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Question 21
A branch office reports intermittent connectivity to cloud storage, while other internet services work fine. What should be checked first?
A) DNS server configuration
B) Cable labeling scheme
C) Console port baud rate
D) DHCP lease duration
Answer: A)
Explanation:
Intermittent access to cloud storage while other services remain unaffected indicates a potential name resolution issue rather than a full connectivity problem. DNS servers translate human-readable hostnames into IP addresses, allowing applications to locate cloud services correctly. If the DNS configuration is incorrect, outdated, or partially failing, specific services—like cloud storage—may become unreachable intermittently.
The administrator should verify primary and secondary DNS entries on both the branch router and the endpoints. This includes checking for proper forwarding, caching behavior, and zone resolution. Also, examining DNS query logs can reveal timeouts, failed resolutions, or misrouted queries. Sometimes, external cloud services might have their IP addresses updated, and cached DNS records on the branch or ISP DNS may not reflect these changes, leading to intermittent failures.
Option B) cable labeling scheme is purely administrative and does not influence DNS resolution or cloud connectivity.
Option C) console port baud rate only affects local device management and cannot impact network traffic.
Option D) DHCP lease duration controls IP address assignment timing, but if devices already have valid IP addresses, lease timing does not affect cloud service accessibility.
Therefore, checking DNS server configuration is the first and most logical step to troubleshoot selective connectivity issues to cloud services. Ensuring proper DNS operation restores reliable access to cloud applications without affecting general internet traffic.
Question 22
During peak hours, users complain of slow database responses over a WAN link. What should be examined first?
A) WAN QoS and traffic prioritization
B) Switch firmware versions
C) VLAN naming conventions
D) Patch panel organization
Answer: A)
Explanation:
When database performance drops specifically during peak WAN usage, it indicates that high-volume traffic may be contending with critical application flows. Quality of Service (QoS) policies on WAN links regulate traffic by assigning priorities to different applications. Without proper QoS, bulk transfers or non-critical traffic can saturate the link, causing latency and packet loss that impact database responsiveness.
The administrator should review classification rules, traffic shaping policies, and queue configurations to ensure database traffic is prioritized over lower-priority flows. Monitoring WAN utilization statistics during peak hours can also identify which traffic types are consuming bandwidth excessively. Correctly configured QoS prevents congestion and maintains consistent performance for mission-critical applications.
Option B) switch firmware affects device operation but does not directly influence WAN traffic prioritization.
Option C) VLAN naming is organizational and has no effect on traffic shaping.
Option D) patch panel organization is administrative and irrelevant to performance over WAN links.
Thus, examining WAN QoS and traffic prioritization is the essential first step in resolving slow database responses during periods of heavy network utilization.
Question 23
A network team notices that wireless clients intermittently drop connections when multiple APs overlap on the same channel. What should be verified first?
A) Wireless channel assignments and overlap
B) DHCP lease times
C) Access point console passwords
D) Ethernet cable colors
Answer: A)
Explanation:
Wireless clients dropping intermittently when multiple APs share channels usually indicates co-channel interference. Overlapping channels create contention for the same frequency, leading to packet loss, retransmissions, and intermittent disconnects. Verifying wireless channel assignments ensures that nearby APs operate on non-overlapping channels, reducing interference and improving client stability.
The administrator should conduct a site survey or use spectrum analysis tools to identify overlapping channels and adjust AP configurations. Deploying channels 1, 6, and 11 in the 2.4 GHz spectrum, for example, can minimize interference. In high-density environments, proper channel planning and load balancing across APs are critical to prevent performance degradation.
Option B) DHCP lease times impact IP assignment but do not cause intermittent wireless disconnections.
Option C) access point console passwords do not affect wireless connectivity.
Option D) Ethernet cable colors are organizational and irrelevant to Wi-Fi operation.
Thus, checking wireless channel assignments and overlap is the logical first step in resolving intermittent client disconnections caused by interference in dense wireless environments.
Question 24
A core router drops packets intermittently during large file transfers between two sites. What should be examined first?
A) MTU settings along the path
B) Router hostname
C) NTP synchronization
D) Cable label sequence
Answer: A)
Explanation:
Intermittent packet loss during large file transfers often points to MTU mismatches along the path. If the router or an intermediate device cannot accommodate the packet size without fragmentation and ICMP messages are blocked, packets are silently dropped, causing transfer errors.
The administrator should perform a path MTU discovery or test with “don’t fragment” ping packets to identify the hop that cannot handle the full packet size. Ensuring consistent MTU across all devices, including VPN tunnels or encapsulation headers, prevents drops and improves reliability during large transfers.
Option B) router hostname is administrative and unrelated to packet handling.
Option C) NTP synchronization affects timestamps but does not influence packet forwarding.
Option D) cable label sequence is organizational and irrelevant to packet delivery.
Hence, examining MTU settings along the path is the essential first step to prevent packet loss during high-volume transfers between sites.
Question 25
Users cannot access certain web applications intermittently, while email traffic works fine. What should be verified first?
