CCNA Network Services Security Questions

DHCP is incorrect because it only leases IP addressing information and other network parameters to clients; it does not translate hostnames to IP addresses, which is the core function of DNS.

NTP is incorrect as it is used solely for synchronizing clocks across network devices and does not handle any form of hostname or IP address resolution.

SNMP is incorrect because it is a protocol for monitoring and managing network devices, not for resolving hostnames or IP addresses.

Option C is incorrect because DNS does not assign IP addresses; this is the role of DHCP. Confusing these two services is a common error, but they serve distinct purposes in IP networking.

Option D is wrong because DNS does not replace default gateways. Default gateways are necessary for routing traffic between different networks, a function unrelated to DNS name resolution.

Option E is incorrect as DNS is unrelated to the Spanning Tree Protocol (STP), which manages Layer 2 loop prevention on VLAN trunks. DNS operates at higher layers for name resolution.

Incorrect. Layer 3 route loops are routing protocol issues and are not addressed by DHCP snooping, which operates at Layer 2 for DHCP message validation.

Incorrect. Trunk encapsulation mismatches relate to VLAN tagging and trunk negotiation, which DHCP snooping does not influence or prevent.

Incorrect. Weak SSH ciphers pertain to encryption security and have no connection to DHCP snooping, which focuses solely on DHCP message filtering.

Option B is incorrect because using PAT alone cannot guarantee a fixed public IP and port for the internal server. PAT dynamically assigns ports for outbound sessions, which prevents predictable inbound access to the server from outside.

Option C is incorrect because private IPv4 addresses are not routable on the public Internet. Disabling NAT would make the internal server unreachable externally, violating the requirement for consistent outside access.

Option D is incorrect because DHCP relay only forwards DHCP requests between clients and servers and does not affect NAT or the server's public reachability. It does not solve the problem of making the internal web server accessible from outside.

This option is wrong because 203.0.113.10 is the inside global address, not the inside local address. The inside local address is 192.168.10.25, which is correctly identified in option A.

This option is incorrect because 198.51.100.20 is the outside local address, not a translated private address. The inside local address is specifically 192.168.10.25, as indicated in the NAT translation entry.

This option is incorrect because the entry shows that 203.0.113.10 is the inside global address, not the inside local address. The inside local address is 192.168.10.25, which is correctly identified in option A.

The ip directed-broadcast command enables forwarding of directed broadcasts but does not relay DHCP requests. It is unrelated to DHCP relay and will not solve the problem of clients not receiving addresses from a remote DHCP server.

service dhcp-server is not a valid Cisco IOS interface command for DHCP relay. It does not configure the router to forward DHCP broadcasts and thus will not resolve the issue.

default-router is a DHCP pool parameter used to assign the default gateway IP address to clients. It does not configure the interface to relay DHCP broadcasts and is not relevant to the relay configuration.

Incorrect because DHCP relay only forwards DHCP requests and does not provide any mechanism for publishing an internal server to the Internet or managing NAT translations.

Incorrect because disabling NAT leaves the internal server with a private IP address that is not routable on the Internet, making it unreachable from outside networks.

Incorrect because moving the server into the native VLAN affects only Layer 2 segmentation and does not provide a public IP address or NAT translation necessary for Internet access.

Uses `ntp master` without a stratum number, defaulting to stratum 8 instead of the required stratum 5.

Sets the wrong time zone (EST) instead of UTC.

Points to the ISP IP 10.0.0.2 instead of the actual NTP server at 192.168.1.200.

The number range 100–199 is used for extended ACLs, not standard ones.

The placement advice is reversed: standard ACLs belong near the destination, not the source.

This is a common misconception; the ability to delete individual ACEs is a feature of named ACLs, not numbered.

PAT overload is incorrect because it is designed for many internal clients sharing a single public IP for outbound traffic, not for providing a fixed public IP to a server.

No NAT is incorrect since private IPv4 addresses are not routable on the Internet and require NAT to be accessible externally.

DHCP relay is unrelated to NAT or public reachability; it only forwards DHCP requests and does not affect how internal servers are accessed from outside.

