “TCP/IP Swiss Army Knife.“ It can be used to read from and write to network connections using TCP or UDP. Its simplicity and flexibility make it ideal for interacting with remote TCP services, sending arbitrary data, and receiving responses, allowing for direct communication and debugging. For example, nc hostname port will establish a TCP connection, and then you can type data to send or see data received.
C. telnet

Reasoning: telnet is primarily known as a remote login client, but it‘s fundamentally a client for the Telnet protocol, which operates over TCP. More broadly, it can establish raw TCP connections to any specified port and send/receive plain text, making it a common tool for testing and interacting with other TCP services (like HTTP, SMTP, POP3, IMAP) to see their raw banner or send basic commands. For example, telnet example.com 80 connects to an HTTP server, and you can then type HTTP requests.
Incorrect:

B. netmap

Reasoning: netmap is a framework for fast packet I/O in user space, primarily used for high-performance network applications (like firewalls, IDS, routers). It is not a user-level command-line utility for directly connecting and interacting with remote TCP services in the way nc or telnet are.
D. cat

Reasoning: cat is a command-line utility used to concatenate and display file content. It primarily works with local files and standard input/output. While it can be combined with other tools (e.g., pipes with nc) to send data, cat by itself cannot directly establish a TCP connection to a remote service.
E. nettalk

Reasoning: nettalk is not a standard or widely recognized Linux command-line utility for general TCP network service interaction. There might be obscure or specialized tools with similar names, but nc and telnet are the established utilities for this purpose on Linux systems as per LPIC-2 curriculum.

Correct:

B. Assignments of IPv6 prefixes that can be used for routing or further assignments.

Reasoning: DHCPv6 supports Prefix Delegation (PD), which allows a DHCPv6 server to assign an entire IPv6 prefix (e.g., a /48 or /56 subnet) to a requesting router. This prefix can then be used by the router to assign addresses to devices on its downstream networks (e.g., using Stateless Address Autoconfiguration – SLAAC) or for further sub-delegation. This is crucial for ISPs to allocate subnets to customer routers.
C. Assignments of temporary IPv6 addresses that cannot be renewed.

Reasoning: DHCPv6 supports the assignment of temporary addresses (Privacy Extensions), as defined in RFC 4941. These addresses are designed to change over time to enhance user privacy by making it harder to track a device‘s activity based on a static IP address. While these addresses are “temporary,“ the statement “cannot be renewed“ is generally incorrect or at least misleading in a strict sense. Temporary addresses can have lifetimes and can be re-issued or new ones generated by the client or server. However, in the context of distinguishing them from “normal“ addresses, their ephemeral nature is key, and the option focuses on that. The primary characteristic is their short, rotating lifetime for privacy, not their renewability in the same way a normal address is renewed. Self-correction: The phrasing “cannot be renewed“ is a bit tricky here, as temporary addresses do have lifetimes and new ones are generated. However, compared to “normal“ addresses designed for long-term assignment and explicit renewal, temporary addresses are meant to be short-lived and discarded/replaced. In the context of “types of assignments,“ providing privacy addresses is a distinct feature.
D. Assignments of normal IPv6 addresses that can be renewed.

Reasoning: This is the most straightforward and fundamental function of DHCPv6. It assigns standard, globally unique (or site-local) IPv6 addresses to clients, similar to how DHCPv4 assigns IPv4 addresses. These addresses typically have a finite lease time and can be explicitly renewed by the client before their lease expires. This is known as Stateful DHCPv6.
Incorrect:

A. Assignments of blacklisted IPv6 addresses that should no longer be used.
Reasoning: DHCPv6 (or any DHCP server) does not “assign“ blacklisted addresses. Blacklisting or excluding addresses is a function configured on the DHCP server to prevent it from assigning certain addresses or ranges. It‘s about what not to assign, not a type of assignment itself.

Correct:

D. Zone key files contain a public and private key.
Reasoning: When dnssec-keygen is used to create a DNSSEC key pair (whether it‘s a Key Signing Key – KSK or a Zone Signing Key – ZSK), it generates two files for each key: a .key file (containing the public key) and a .private file (containing the private key). These are distinct and separate files. The private key is kept secret on the authoritative server and used for signing. The public key is published in the DNS. This is true for both KSKs and ZSKs, which are collectively referred to as “zone keys“ in the context of signing a DNS zone.
Incorrect:

A. The host key files contain a public and private key.

Reasoning: In the context of DNSSEC, the term “host key“ is not standard for the keys used to sign DNS zones. DNSSEC uses zone keys (specifically KSKs and ZSKs) to sign records within a DNS zone. While a host might have SSH keys or other cryptographic keys, these are unrelated to DNSSEC. dnssec-keygen generates zone keys, not “host keys“ in this sense.
B. There is no difference.

Reasoning: This is incorrect because, as explained for option A, the concept of a “host key“ in the context of dnssec-keygen and DNSSEC zone signing is fundamentally different from “zone keys.“
C. Host keys must always be generated if DNSSEC is used; The zone keys are optional.

