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Question 41:
Which OSPF LSA type is used to advertise routes between areas in an OSPF domain?
Type 1 – Router LSA
B. Type 2 – Network LSA
C. Type 3 – Summary LSA
D. Type 5 – AS External LSA
Answer: C. Type 3 – Summary LSA
Explanation:
Type 3 LSAs are generated by Area Border Routers (ABRs) to summarize routes between OSPF areas. They enable efficient routing without flooding all internal LSAs from one area into another. Type 1 LSAs describe routers within an area, Type 2 LSAs describe broadcast networks, and Type 5 LSAs advertise external routes into OSPF. Understanding LSAs is crucial for troubleshooting inter-area OSPF routing and avoiding unnecessary flooding. In OSPF (Open Shortest Path First), Link-State Advertisements (LSAs) are the fundamental mechanism by which routers share topology information. Each LSA type serves a specific purpose in enabling efficient and scalable routing.
Type 1 – Router LSA: Type 1 LSAs are generated by every router within an OSPF area to describe itself and its directly connected links. These LSAs contain information such as the router ID, link types (point-to-point, broadcast, etc.), and metrics. They are confined to the area in which they originate, ensuring that routers in the same area have an identical view of the local topology. Understanding Type 1 LSAs is essential for troubleshooting internal area connectivity issues.
Type 2 – Network LSA: Type 2 LSAs are generated by the designated router (DR) on a broadcast or non-broadcast multi-access network. They describe all routers attached to the network, effectively representing the network as a single logical node. Type 2 LSAs are crucial for routers within the same area to understand the shared network topology and correctly calculate shortest-path routes.
Type 3 – Summary LSA: Type 3 LSAs are created by Area Border Routers (ABRs) to summarize routes between OSPF areas. By propagating Type 3 LSAs, ABRs allow routers in one area to learn about networks in another area without flooding all Type 1 or Type 2 LSAs. This summarization reduces routing table size and limits unnecessary LSA flooding, making OSPF more scalable.
Type 5 – AS External LSA: Type 5 LSAs advertise routes from external autonomous systems into the OSPF domain. These LSAs are generated by autonomous system boundary routers (ASBRs) and are flooded throughout the OSPF domain, except into stub areas. They enable OSPF routers to reach networks outside the OSPF domain.
Understanding the purpose and scope of these LSA types is crucial for designing OSPF topologies, optimizing routing efficiency, and troubleshooting inter-area or external routing issues. Proper LSA management ensures minimal overhead and accurate network reachability information.
Question 42:
Which QoS tool drops traffic that exceeds a configured rate immediately?
Traffic Shaping
B. Policing
C. LLQ
D. CBWFQ
Answer: B. Policing
Explanation:
Traffic policing enforces a maximum rate by dropping or remarking packets that exceed the configured bandwidth. Unlike shaping, which buffers excess traffic, policing enforces strict limits immediately. CBWFQ and LLQ manage queues but do not perform rate enforcement at the ingress. Policing is often used at network edges to enforce service-level agreements (SLAs) or ISP contracts. In networking, traffic management mechanisms are crucial for ensuring efficient bandwidth utilization, minimizing congestion, and maintaining service quality. The four techniques listed—Traffic Shaping, Policing, LLQ, and CBWFQ—serve different purposes in controlling traffic flow.
Traffic Shaping: Traffic shaping is a QoS technique that regulates the flow of outbound traffic by buffering excess packets and sending them at a controlled rate. Unlike policing, shaping smooths traffic bursts rather than dropping packets, which helps prevent packet loss during congestion. It is often used in environments where consistent bandwidth usage is necessary, such as WAN links or enterprise-to-ISP connections. By delaying packets instead of discarding them, shaping improves overall network performance and reduces retransmissions caused by packet drops.