Option A incorrectly states that 'O IA' is an external route redistributed from another routing protocol. In reality, 'O IA' stands for inter-area routes within OSPF, not external routes. External routes use 'O E1' or 'O E2' codes.

Option C incorrectly claims that 'O' means the route was learned through EIGRP. The 'O' code is exclusive to OSPF intra-area routes. EIGRP routes use the code 'D' in Cisco routing tables.

Option D is incorrect because the three routes represent different OSPF route types: intra-area (O), inter-area (O IA), and external (O E2). They do not all come from the same OSPF area type.

Loop Guard is incorrect because it protects against unidirectional link failures by preventing a port from transitioning to forwarding when BPDUs stop, but it does not disable a port upon BPDU receipt.

Root Guard is incorrect because it prevents a port from becoming a root port by blocking superior BPDUs but does not disable the port immediately when a BPDU is received on an edge port.

UDLD is incorrect because it detects unidirectional physical link failures and does not interact with BPDU processing or disable ports based on BPDU reception.

Incorrect. DHCP exhaustion would prevent some clients from obtaining IP addresses, but it does not cause RF interference or a sharp drop in wireless throughput. Since users can connect, DHCP exhaustion is unlikely.

Incorrect. An authentication mismatch would prevent clients from connecting to the SSID. Since users can connect, authentication is working properly and is not the cause of performance degradation.

Incorrect. A missing default route on the wireless controller affects upstream network connectivity but does not cause local RF interference or throughput drops in the wireless environment.

Incorrect. The device key is enclosed in curly braces, making it a JSON object, not an array. It groups hostname and interfaces under one entity.

Incorrect. The status field is a string within each interface object, not an array. Each interface has its own status string indicating up or down.

Incorrect. The hostname is a string property directly inside the device object and is not nested inside the interfaces array or any other array.

The SVI must have an IP address for routing, but the DHCP server can serve addresses from any pool regardless of the SVI's subnet. The issue is with the pool itself.

If DHCP snooping were blocking messages, the 'Malformed messages' counter might increase, but the server would still receive some messages. The zero count indicates no messages are reaching the server.

There is no 'vlan' command under a DHCP pool. The pool serves all hosts in the subnet regardless of VLAN association.

This option is incorrect because administratively shutting down unused switch ports does not enforce SSH for device management; it simply disables unused ports to enhance security.

This option is wrong because administratively shutting down unused switch ports does not convert remaining ports into trunk ports; it simply disables access ports to enhance security.

This option is wrong because administratively shutting down unused switch ports does not directly replace VLAN segmentation; rather, it focuses on reducing the number of active ports to mitigate security risks.

STP (Spanning Tree Protocol) is incorrect because it operates at Layer 2 to prevent network loops and does not handle hostname resolution or IP services.

PAT (Port Address Translation) is incorrect because it translates private IP addresses to public IPs for outbound traffic but does not affect DNS or hostname resolution.

Port security is incorrect because it controls access to switch ports based on MAC addresses and does not provide or affect hostname resolution services.

Incorrect. The ACL in NAT configurations is used to identify which inside addresses to translate, not to filter or deny traffic. Denying RFC1918 traffic in the ACL is unnecessary and unrelated to the NAT failure described.

Incorrect. Using the outside interface IP address for PAT overload is a standard and supported practice in Cisco NAT configurations. This option does not explain the return traffic failure.

Option C is incorrect because accounting only logs user activities and does not replace the need for local usernames or authentication sources on Cisco devices.

Option D is incorrect as AAA supports both RADIUS and TACACS+ protocols; it is not limited to RADIUS, and TACACS+ is commonly used for device administration.

The specific factual error is that the authentication list must include 'group radius' to use RADIUS; 'local' alone bypasses RADIUS.

The specific factual error is omitting 'local' from the authentication list, which violates the requirement for fallback.

The specific factual error is confusing 'aaa authentication login' with 'aaa authentication dot1x'. They serve different purposes.

SYN flood is a Layer 4 TCP attack that is blocked by flood guards, not by DAI.

Route summarization error is a routing protocol misconfiguration and is unrelated to ARP packet validation.

Rogue DHCP relay is mitigated by DHCP snooping, not by Dynamic ARP Inspection.