A) Firewall rules and application filtering
B) DHCP lease duration
C) Switch port speed settings
D) Cable management sequence
Answer: A)
Explanation:
Selective web application access issues indicate that traffic is being filtered or blocked, rather than a full network outage. Firewalls may have rules, URL filters, or application inspection features that permit email but restrict specific web applications. Verifying firewall rules ensures that legitimate application traffic is allowed and that filtering policies are correctly applied.
The administrator should check firewall logs, rule priorities, NAT settings, and any application-layer inspection features. Misconfigured policies, outdated application signatures, or incorrect URL categories can cause intermittent blocking while other services remain functional. Correcting firewall rules restores consistent access for all authorized web applications.
Option B) DHCP lease duration affects IP assignment but does not selectively block web traffic.
Option C) switch port speed impacts local link performance but is unlikely to selectively affect application traffic.
Option D) cable management is administrative and has no effect on firewall-based traffic filtering.
Therefore, reviewing firewall rules and application filtering is the critical first step to resolve intermittent web application access issues while ensuring email and other services remain unaffected.
Question 26
A corporate network experiences high latency during peak hours, particularly affecting VoIP calls, while file transfers remain stable. What is the most likely cause?
A) Improper WAN QoS configuration
B) DHCP server misconfiguration
C) VLAN ID mismatch
D) Incorrect console port speed
Answer: A)
Explanation:
High latency specifically affecting VoIP traffic while bulk file transfers remain stable usually points to a Quality of Service (QoS) issue rather than general bandwidth limitations. QoS is a mechanism to prioritize traffic based on application type, sensitivity to latency, and importance to the business. VoIP is highly latency-sensitive because delayed packets directly affect voice quality, resulting in choppy audio, dropped calls, or jitter.
In this scenario, file transfers remain stable because they are not time-sensitive and can tolerate delays, whereas VoIP traffic requires low latency, low jitter, and minimal packet loss. Improper QoS configuration often occurs in the following ways:
No prioritization of VoIP traffic: All packets are treated equally, allowing bulk traffic like file transfers to consume bandwidth first, leading to delays in voice packets.
Misclassified traffic: VoIP packets may be incorrectly tagged, so switches and routers fail to recognize them for priority treatment.
Insufficient queue allocation: Even with proper prioritization, queues for high-priority traffic may be too small, causing overflow during peak usage.
Troubleshooting should include verifying that VoIP traffic is correctly classified, DSCP (Differentiated Services Code Point) tags are applied properly, and queues are configured on WAN interfaces to give priority to low-latency applications. Monitoring tools like Wireshark, network analyzers, or built-in router QoS statistics can identify packet drops, jitter, and latency patterns.
Option B) DHCP server misconfiguration would impact IP address allocation but does not selectively introduce latency to VoIP while file transfers remain unaffected. Issues like IP exhaustion or scope misalignment usually manifest as failure to obtain addresses rather than performance degradation.
Option C) VLAN ID mismatch could prevent devices from communicating entirely or create broadcast storms, but this would likely affect all traffic on that VLAN, not selectively VoIP.
Option D) Incorrect console port speed only affects administrative access and device configuration, not live traffic on the network.
In practice, resolving improper QoS requires mapping applications, understanding traffic flows, and defining appropriate policies for prioritization. For example, VoIP traffic could be mapped to EF (Expedited Forwarding) DSCP code points, while bulk file transfers could use AF (Assured Forwarding) or BE (Best Effort). Proper QoS ensures voice packets traverse the WAN with minimal delay, even when other services saturate the link.
Implementing end-to-end QoS is critical. This means configuring policies not only on core and distribution routers but also on access switches, WAN edge devices, and firewalls. Tools like Cisco IP SLA can simulate VoIP traffic and measure delay, jitter, and packet loss, helping validate QoS policies. Proper monitoring helps identify bottlenecks, misconfigurations, or misbehaving applications causing high latency.
In conclusion, when VoIP traffic experiences high latency while other traffic remains stable, the most likely root cause is improper WAN QoS configuration, which can be remediated through proper traffic classification, queue management, and prioritization strategies.
Question 27
Users at a remote office complain that large file transfers over VPN are failing intermittently, but web browsing works normally. What should be examined first?
A) MTU settings along the VPN path
B) DHCP lease times
C) Switch port duplex settings
D) Printer configuration
Answer: A)
Explanation:
When large file transfers fail over a VPN but web browsing works normally, the issue is almost always related to Maximum Transmission Unit (MTU) mismatches along the VPN path. VPNs add extra headers for encapsulation, including IPsec or GRE, which effectively reduce the MTU that can traverse the network without fragmentation.
If packets exceed the allowed MTU and fragmentation is either disabled or blocked by firewalls along the path, packets are silently dropped, resulting in failed file transfers. Smaller, typical web browsing packets do not trigger the issue because they are below the MTU threshold and pass through successfully.
Key steps for troubleshooting MTU issues include:
Identify the effective MTU: Use tools like ping with the “don’t fragment” flag to determine the largest packet size that can traverse the VPN without being dropped.
Adjust MTU settings: Lower the MTU on endpoints, VPN concentrators, or routers to accommodate the extra encapsulation headers. Common practice is to reduce MTU by 50–60 bytes when using IPsec tunnels.
Check intermediate devices: Firewalls, routers, or switches along the path may block ICMP fragmentation-needed messages, preventing endpoints from detecting the proper MTU. Allowing these ICMP messages is critical for path MTU discovery.