Policing: Traffic policing enforces a strict maximum rate for traffic entering the network. Packets that exceed the configured bandwidth can either be dropped or marked with a lower priority. Policing does not buffer excess traffic; it immediately enforces the limit. This makes it suitable for enforcing service-level agreements (SLAs) or ISP contracts where exceeding a committed rate is not allowed. Policing is often applied at network edges to control customer traffic or prevent misuse of shared resources.
Low Latency Queuing (LLQ): LLQ is an extension of Class-Based Weighted Fair Queuing (CBWFQ) that adds strict priority queuing for delay-sensitive traffic, such as voice or video. It ensures that critical traffic is transmitted before other classes, reducing latency and jitter. Unlike shaping or policing, LLQ does not directly enforce bandwidth limits; instead, it prioritizes traffic within a queue structure.
Class-Based Weighted Fair Queuing (CBWFQ): CBWFQ divides traffic into classes based on policies and allocates bandwidth proportionally to each class. While it ensures fair bandwidth distribution and prevents starvation, CBWFQ does not enforce strict rate limits or provide strict priority for delay-sensitive traffic like LLQ.
Understanding the differences between shaping, policing, and queue management techniques is essential for designing QoS policies that balance fairness, efficiency, and performance for various types of network traffic.
Question 43:
Which Cisco wireless feature allows a lightweight AP to switch locally in case the controller becomes unreachable?
FlexConnect
B. CAPWAP
C. LWAPP
D. Rogue Detection
Answer: A. FlexConnect
Explanation:
FlexConnect enables lightweight APs to switch traffic locally instead of tunneling everything to the wireless controller via CAPWAP. This allows continued network access if the controller becomes unavailable. LWAPP is the older protocol replaced by CAPWAP, which primarily tunnels traffic back to the controller. Rogue Detection monitors unauthorized devices but does not provide local switching. FlexConnect is essential for branch deployments and high-availability scenarios. In Cisco wireless networks, understanding the different deployment modes and protocols for Access Points (APs) is crucial for ensuring efficient traffic handling, high availability, and security. The four concepts—FlexConnect, CAPWAP, LWAPP, and Rogue Detection—serve different purposes in managing wireless traffic and network performance.
FlexConnect: FlexConnect is a deployment mode for lightweight APs that allows them to locally switch client traffic at the branch site instead of tunneling it all back to a central wireless controller via CAPWAP. This local switching capability is critical in branch or remote deployments where bandwidth to the controller may be limited. Additionally, FlexConnect supports client authentication, VLAN assignment, and QoS policies locally, which allows continued network access even if the connection to the controller is lost. This makes FlexConnect highly valuable for high-availability scenarios and distributed networks.
CAPWAP (Control and Provisioning of Wireless Access Points): CAPWAP is the standard protocol used to manage lightweight APs by tunneling control and data traffic between the AP and the wireless controller. It centralizes management, simplifies policy enforcement, and provides a secure communication channel between the AP and controller. Unlike FlexConnect, CAPWAP requires client traffic to traverse the tunnel to the controller unless local switching is enabled, which can increase WAN bandwidth usage in branch deployments.
LWAPP (Lightweight Access Point Protocol): LWAPP is the legacy protocol that preceded CAPWAP. It also tunnels traffic between APs and the controller, but has been largely replaced by CAPWAP due to CAPWAP’s enhanced features, standardization, and improved security.
Rogue Detection: Rogue Detection is a security mechanism used by APs and controllers to identify unauthorized or rogue devices within the wireless environment. While essential for network security, rogue detection does not provide traffic switching or tunneling capabilities. It is a monitoring function rather than a traffic-handling feature.
Understanding these four mechanisms helps network engineers design wireless deployments that balance central management, local traffic handling, high availability, and security. FlexConnect, in particular, provides flexibility and resilience for branch networks, while CAPWAP ensures centralized control, and rogue detection maintains security.
Question 44:
Which BGP attribute is used to prefer an exit point for outgoing traffic within the same AS?