Reasoning: This is completely backward and incorrect terminology. As established, “host keys“ are not the relevant concept for DNSSEC zone signing. Furthermore, zone keys (KSK and ZSK) are mandatory if DNSSEC is being used to sign a zone, as they are the very mechanism by which the zone‘s records are cryptographically authenticated. Without zone keys, there is no DNSSEC signing.
E. Zone keys must always be generated if DNSSEC is used; Host keys are optional.

Reasoning: This statement correctly identifies that zone keys are mandatory for DNSSEC. However, it still incorrectly introduces the term “Host keys“ as if they are an optional part of DNSSEC. The term “Host keys“ is not applicable in the context of DNSSEC‘s mechanism for signing zones. The question is asking about the difference between these two types of keys, and since one (Host keys) is not a legitimate type in this context, the comparison implies a misunderstanding of DNSSEC terminology in the question itself, but option D correctly describes the nature of zone keys.

Correct:

E. fe80::/64
Reasoning: When IPv6 is activated on a network interface (even without manual global address configuration), the interface automatically configures a link-local address. Link-local addresses always start with fe80::/10 and are typically assigned with a /64 prefix, where the lower 64 bits are derived from the interface‘s MAC address (EUI-64 format). This link-local address is essential for communication with other devices on the same local link (segment) without the need for a router or global addressing. A route to the fe80::/64 prefix for that specific interface will automatically appear in the routing table, indicating that traffic to other link-local addresses on the same segment should be sent via this interface.
Incorrect:

A. fe80::/10

Reasoning: fe80::/10 defines the entire range of link-local addresses. While link-local addresses fall within this range, a specific route for a local interface will always be more granular, typically /64, which corresponds to the network prefix of the link-local address assigned to the interface itself. The route refers to the specific network segment that the interface is directly connected to, not the entire link-local address space.
B. 0::/128

Reasoning: 0::/128 is the unspecified address. It‘s used as a source address when a host doesn‘t yet have an assigned address (e.g., during DHCPv6 address request). It does not appear as a route in the routing table representing an active network interface or a destination.
C. 2000::/3

Reasoning: 2000::/3 is the global unicast address range (addresses assignable for public internet routing). While a router would eventually have routes to 2000::/3 networks once global addresses are configured and routing protocols are active, activating an interface and its link-local address alone does not automatically add routes to global unicast prefixes.
D. 0::/0

Reasoning: 0::/0 is the IPv6 equivalent of the default route (0.0.0.0/0 in IPv4). It means “any destination not otherwise specified.“ While a router will eventually have a default route, it‘s not automatically added simply by activating an interface. A default route is typically learned via a routing protocol, a static configuration, or Router Advertisements (RA). It‘s not a direct consequence of link-local address assignment.

Correct:

D. pam_env
Reasoning: The pam_env PAM module is specifically designed to set and unset environment variables for the user‘s session. It typically reads environment variable definitions from /etc/security/pam_env.conf and/or /etc/environment. This allows administrators to define session-specific environment variables based on user, group, or other PAM-related conditions, making it the perfect fit for the described purpose.
Incorrect:

A. pam_set

Reasoning: There is no standard PAM module named pam_set that is commonly used for setting environment variables. PAM modules follow specific naming conventions based on their function (e.g., pam_unix.so, pam_limits.so).
B. pam-vars

Reasoning: Similar to pam_set, pam-vars is not a standard or recognized PAM module for environment variable management.
C. pam_shell

Reasoning: While pam_shell is a PAM module, its primary purpose is to invoke a user‘s shell (e.g., /bin/bash). It doesn‘t directly set or unset arbitrary environment variables; rather, the shell itself would then process its own startup files which might set variables. It‘s not the module dedicated to this specific task within PAM.
E. pam_export

Reasoning: pam_export is not a standard PAM module. The module dedicated to environment variable handling is pam_env.

Correct:

B. anyof

Reasoning: In Sieve, the anyof control command implements a logical OR operation. If anyof is followed by a list of tests, the block of actions is executed if at least one of the tests evaluates to true. This allows you to combine multiple conditions where satisfying any one of them is sufficient to trigger the filter‘s actions.
D. allof

Reasoning: In Sieve, the allof control command implements a logical AND operation. If allof is followed by a list of tests, the block of actions is executed only if all of the tests evaluate to true. This allows you to combine multiple conditions where all must be met to trigger the filter‘s actions.
Incorrect:

A. and

Reasoning: While conceptually representing a logical AND, and is not a valid Sieve control command for combining multiple conditions. Sieve uses allof for this purpose.
C. noneof

Reasoning: noneof is a valid Sieve control command, and it implements a logical NOR (NOT OR) operation. If noneof is followed by a list of tests, the block of actions is executed if none of the tests evaluate to true. However, the question asks for statements that allow “logical combinations of conditions,“ and while noneof is a combination, anyof and allof are the more direct and fundamental “AND“ and “OR“ equivalents. Given the usual pairing in such questions, anyof and allof are the primary logical combinators.
E. or

Reasoning: Similar to and, or is not a valid Sieve control command for combining multiple conditions. Sieve uses anyof for this purpose.