Verify fragmentation policies: Some VPN devices can perform fragmentation at the source, while others rely on the network to fragment packets. Misaligned policies can cause intermittent failures during large transfers.
Option B) DHCP lease times control IP allocation and renewal but do not selectively impact large transfers. If DHCP were misconfigured, clients would either fail to obtain IP addresses or lose connectivity entirely, affecting all traffic types.
Option C) Switch port duplex mismatches can cause packet loss or collisions at high speeds, but this would affect all traffic through that switch port, not only large VPN file transfers.
Option D) Printer configuration is unrelated to VPN performance or large file transfers.
A practical example: Consider a remote office with a 1500-byte MTU Ethernet link using an IPsec VPN tunnel. The VPN adds 60 bytes of headers, reducing the effective MTU to 1440 bytes. If the remote client continues to send 1500-byte packets without fragmentation, the VPN traffic will fail, even though smaller HTTP requests succeed. By adjusting the MTU to 1400–1420 bytes, administrators ensure reliable file transfers without affecting smaller packets.
In summary, when VPN file transfers fail intermittently but other traffic works normally, MTU settings along the VPN path should be verified first. Correct MTU alignment prevents dropped packets and ensures smooth performance for latency-sensitive and high-volume traffic alike.
Question 28
After deploying a new wireless controller, users report frequent disconnections, especially in high-density areas. Which configuration should be checked first?
A) Wireless channel and power settings on access points
B) DHCP lease duration
C) VLAN name conventions
D) Switch trunk port labeling
Answer: A)
Explanation:
Frequent wireless disconnections in high-density areas often stem from improper wireless channel planning and power configuration on access points (APs). When multiple APs overlap on the same channel, or if transmit power is too high, clients may constantly roam or experience interference, resulting in dropped connections.
High-density wireless networks are particularly sensitive to channel congestion. Without proper channel separation (e.g., channels 1, 6, 11 in 2.4 GHz), multiple APs can operate on overlapping frequencies, causing co-channel interference. Additionally, excessive transmit power may extend coverage into areas served by neighboring APs, forcing clients to hand off repeatedly.
Steps to troubleshoot include:
Perform a wireless site survey: Identify coverage areas, overlapping APs, and spectrum interference. Tools like Wi-Fi analyzers or controller-based heatmaps provide insight into channel usage and signal strength.
Adjust channel assignments: Configure APs to use non-overlapping channels, and consider dynamic channel assignment features if supported.
Optimize transmit power: Reduce AP power in dense environments to minimize interference and create smaller, more manageable cells.
Check controller settings: Ensure that load balancing and roaming thresholds are configured correctly to prevent unnecessary handoffs.
Option B) DHCP lease duration affects IP allocation but does not directly cause disconnections. Even with short lease times, a client maintains connectivity as long as DHCP renewals succeed.
Option C) VLAN naming conventions are organizational and do not impact wireless performance.
Option D) Switch trunk port labeling is administrative and irrelevant to client connectivity.
Real-world example: A conference room with 50 simultaneous users may have multiple APs transmitting on the same 2.4 GHz channel at maximum power. Users report frequent drops because their devices rapidly switch between APs due to overlapping coverage and signal fluctuations. By reassigning channels and lowering AP power, the wireless network becomes stable, and clients maintain continuous connectivity.
Question 29
Users at a branch office report that their internal applications are extremely slow, but external internet access is fine. What is the most likely cause?
A) WAN link congestion
B) DNS misconfiguration
C) Firewall rule blocking internal traffic
D) Switch STP misconfiguration
Answer: A)
Explanation:
When internal applications are slow while external internet access remains stable, it usually points to WAN link congestion or insufficient bandwidth allocation for internal traffic between the branch and the central office. Many organizations deploy centralized servers for ERP, CRM, or file sharing, which depend heavily on reliable, high-capacity WAN links. If the link becomes saturated during peak hours, internal applications experience latency, slow response times, or even timeouts, whereas external internet services might remain unaffected because traffic routing, caching, or peering arrangements differ.
Key points to investigate:
Bandwidth utilization monitoring: Tools like NetFlow, SNMP-based monitoring, or WAN analytics solutions help identify which applications consume the most bandwidth and when congestion occurs.
Traffic prioritization: WAN traffic may require Quality of Service (QoS) to prioritize business-critical applications over less sensitive data flows like file downloads or streaming. Without QoS, latency-sensitive applications like VoIP or internal ERP systems are disproportionately affected.
Compression or optimization techniques: WAN optimizers, caching, or deduplication devices can reduce the effective traffic load, improving performance for critical applications.
Peak-hour scheduling: Large batch transfers, backups, or updates may need scheduling outside peak business hours to prevent congestion.
Option B) DNS misconfiguration primarily affects name resolution. Users may be unable to reach certain servers or applications but not experience widespread slow performance for all internal apps.
Option C) Firewall rules blocking internal traffic would result in complete application inaccessibility rather than slow performance. Only allowed traffic would reach internal servers, and affected users might experience connection failures instead of delays.