Candidates assume that any missing traffic must be explicitly permitted, but this ignores the need for stateful inspection and leads to an overly permissive rule.

Candidates mistakenly think that moving the ACL to inbound direction will inherently permit return traffic because it inspects packets entering the interface, but the ACL still processes each packet individually without keeping state.

Candidates may think that only a stateful firewall can handle return traffic, overlooking the established keyword's capability to emulate stateful behavior for TCP traffic on an ACL.

This option is incorrect because PAT overload uses a different command syntax involving 'overload' and allows many internal hosts to share one public IP, which is not the case here.

This option is wrong since static NAT does not inherently block inbound access; instead, it enables external hosts to reach the inside host via the mapped public IP.

This option is incorrect because NAT translation does not modify the subnet mask of the inside host; it only changes the IP address seen externally.

The 'restrict' mode allows frames from unauthorized MAC addresses to be dropped while sending SNMP traps and syslog messages, which contradicts the requirement of keeping the interface up without notifications.

The 'shutdown' mode disables the interface when a violation occurs, which is contrary to the requirement of keeping the interface up. It also does not align with the need to drop frames without sending SNMP traps or syslog messages.

The 'shutdown vlan' mode disables the entire VLAN when a violation occurs, which is not aligned with the requirement to keep the interface up. This option also typically sends SNMP traps or syslog messages, which contradicts the question's criteria.

This describes the capability of extended ACLs, not standard ACLs.

Protocol filtering is a feature of extended ACLs, not standard ACLs.

Both inbound and outbound application are possible, though placement depends on the filtering strategy.

Candidates may confuse security inspection with NAT translation, assuming that a protocol‑specific inspection is needed for HTTP.

Tempting because an ACL could selectively block TCP; however, the question provides context about the renumbering, which directly points to the NAT configuration.

Candidates may assume that different protocols might take different paths, but a single default route applies uniformly to all IP traffic.

HTTPS uses TCP, not UDP.

Standard ACLs cannot filter by port; extended ACLs are required.

Extended ACLs support host destinations; a wildcard subnet is not required for a specific host.

This option is incorrect because DHCP does not replace DNS. DNS is a separate service responsible for name resolution, while DHCP only provides IP configuration parameters including DNS server addresses.

This option is wrong because DHCP does not remove the need for default gateways. Hosts still require gateway information to communicate outside their subnet, and DHCP typically provides this information during configuration.

This option is incorrect because routing protocols do not depend on DHCP. Routing protocols function independently of IP address assignment methods and do not require DHCP to operate on user networks.

TACACS+ encrypts only the password and is designed for device administration, not for 802.1X authentication which requires EAP support—RADIUS is the correct choice.

The global command 'aaa new-model' enables the AAA architecture but does not automatically enable 802.1X on interfaces; additional commands like 'dot1x system-auth-control' and per-interface 'authentication port-control auto' are needed.

802.1X requires the switch port to be in access mode, not trunk mode; trunk ports do not support 802.1X because multiple VLANs would conflict with the authentication process.

This option is incorrect because ARP is used for local subnet communication and does not depend on the presence of a default gateway. The host can still use ARP to communicate locally.

This option is wrong because a host does not automatically become part of every remote subnet without a gateway. The subnet mask defines the local subnet boundaries, and gateway absence does not change this.

This option is unrelated to the problem. Converting an access port to a trunk port affects VLAN tagging on switches but does not impact a host’s ability to have or use a default gateway.

This option is wrong because the ACL only permits TCP traffic on port 443 and ICMP traffic, so an HTTP packet (port 80) from the specified source would be denied by the implicit deny rule at the end of the ACL.

This option is wrong because NAT does not occur before ACL evaluation; the ACL is applied directly to the packet as it arrives at the interface. Therefore, the HTTP packet is evaluated against the ACL without any translation taking place.

This option is wrong because the ACL does not automatically convert HTTP traffic to HTTPS; it only permits or denies traffic based on the defined rules. The packet from 10.10.10.25 is not permitted by the ACL since it is not targeting port 443.