Correct:

A. filter
Reasoning: The filter table is the default and most commonly used netfilter table. It‘s responsible for making decisions about whether to allow or deny packets as they traverse the system. It contains the three fundamental built-in chains for this purpose:
INPUT: For packets destined for the local host.
OUTPUT: For packets originating from the local host.
FORWARD: For packets being routed through the local host (i.e., not destined for or originating from the local host itself).
Incorrect:

B. nat

Reasoning: The nat (Network Address Translation) table is used for rules that modify packet source or destination addresses/ports. Its built-in chains are PREROUTING (for DNAT), POSTROUTING (for SNAT/masquerading), and OUTPUT. It does not contain INPUT or FORWARD as its primary function is address translation, not filtering.
C. masq

Reasoning: masq is not a netfilter table. “Masquerading“ is a form of Source Network Address Translation (SNAT) and is configured using rules in the nat table, typically in the POSTROUTING chain.
D. default

Reasoning: There is no netfilter table specifically named default. The filter table is the default table if none is specified for an iptables command, but default is not its name.
E. ipconn

Reasoning: ipconn is not a netfilter table. There are raw, mangle, and security tables in addition to filter and nat, but ipconn is not one of them.

Correct:

A. /var/named
Reasoning: On Linux systems running BIND (the most popular DNS server, often referred to as named), the default and most common location for storing DNS zone files is /var/named. This directory is typically owned by the named user and group, ensuring proper permissions and security for the zone data. In chroot environments, this path would be relative to the chroot jail (e.g., /var/named/chroot/var/named).
Incorrect:

B. /var/dns

Reasoning: While /var is a common location for variable data, /var/dns is not the standard or conventional directory for BIND zone files.
C. /etc/dns

Reasoning: The /etc directory is typically for configuration files (like named.conf), not for the actual zone data files themselves, which are considered “variable“ data that the named daemon reads and potentially updates (e.g., dynamic DNS).
D. /etc/named

Reasoning: Similar to /etc/dns, /etc/named is where you would typically find the main BIND configuration file (named.conf), but not the individual zone data files.

Correct:

B. Name resolution may be different for computers depending on their location.
Reasoning: This is the defining characteristic of split DNS (also known as split-horizon DNS). It involves having two (or more) different views of the DNS namespace, typically one for internal (private) clients and another for external (public) clients. Depending on where the client is located (e.g., inside the corporate network vs. on the internet), they will receive different DNS answers for the same hostname. For example, http://www.example.com might resolve to an internal IP address for employees inside the office, but to a public IP address for users on the internet.
Incorrect:

A. Complete recursive searches occur only if a forward search fails.

Reasoning: This describes a fallback mechanism for DNS resolution (e.g., trying a recursive resolver if a direct lookup fails or if an iterative search doesn‘t yield an answer), but it‘s not a feature unique to or defining of split DNS. Split DNS is about different answers based on source, not search order.
C. Searches from hostname to IP address and IP address to host occur on different servers.

Reasoning: This describes the separation of forward (A/AAAA records) and reverse (PTR records) DNS zones, which are often hosted on different servers or at least in different zone files. While common in DNS management, it‘s not the specific characteristic of split DNS, which is about different answers for the same name based on client location.
D. Hostnames can resolve to IP addresses, but not the other way around.

Reasoning: This implies a problem with reverse DNS, where PTR records are missing or misconfigured. It has nothing to do with the concept of split DNS, which handles both forward and reverse lookups, potentially with different answers, but generally allows both directions of resolution.

Correct:

C. is for reverse DNS resolution.
Reasoning: in-addr.arpa is a special top-level domain used exclusively for IPv4 reverse DNS lookups. When you perform a reverse DNS lookup (e.g., trying to find a hostname from an IP address), the query is constructed by reversing the IP address octets and appending .in-addr.arpa. For example, a lookup for 192.168.1.10 would query for 10.1.168.192.in-addr.arpa. Therefore, any zone defined in named.conf that ends with .in-addr.arpa is specifically configured to handle these reverse lookups.
Incorrect:

A. is valid on the Internet.

Reasoning: While in-addr.arpa zones are crucial for the proper functioning of the internet (allowing reverse lookups), the presence of in-addr.arpa in a zone name in named.conf itself doesn‘t mean the zone is valid on the Internet. It just means it‘s a reverse lookup zone. Its internet validity depends on proper delegation from its parent zone (e.g., your ISP‘s allocation for your public IP space) and correct configuration.
B. It is on another server.

Reasoning: The in-addr.arpa domain indicates the type of zone (reverse lookup), not its physical location. A reverse lookup zone can be hosted on the same server as forward zones, or on a different server, just like any other DNS zone.
D. is valid on the internal network.

Reasoning: in-addr.arpa zones are used for both internal (private IP ranges like 192.168.x.x) and external (public IP ranges) reverse DNS resolution. The domain itself doesn‘t restrict its use to one or the other. For private IP ranges, you would manage your own in-addr.arpa zones. For public ranges, your ISP delegates the reverse zone to you.