Option D) Switch Spanning Tree Protocol (STP) misconfigurations can cause loops or flooding, potentially slowing traffic, but in most modern switched networks with redundant links, STP issues would affect more than just internal applications. Network-wide symptoms like broadcast storms would appear.
Practical troubleshooting steps include:
Monitoring WAN utilization during different times of day to correlate slowdowns with bandwidth spikes.
Verifying that internal routing paths are optimized, and no bottleneck exists at branch routers or firewalls.
Implementing QoS policies to ensure latency-sensitive traffic is prioritized, such as internal application traffic over bulk file transfers.
Checking for scheduled backups, replication tasks, or software updates that consume disproportionate bandwidth during business hours.
By focusing on WAN link congestion, administrators can identify bottlenecks, apply traffic shaping, and optimize link usage to improve internal application performance without affecting external internet access.
Question 30
Several users complain about intermittent wireless connectivity in a high-density office. What configuration issue is most likely causing the problem?
A) Overlapping wireless channels and excessive transmit power
B) DHCP lease duration
C) Switch port speed mismatch
D) VPN MTU misconfiguration
Answer: A)
Explanation:
Intermittent wireless connectivity in high-density office environments is a common problem caused by overlapping wireless channels and excessive AP transmit power. When multiple access points (APs) operate on the same or overlapping channels, devices experience co-channel interference, which results in packet collisions, retransmissions, and frequent disconnects. Additionally, when transmit power is set too high, AP signals overlap excessively, causing client devices to frequently roam between APs in search of the strongest signal, which leads to further instability.
Steps to troubleshoot and resolve the issue:
Conduct a wireless site survey: Use tools like Wi-Fi analyzers or controller heatmaps to visualize channel usage, signal strength, and coverage overlap. Identify channels with the highest congestion.
Adjust channels appropriately: For the 2.4 GHz spectrum, only non-overlapping channels (1, 6, 11) should be used. In the 5 GHz band, more channels are available, but careful planning is still necessary to prevent interference in high-density deployments.
Optimize transmit power: Reduce AP power to shrink coverage cells and limit overlap, allowing better client distribution across multiple APs. Excessive power can cause devices to stick to one AP too long, leading to degraded throughput and roaming issues.
Enable load balancing and roaming thresholds: Many wireless controllers allow load balancing between APs and set thresholds for signal strength, encouraging devices to connect to the optimal AP rather than bouncing between multiple APs.
Monitor spectrum for interference: Identify sources of RF interference such as microwaves, cordless phones, or neighboring Wi-Fi networks. In high-density environments, interference can exacerbate connectivity problems.
Option B) DHCP lease duration affects IP allocation but rarely causes intermittent connectivity. Even with short lease times, modern clients renew IP addresses seamlessly without dropping connections.
Option C) Switch port speed mismatches create collisions or errors on wired connections but do not directly cause wireless disconnections. They can affect traffic from APs to the wired network, but the symptoms would be more widespread network instability.
Option D) VPN MTU misconfiguration impacts large packets and may disrupt tunneling, but it would not selectively affect wireless connectivity across a high-density office.
Real-world example: In a corporate office with 200 employees using 50 APs, the 2.4 GHz band is fully utilized. Several APs are configured on channel 6 at maximum power. Clients experience frequent disconnections during peak usage. After a site survey, administrators reassign AP channels to minimize overlap and lower transmit power. Additionally, the wireless controller enables band steering, pushing capable devices to 5 GHz, further alleviating congestion. The result is stable wireless connections and improved throughput for all clients.
Question 31
After deploying a new firewall, some internal applications fail to connect externally, while web browsing works normally. What is the likely cause?
A) Incorrect NAT or port forwarding configuration
B) DHCP scope exhaustion
C) VLAN tagging mismatch
D) Wireless SSID misconfiguration
Answer: A)
Explanation:
When internal applications fail to connect externally after deploying a firewall, but web browsing remains functional, the problem is most likely due to incorrect Network Address Translation (NAT) or port forwarding configurations. NAT allows internal devices with private IP addresses to communicate with external networks by translating their addresses to a public IP. Port forwarding allows inbound external connections to reach the correct internal server.
Web browsing works normally because firewalls and NAT devices are typically configured to allow outbound HTTP/HTTPS traffic by default, but specialized applications, such as VoIP, FTP, or custom client-server software, may require specific ports or protocol translations.
Troubleshooting steps:
Check NAT rules: Ensure that all necessary outbound and inbound NAT rules exist for the affected applications. Incorrect NAT may prevent packets from reaching the intended server or returning to the client.
Verify port forwarding: For applications requiring inbound connections, confirm that the firewall forwards traffic to the correct internal server on the right port. Misconfigured ports will cause connection failures.
Inspect firewall policies: Some applications may be blocked by firewall rules even if NAT is correct. Confirm that the firewall allows traffic for the application protocols.
Test connectivity: Tools like telnet, nc (netcat), or application-specific test utilities can confirm if the correct ports are open and reachable externally.
Option B) DHCP scope exhaustion occurs when all IP addresses in a DHCP pool are allocated. While this could prevent devices from obtaining IPs, it would affect connectivity to all networks, not just specific external applications.
Option C) VLAN tagging mismatches can prevent devices from communicating on certain subnets but typically result in complete internal or inter-VLAN communication failures, not selective external connectivity issues.