The static NAT command syntax is 'ip nat inside source static [inside-local] [inside-global]'. Here, the inside local (private) should be 172.16.1.100 and inside global (public) should be 10.0.0.3. Also, the inside interface is the one facing the internal network (G0/1) and outside is facing the ISP (G0/0).

NAT requires that the interface facing the internal network be marked as 'ip nat inside' and the interface facing the external network be marked as 'ip nat outside'. Here, G0/0 connects to the ISP (outside) and G0/1 connects to the internal network (inside).

The command 'ip nat outside source static' translates the source address of packets arriving on the outside interface. For translating internal host addresses to a public IP, 'ip nat inside source static' must be used.

Candidates may focus on Hits: 0 and Misses: 15042 as typical of an ACL issue, but the explicit interface binding in the dynamic mapping is the direct evidence of misconfiguration.

The high CEF Punted count mirrors the misses, leading some to believe CEF is the problem, but the exhibit does not indicate CEF is disabled.

Candidates might assume that a high miss count reflects a full translation table, but the total active translations show 0.

Incorrect because if the server were in the wrong VLAN, users would not be able to reach it by IP address. Successful IP access proves VLAN membership is correct.

Incorrect because a missing default gateway would prevent IP connectivity to the server if it were on a different subnet. Since IP access works, the default gateway is present and functional.

Incorrect because GRE tunnels are unrelated to hostname resolution. Hostname access depends on DNS, not tunneling protocols like GRE.

Incorrect because the DF bit explicitly forbids fragmentation; the router cannot fragment the packet if DF is set.

Incorrect because routers do not clear the DF bit to fragment packets; they respect the DF bit as set by the source.

Incorrect because GRE encapsulation is unrelated to MTU handling and fragmentation behavior.

The helper-address must be the IP of the DHCP server, which is the SVI address 192.168.50.1, not the link address 10.0.0.1.

The helper-address misconfiguration prevents DHCP requests from being forwarded to the correct server, so fixing only the excluded range is insufficient.

The excluded range must be corrected to allow hosts to receive addresses from the pool; otherwise, the DHCP server will not assign addresses.

This option is incorrect because ARP is used for local Layer 2 address resolution and remains functional even if the default gateway is missing; the host can still resolve MAC addresses on the local subnet.

This option is incorrect because the host’s subnet membership is determined by its IP address and subnet mask, not by the presence or absence of a default gateway; it does not join other subnets automatically.

This option is incorrect because a host does not become a default gateway for other devices simply by lacking a configured gateway; routing and gateway roles require explicit configuration on routers.

Option B incorrectly identifies severity level 3 as Emergency; level 3 actually represents Error, which is serious but less critical than Emergency (0).

Option C incorrectly identifies severity level 5 as Emergency; level 5 is Notification, which indicates normal but significant conditions, not emergencies.

Option D incorrectly identifies severity level 7 as Emergency; level 7 is Debugging, the lowest severity level used for detailed troubleshooting information.

Incorrect because Spanning Tree Protocol (STP) root bridge election affects Layer 2 switching topology, not Layer 3 NAT translation or routing on the WAN interface.

Incorrect because voice VLAN configuration on branch access switches does not influence NAT translation or whether private IP addresses are translated on the WAN interface.

Incorrect because a loopback interface IP address does not affect PAT translation of inside user traffic; PAT depends on NAT ACLs and routing, not loopback IP addresses.

The DNS server option is not critical for basic connectivity to remote networks; it primarily affects name resolution. If a client can obtain an IP address but cannot reach remote networks, the issue is more likely related to the default gateway configuration.

The lease time option specifies how long a DHCP lease is valid, but it does not affect the ability to reach remote networks. Therefore, a missing or incorrect lease time would not directly cause connectivity issues.

The TFTP server option is not necessary for a client to reach remote networks, as it primarily facilitates file transfers and does not impact routing or network accessibility. Therefore, its absence would not directly cause connectivity issues to remote networks.

Converting unused ports into a trunk does not prevent unauthorized access; it actually allows multiple VLANs to be carried over a single link, potentially exposing sensitive data. This action could inadvertently grant access to unauthorized devices if they connect to these trunked ports.