Option D) Wireless SSID misconfiguration affects wireless connectivity, not wired connections, and would not selectively impact only external application traffic.
Example: A company deploys a firewall in front of its internal servers. Employees can browse websites, but the CRM software fails to sync with the cloud server. Investigation reveals that outbound NAT rules are correctly applied for HTTP/HTTPS traffic but missing for the CRM application’s custom TCP port. Once the firewall rules are updated to include proper NAT and port forwarding for TCP port 5000, the CRM application functions correctly.
Improper NAT or port forwarding configuration is the most common cause of selective application failures after firewall deployment. Ensuring proper translation, forwarding, and policy alignment is crucial for both security and connectivity.
Question 32
A network administrator notices excessive broadcast traffic on a VLAN causing slow performance. Which solution is most effective?
A) Implement VLAN segmentation and limit broadcast domains
B) Reduce DHCP lease time
C) Disable STP on all switches
D) Increase AP transmit power
Answer: A)
Explanation:
Excessive broadcast traffic within a VLAN can severely degrade network performance because every broadcast packet is delivered to all devices in the same broadcast domain. Broadcast storms can saturate links, overwhelm switch CPU resources, and create significant latency. The most effective solution is to implement VLAN segmentation and limit broadcast domains.
Key steps include:
Segment the network into smaller VLANs: Dividing a large VLAN into multiple smaller VLANs reduces the number of devices that receive broadcast traffic, thereby reducing the load on each segment. For example, splitting a 200-user VLAN into four 50-user VLANs limits broadcast exposure.
Implement proper routing: With multiple VLANs, a router or Layer 3 switch is required to route traffic between VLANs, ensuring isolation while allowing necessary communication.
Enable broadcast suppression: Some switches allow broadcast traffic limits per port. Configuring these thresholds can help prevent broadcast storms from affecting the entire VLAN.
Monitor for faulty devices: Excessive broadcast traffic is sometimes caused by misconfigured or failing network devices. Use monitoring tools like SNMP or sFlow to identify sources of high broadcast rates.
Option B) Reducing DHCP lease times has no impact on broadcast traffic beyond the initial DHCP discovery process. It cannot alleviate ongoing broadcast storms caused by normal network traffic.
Option C) Disabling Spanning Tree Protocol (STP) is dangerous and can cause loops, dramatically increasing broadcast traffic. STP exists to prevent these loops and maintain network stability.
Option D) Increasing AP transmit power only extends wireless coverage and can worsen interference in dense environments. It does not address broadcast traffic at the Layer 2 network level.
Practical example: In a corporate office with a single VLAN for all 300 devices, users complain of slow application response times. Network monitoring shows a high volume of broadcast ARP requests and other Layer 2 broadcasts. By splitting the network into six VLANs based on department and applying proper inter-VLAN routing, broadcast traffic is contained within smaller groups, resulting in improved network performance.
Ultimately, VLAN segmentation and limiting broadcast domains is the most effective solution to excessive broadcast traffic, improving network efficiency and reducing latency in high-density environments.
Question 33
Users report intermittent wireless connectivity near a high-powered microwave in the cafeteria. What is the most likely cause?
A) Radio Frequency (RF) interference
B) DHCP lease time expiration
C) NAT misconfiguration
D) Switch port speed mismatch
Answer: A)
Explanation:
When wireless devices experience intermittent connectivity near a microwave oven or other electronic devices, the issue is almost always RF interference. Microwaves operate in the 2.4 GHz frequency range, which overlaps with the commonly used Wi-Fi 2.4 GHz channels. This can cause packet loss, retransmissions, and temporary disconnections.
Troubleshooting steps:
Identify sources of RF interference: Use spectrum analyzers to detect interference in the affected area. Common sources include microwaves, cordless phones, baby monitors, and Bluetooth devices.
Relocate APs or clients: If possible, move access points or affected devices away from the source of interference.
Switch frequency bands: Encourage dual-band devices to use the 5 GHz band, which is less susceptible to common household interference and offers more channels.
Implement channel planning: Avoid using congested channels in the 2.4 GHz range and ensure APs are assigned non-overlapping channels (1, 6, 11).
Use wireless controller features: Many enterprise controllers have interference detection and automatic channel adjustment, which can dynamically mitigate the impact of RF noise.
Option B) DHCP lease expiration has minimal impact because modern clients automatically renew leases before expiration. Intermittent connectivity due to DHCP would be infrequent and typically affect multiple clients simultaneously.
Option C) NAT misconfiguration affects routing between private and public networks, not wireless connectivity near a local interference source.
Option D) Switch port speed mismatches create errors on wired segments but do not directly cause wireless disconnections near interference sources.
Real-world example: In a corporate cafeteria, users report that Wi-Fi drops whenever the microwave is in use. Spectrum analysis confirms significant 2.4 GHz interference. By moving nearby APs slightly away from the microwave and configuring affected users to connect to 5 GHz, connectivity becomes stable. This demonstrates the importance of RF awareness in wireless network design.
RF interference is the primary cause of intermittent wireless connectivity near devices like microwaves, and proper channel planning, AP placement, and band steering are essential for reliable performance.
Question 34
A technician observes that a new Layer 3 switch is dropping packets between VLANs intermittently. Which issue is most likely?
A) Routing table misconfiguration or incomplete routes
B) DNS server misconfiguration
C) Wireless SSID overlap
D) DHCP scope exhaustion
Answer: A)
Explanation:
When a Layer 3 switch intermittently drops packets between VLANs, it is typically caused by routing table misconfiguration or incomplete routes. Layer 3 switches perform inter-VLAN routing by using routing tables to determine the correct path for packets. If a switch has missing routes, incorrect static routes, or misconfigured dynamic routing protocols, packets destined for certain VLANs may be dropped intermittently, particularly if traffic follows inconsistent paths due to network changes or failover conditions.
Troubleshooting steps:
Verify routing tables: Use show ip route or equivalent commands to confirm that all VLANs are present and reachable. Missing entries can explain intermittent connectivity.
Check static routes: If static routes are used, ensure they point to the correct next-hop IP addresses. Typographical errors or misassigned interfaces can disrupt inter-VLAN communication.
Examine dynamic routing protocols: Misconfigured OSPF, EIGRP, or RIP timers can result in temporary route unavailability. Ensure neighbor relationships are stable and routing advertisements propagate correctly.
Test inter-VLAN connectivity: Ping devices in different VLANs while monitoring the routing table for changes. Intermittent failures often reveal timing-related misconfigurations or route flaps.
Option B) DNS misconfigurations affect hostname resolution but do not directly cause packet drops between VLANs, as traffic would still reach devices using IP addresses.
Option C) Wireless SSID overlap affects client connectivity but not routing between VLANs in a wired network.
Option D) DHCP scope exhaustion may prevent some devices from obtaining IP addresses, but it would not explain intermittent packet drops for devices that already have valid addresses.
Practical example: A Layer 3 switch connecting VLANs 10, 20, and 30 intermittently drops traffic between VLAN 10 and 30. Investigation shows that a static route for VLAN 30 points to an incorrect interface. Correcting the route and verifying with ping and traceroute restores stable inter-VLAN connectivity.
In conclusion, routing table misconfigurations or incomplete routes are the primary causes of intermittent Layer 3 packet drops. Ensuring accurate routing tables, static route verification, and proper dynamic routing protocol configuration resolves these issues.
Question 35
Users report slow authentication times when connecting to a new Wi-Fi SSID. What is the most likely cause?
A) RADIUS or authentication server latency
B) DHCP lease expiration
C) VLAN trunk misconfiguration
D) Switch spanning-tree issues
Answer: A)
Explanation:
Slow authentication on a new Wi-Fi SSID is usually caused by RADIUS server or authentication server latency. When using WPA2-Enterprise or WPA3-Enterprise security, wireless clients authenticate via an 802.1X process against a RADIUS server. If the server is under heavy load, misconfigured, or geographically distant, the authentication process can take longer, resulting in delays before users can access the network.
Key troubleshooting steps:
Check RADIUS server performance: Ensure CPU, memory, and network connectivity to the RADIUS server are adequate. High server load can increase authentication times.
Verify authentication configuration: Confirm that the SSID is correctly configured to communicate with the correct RADIUS server and shared secret. Misconfigurations can introduce retries or timeouts.
Inspect network latency: Authentication traffic must traverse the wired network to reach the server. High latency links or routing issues can delay responses.
Enable logging: RADIUS and wireless controllers typically provide logs indicating the time taken for authentication attempts. Analyzing logs can identify server-side delays or misconfigurations.
Evaluate redundancy: If multiple RADIUS servers are in use, ensure failover configuration does not introduce additional delays.
Option B) DHCP lease expiration has little effect on initial authentication. Even if a device must obtain an IP, the DHCP process is usually quick compared to 802.1X authentication delays.
Option C) VLAN trunk misconfiguration can prevent clients from reaching the RADIUS server but would typically result in total authentication failure, not slow authentication.
Option D) Switch spanning-tree issues primarily affect Layer 2 loops and convergence times but are unlikely to cause consistent slow Wi-Fi authentication.
Real-world example: A new corporate SSID is deployed across multiple floors. Users report that connecting takes 20–30 seconds. Investigation shows the RADIUS server is located in the data center and experiences a 50 ms latency per authentication request. Adding a secondary RADIUS server closer to the wireless controller reduces latency to under 2 seconds, resolving the issue.
Question 36
After a recent network upgrade, VoIP calls experience frequent jitter and latency. Which solution will likely improve call quality?
A) Implement Quality of Service (QoS) policies on routers and switches
B) Increase DHCP lease duration for IP phones
C) Disable Spanning Tree Protocol on all switches
D) Move VoIP servers to a separate VLAN without QoS
Answer: A)
Explanation:
When VoIP calls experience jitter, latency, and packet loss, the underlying issue is usually insufficient prioritization of time-sensitive traffic. Voice traffic is sensitive to delay because even small pauses or packet misordering can degrade call quality. Implementing Quality of Service (QoS) on routers and switches is the most effective solution to ensure voice traffic is prioritized over less time-sensitive data.