Enabling Telnet on unused ports does not prevent unauthorized access; instead, it creates a potential security vulnerability by allowing remote access to those ports. This action could expose the network to unauthorized monitoring or control.

Removing VLAN assignments from active user ports does not prevent unauthorized devices from accessing the network; it could disrupt legitimate user access instead. The goal is to secure unused ports, not impact active ones.

A common mistake is to try to explain zero matches by directional misapplication without first checking whether an ACL is actually present. The exhibit explicitly shows no ACL is bound.

Some candidates fixate on ACL configuration details instead of verifying interface assignment. The output confirms the interface has no ACL, not that an ACL is configured incorrectly.

Candidates sometimes misread interface status. This output clearly shows the interface is enabled and up, so a down state is not the issue.

This option is incorrect because shutting down unused switch ports does not directly increase available bandwidth; rather, it is a security measure to minimize potential vulnerabilities. Bandwidth on the switch backplane is determined by the overall switch architecture and the active ports' configurations, not by disabling unused ports.

This option is wrong because administratively shutting down unused switch ports does not enable 802.1Q trunking; trunking is a configuration that allows multiple VLANs to traverse a single physical link, which is unrelated to the status of unused ports.

This option is wrong because administratively shutting down unused switch ports does not automatically activate port security; it is a separate configuration that must be enabled explicitly on the switch.

Incorrect because the remote host’s MAC address is not known to the sender and cannot be resolved via ARP across subnets. The host must send to the gateway’s MAC instead.

Incorrect because broadcast MAC addresses are used only for ARP requests or broadcast traffic, not for normal unicast data frames to a specific remote IP.

Incorrect because a device’s own MAC address is used as the source MAC in frames it sends, never as the destination MAC.

This option is incorrect because SSH does not inherently use less bandwidth than Telnet; both protocols utilize TCP, and SSH's encryption actually adds overhead, potentially increasing bandwidth usage.

This option is incorrect because SSH can operate over various types of connections, including console ports, but it is not limited to them. Telnet can also be used over console ports, making this statement misleading.

This option is incorrect because SSH does require user authentication, typically through passwords or public key authentication, which is essential for secure access. In contrast, Telnet does not enforce strong authentication mechanisms.

Incorrect. Standard ACLs cannot match TCP or UDP port numbers; this capability belongs to extended ACLs, which provide more granular filtering.

Incorrect. ACLs do not automatically create a 'permit any' at the end; instead, they have an implicit deny all statement that blocks any traffic not explicitly permitted.

This option is incorrect because NTP does not replace Syslog; Syslog is responsible for logging events, while NTP only synchronizes time.

This option is incorrect because IP address assignment is handled by DHCP, not NTP, which only manages time synchronization.

This option is incorrect because NTP has no role in providing WLAN encryption; encryption is managed by wireless security protocols like WPA2 or WPA3.

The root cause is a missing A record; a CNAME record would not resolve without an A record for the target.

PTR records are not used for forward name resolution; the issue is with the forward lookup zone.

The zone delegation is working (other records resolve), so NS records are not the cause.

The direction does not change the fact that the 'established' keyword only permits packets with ACK/RST flags, which excludes the initial SYN.

The problem is specifically with TCP connections and ICMP echo-replies, not DNS or UDP.

The wildcard mask is already appropriate; the problem lies in the 'established' keyword.

DNS resolves hostnames to IP addresses, enabling devices to locate servers and services by name. However, DNS does not synchronize device clocks or manage time, so it cannot ensure matching timestamps in logs.

TFTP is a simple protocol used for transferring files such as configurations and IOS images. It does not provide any time synchronization capabilities and cannot ensure matching timestamps in device logs.

NetFlow is a network protocol that collects and exports IP traffic flow information for analysis. It does not affect device clocks or time synchronization and thus cannot provide matching timestamps.

Root Guard prevents a port from becoming a root port if superior BPDUs are received, maintaining the root bridge position, but it does not err-disable the port upon BPDU receipt. Therefore, it does not fulfill the requirement to disable access ports that receive BPDUs.

Loop Guard protects against unidirectional link failures by preventing a port from transitioning to forwarding state if BPDUs stop arriving on non-designated ports. It does not disable ports upon receiving BPDUs, so it does not meet the behavior described in the question.