QoS allows network administrators to classify and prioritize traffic based on type, source, destination, or port. For VoIP, the common approach is to mark voice packets with DSCP (Differentiated Services Code Point) values or assign dedicated VLANs for voice traffic. This ensures that routers and switches handle VoIP packets first, reducing latency and jitter.
Steps for implementing QoS:
Identify voice traffic: Determine the IP ranges or VLANs used by VoIP phones. Most enterprise VoIP solutions also provide specific ports (like UDP 5060 for SIP signaling) that can be classified.
Classify traffic: Configure the switches and routers to recognize and label voice traffic using DSCP or IP precedence.
Prioritize queues: Set up priority queues on routers to ensure voice packets are processed before less critical traffic.
Monitor performance: Use tools like Wireshark or VoIP monitoring software to verify packet loss, jitter, and latency improvements.
Option B) Increasing DHCP lease duration for IP phones has minimal impact on real-time call quality. DHCP only provides IP addressing and does not affect traffic prioritization or latency.
Option C) Disabling Spanning Tree Protocol (STP) can introduce loops, which would increase network congestion and exacerbate latency and jitter problems rather than solving them.
Option D) Moving VoIP servers to a separate VLAN may help with traffic segmentation but without QoS, voice traffic could still compete with data traffic, leading to poor call quality.
Real-world example: A medium-sized enterprise deployed VoIP phones across 150 workstations. Users reported echo, delays, and occasional dropped calls during peak hours. Network monitoring revealed high utilization on core switches with voice packets competing with bulk file transfers. After configuring QoS to prioritize voice traffic using DSCP EF (Expedited Forwarding) and separating voice VLAN traffic, jitter dropped from 30 ms to under 5 ms, and latency improved dramatically, resolving user complaints.
In conclusion, QoS implementation is critical for ensuring reliable and high-quality VoIP communication. Prioritizing time-sensitive traffic, combined with proper network monitoring and traffic classification, reduces jitter, latency, and packet loss, creating a robust environment for voice services.
Question 37
A new wireless deployment shows frequent client disconnections near certain APs. Which factor is most likely causing this issue?
A) Channel interference or overlapping wireless channels
B) DHCP server misconfiguration
C) Incorrect VLAN trunking on switches
D) NAT misconfiguration on the firewall
Answer: A)
Explanation:
Frequent wireless client disconnections are often caused by channel interference or overlapping wireless channels. In the 2.4 GHz band, only three non-overlapping channels (1, 6, 11) exist. Placing APs too close or on overlapping channels leads to co-channel interference, reducing throughput and causing clients to disconnect. The 5 GHz band offers more channels, but interference can still occur from other APs, Bluetooth devices, or electronic equipment.
Steps to resolve wireless interference:
Conduct a site survey: Use tools such as spectrum analyzers or Wi-Fi scanning apps to identify channel utilization and interference sources.
Reassign channels: For the 2.4 GHz band, use non-overlapping channels 1, 6, and 11. For 5 GHz, choose channels that are not congested.
Adjust AP placement: Avoid placing APs too close to other wireless devices, microwaves, or metal objects that can reflect or absorb signals.
Lower transmit power: High transmit power may cause clients to associate with distant APs, resulting in weak signal quality. Proper tuning ensures clients connect to the nearest AP.
Enable band steering: Encourage dual-band clients to use 5 GHz to reduce 2.4 GHz congestion.
Option B) DHCP misconfiguration would prevent clients from obtaining IP addresses entirely, but wouldn’t typically cause intermittent disconnects.
Option C) Incorrect VLAN trunking affects network access for specific VLAN traffic but does not inherently cause clients to disconnect frequently.
Option D) NAT misconfiguration affects routing between private and public networks but does not cause Wi-Fi clients to drop their connection to an AP.
Example: A university campus deployed 50 APs in overlapping 2.4 GHz channels to cover dormitories. Students reported frequent Wi-Fi drops. A site survey revealed heavy co-channel interference. Adjusting channels to 1, 6, 11, and shifting high-density areas to 5 GHz reduced disconnects by 80%, demonstrating the importance of careful channel planning and interference mitigation in wireless design.
In conclusion, channel interference or overlapping channels is the most common cause of intermittent wireless client disconnects. Proper channel planning, AP placement, and monitoring tools are essential to ensure reliable wireless connectivity.
Question 38
After a router upgrade, some remote users cannot establish VPN connections. Which configuration issue is the most probable cause?
A) Missing or incorrect firewall VPN rules
B) Expired DHCP lease for remote clients
C) Wireless SSID misconfiguration
D) Switch port duplex mismatch
Answer: A)
Explanation:
When VPN connections fail after a router upgrade, the issue is usually due to missing or incorrect firewall rules that block VPN traffic. VPN protocols such as IPsec, L2TP, or SSL require specific ports and protocols to traverse the firewall. If rules allowing inbound VPN traffic to the router are absent or misconfigured, clients cannot establish tunnels.
Troubleshooting steps:
Verify firewall rules: Ensure that UDP 500 (IKE), UDP 4500 (NAT-T), and ESP (IP protocol 50) are allowed for IPsec VPNs. For SSL VPNs, confirm that TCP 443 is open.
Check VPN configuration: Ensure the router’s VPN service is enabled and configured correctly with the right subnet, authentication, and encryption parameters.