PortFast is a feature that allows ports to transition quickly to forwarding state, bypassing the usual STP listening and learning states. It does not disable ports upon receiving BPDUs and therefore does not provide the behavior described.

The specific factual error is that the static NAT inside address is already correct; altering it is unnecessary and incorrect.

The specific factual error is that static NAT is required for inbound access; PAT alone cannot provide a fixed public-to-private mapping.

The specific factual error is that interface NAT direction is fundamental; if inside/outside are reversed, NAT translations will not be applied correctly.

Named standard ACLs filter traffic only by source IP address and cannot filter by destination IP or specific TCP ports like 80 or 443, making them unsuitable for permitting HTTP and HTTPS to a specific server.

Prefix lists are used to filter routes based on IP prefixes in routing protocols and cannot filter traffic by protocol or port, so they cannot meet the requirement to permit HTTP and HTTPS traffic specifically.

MAC access-lists filter traffic based on Layer 2 MAC addresses and cannot filter by Layer 3 IP addresses or Layer 4 ports, so they cannot selectively permit HTTP and HTTPS traffic to a specific IP address.

The helper-address must point to the DHCP server, not the default gateway. The excluded-address range should include the gateway to prevent conflicts.

The excluded-address range must be limited to reserved addresses only, not the entire usable range. The helper-address must be corrected to 10.0.0.1.

DHCP snooping requires the port connected to the legitimate DHCP server to be explicitly trusted; otherwise, all DHCP server messages are discarded.

The specific factual error is that 'ip domain lookup' enables DNS client functionality but does not specify which DNS server to use. The command is already present, so reconfiguring it does not fix the missing server IP.

The specific factual error is that the domain name is already configured correctly; changing it would not address the empty name-server list.

The specific factual error is that debugging is a diagnostic tool, not a corrective action. The question asks to 'fix' the issue, not just diagnose it.

It is a supporting feature for relay agents, not the primary command to forward DHCP broadcasts.

It is a prerequisite but not sufficient; the ip helper-address is still needed to direct the traffic.

The command does not exist; it is a fabrication.

Syslog is incorrect because it focuses on logging event messages and alerts rather than routinely polling device counters or CPU statistics, so it does not meet the periodic monitoring requirement.

NetFlow is incorrect because it provides detailed traffic flow analysis and visibility but does not poll general device statistics like CPU usage or interface counters, which are needed here.

Port security is incorrect because it is a Layer 2 feature that restricts MAC addresses on switch ports and does not provide any monitoring or polling capabilities for device statistics.

Administrators often mistake 'connection refused' for a key issue, but the VTY lines restrict the allowed protocols, not the validity of the keys.

Candidates may think a version mismatch causes the refusal, but the VTY transport setting is the actual filter; downgrading security is unnecessary and ineffective.

Some technicians equate 'connection refused' with authentication failure and jump to AAA, but in this case the VTY lines never allow the SSH session to reach the authentication stage.

HTTPS uses TCP, not UDP, so a UDP permit for port 443 would not match HTTPS traffic.

The ACL reverses source and destination; it denies Telnet from any to 10.1.50.0/24, not from 10.1.50.0/24 to any.

Permitting all IP traffic would allow Telnet, negating the required deny rule.

An empty NAT table indicates no translation is happening at all, which is not the expected outcome of simply reversing inside/outside roles—NAT still processes packets but incorrectly.

Complete internet unreachability is a generic connectivity symptom that could be caused by routing, firewall, or other NAT issues, but does not strongly signal a role reversal.

External hosts connecting to a private IP without translation is a typical sign of a missing static NAT or PAT rule, not of reversed interface direction assignments.

The command 'access-group' is used on interfaces to filter traffic, not on VTY lines. VTY lines use 'ip access-class' to filter incoming Telnet/SSH sessions.

The direction 'out' on VTY lines filters traffic originating from the router (outgoing), not incoming SSH connections. The correct direction is 'in'.

The command 'transport input all' permits all protocols, including Telnet, which is insecure. The requirement specifies SSH only, so 'transport input ssh' is needed.