Test connectivity: Use tools such as ping, traceroute, or packet capture to verify if VPN packets reach the router and responses return.
Validate NAT policies: NAT or PAT misconfigurations can block VPN traffic if not properly accounted for in the firewall.
Option B) Expired DHCP leases do not prevent VPN establishment for remote users with static or renewed IP addresses.
Option C) Wireless SSID misconfigurations affect local Wi-Fi clients, not remote VPN users connecting over the internet.
Option D) Switch port duplex mismatches affect local wired network performance but do not prevent remote VPN connections.
Example: After upgrading a small office router, employees could no longer connect via IPsec VPN. Examination revealed that the upgrade reset firewall settings, removing rules for UDP 500 and UDP 4500. Once the firewall was updated to allow the necessary ports, VPN connections were restored, confirming the firewall misconfiguration as the root cause.
In conclusion, firewall VPN rules must be carefully reviewed after any router or firewall upgrade to ensure remote VPN connectivity is preserved. This is critical for maintaining secure access for remote users.
Question 39
A network monitoring tool reports high CPU usage on a core switch during peak hours. What is the most likely cause?
A) Excessive broadcast or multicast traffic overwhelming the switch CPU
B) DHCP scope exhaustion
C) VLAN trunk misconfiguration
D) Incorrect NAT settings
Answer: A)
Explanation:
High CPU usage on core switches is often caused by excessive broadcast or multicast traffic. Switch CPUs are responsible for processing Layer 3 functions, management traffic, spanning tree calculations, and certain control-plane activities. When broadcast or multicast storms occur, each frame must be processed by the CPU for forwarding decisions, ACL checks, or spanning tree recalculations, leading to elevated CPU usage.
Steps to identify and resolve high CPU usage:
Monitor traffic patterns: Use SNMP, NetFlow, or sFlow to identify unusual broadcast or multicast spikes. Look for patterns during peak hours.
Implement VLAN segmentation: Divide large broadcast domains into smaller VLANs to limit the number of devices affected by broadcast traffic.
Enable broadcast suppression: Many enterprise switches allow broadcast or multicast storm control, limiting the percentage of traffic to CPU.
Review network loops: Ensure Spanning Tree Protocol is functioning correctly. Loops can generate exponential broadcast traffic, overloading the switch CPU.
Check for misbehaving devices: Endpoints or misconfigured servers can generate excessive ARP requests, multicast traffic, or network storms. Identify and remediate these devices.
Option B) DHCP scope exhaustion affects address assignment but does not directly cause CPU spikes unless DHCP requests are unusually high and overwhelming the server.
Option C) VLAN trunk misconfiguration can cause connectivity issues but rarely results in high CPU unless it triggers broadcast storms.
Option D) NAT misconfiguration affects traffic translation for outbound connections but does not overload a switch CPU in typical LAN scenarios.
Example: A financial institution observed CPU utilization spikes on its core switch during mid-day transaction processing. Investigation showed that a misconfigured printer was flooding the network with multicast service discovery packets. Enabling multicast storm control on affected ports and moving the printer to a separate VLAN reduced CPU usage and restored normal switch performance.
In conclusion, broadcast or multicast traffic is the primary cause of high CPU utilization on core switches. Proper traffic segmentation, storm control, and monitoring tools are crucial to maintaining network stability and performance.
Question 40
After implementing a new Layer 2 switch, users report slow file transfers and occasional disconnects. What is the most likely cause?
A) Duplex mismatch between the switch and end devices
B) DHCP server misconfiguration
C) Firewall blocking port 80 traffic
D) RADIUS authentication delays
Answer: A)
Explanation:
Slow file transfers and intermittent connectivity after deploying a new switch are often caused by a duplex mismatch. Duplex settings define whether a network interface can send and receive data simultaneously (full-duplex) or one direction at a time (half-duplex). Mismatches between switch ports and end devices cause collisions, retransmissions, and reduced throughput, leading to slow file transfers and occasional disconnects.
Steps to identify and resolve duplex mismatches:
Check interface statistics: Examine switch port counters for collisions, late collisions, or CRC errors, which are indicators of duplex mismatches.
Verify end device settings: Ensure that NICs on computers, servers, and printers match the switch port duplex settings. Modern devices typically use auto-negotiation.
Enable auto-negotiation carefully: While auto-negotiation usually resolves duplex conflicts, some older devices may require manual configuration. Ensure consistency across the network.
Test throughput: Conduct file transfer tests and monitor for errors after correcting duplex mismatches to ensure performance restoration.
Option B) DHCP misconfiguration can prevent devices from receiving IP addresses but would not cause intermittent connectivity after IP assignment.
Option C) Firewall blocking port 80 affects web traffic, not general file transfers within a LAN.
Option D) RADIUS authentication delays affect network access control but would not cause sustained throughput problems or repeated disconnects for already authenticated users.
Example: A corporate office installed a new Layer 2 switch for a department. Users noticed slow SMB file transfers and occasional disconnections. Switch monitoring revealed repeated collisions on multiple ports. Examination showed the switch ports were set to full-duplex while some PCs were defaulting to half-duplex. Correcting the port settings and enabling consistent auto-negotiation eliminated collisions and restored normal transfer speeds.