Local Preference
B. MED
C. AS Path
D. Community
Answer: A. Local Preference
Explanation:
Local Preference is a well-known discretionary attribute in BGP used within an AS to select the preferred exit point for outbound traffic. Higher Local Preference values are preferred. MED is used to influence inbound traffic from another AS. AS Path prevents loops, and Community allows grouping of routes for policy application. Correct configuration of Local Preference ensures optimal routing for internal traffic. In BGP (Border Gateway Protocol), path selection is determined by a combination of attributes that influence routing decisions within and between Autonomous Systems (ASes). Understanding these attributes—Local Preference, MED, AS Path, and Community—is essential for designing efficient routing policies and ensuring optimal traffic flow.
Local Preference: Local Preference is a well-known discretionary BGP attribute used to influence outbound traffic within a single AS. Routers use Local Preference to determine the preferred exit point when multiple paths to an external destination exist. Higher Local Preference values are preferred over lower ones. For example, if a network has two connections to the same external AS, the path with a higher Local Preference will be selected for outbound traffic. Properly configuring Local Preference ensures traffic leaves the AS along the most optimal path, improving performance and policy compliance.
MED (Multi-Exit Discriminator): MED is an optional, non-transitive BGP attribute that influences inbound traffic from a neighboring AS. It allows an AS to indicate to external peers which entry point is preferred. Unlike Local Preference, which affects internal routing decisions, MED is shared with external BGP neighbors to suggest preferred ingress points. Lower MED values are preferred. MED is useful when multiple connections exist between two ASes, helping control how other networks send traffic into your AS.
AS Path: The AS Path is a mandatory attribute that lists all ASes a route has traversed. It serves two main purposes: loop prevention and route selection. BGP prefers the shortest AS Path, ensuring that traffic takes the shortest path in terms of AS hops. The AS Path is also critical for avoiding routing loops in complex networks.
Community: The Community attribute is an optional, transitive attribute used to group routes and apply routing policies efficiently. Network operators can assign communities to routes and then match them in policy rules, enabling actions such as route filtering, redistribution, or Local Preference adjustments. Communities simplify large-scale BGP policy management.
Correct understanding and configuration of these attributes allow network engineers to control inbound and outbound traffic effectively, optimize performance, enforce policies, and maintain stable, loop-free BGP routing across large networks.
Question 45:
Which MPLS feature allows traffic to follow a specific pre-defined path for engineering purposes?
LDP
B. RSVP-TE
C. ARP
D. NAT
Answer: B. RSVP-TE
Explanation:
RSVP-TE (Resource Reservation Protocol-Traffic Engineering) establishes explicit LSPs for MPLS traffic engineering, ensuring that traffic follows a specific path with guaranteed bandwidth. LDP assigns labels dynamically along shortest paths but does not allow explicit path control. ARP resolves MAC addresses, and NAT translates IP addresses; neither is involved in MPLS path engineering. RSVP-TE is widely used in service provider networks for QoS-sensitive traffic. In MPLS (Multiprotocol Label Switching) networks, controlling the path that traffic takes and ensuring quality of service (QoS) is essential, especially for service providers handling delay-sensitive applications. Several protocols and mechanisms are involved in forwarding and managing traffic, but only some are relevant for traffic engineering and path control.
LDP (Label Distribution Protocol): LDP is used in MPLS networks to dynamically assign labels to routes along the shortest-path routing determined by the IGP (Interior Gateway Protocol). While LDP simplifies label distribution and supports basic MPLS forwarding, it does not provide explicit control over the path that traffic follows. Traffic always takes the IGP-calculated shortest path, making LDP suitable for general MPLS forwarding but not for traffic engineering scenarios where precise path selection is required.
RSVP-TE (Resource Reservation Protocol-Traffic Engineering): RSVP-TE extends RSVP to support MPLS traffic engineering by allowing the establishment of explicit Label Switched Paths (LSPs). Network operators can specify constraints such as bandwidth, administrative weight, or path avoidance to route traffic along a specific path. This ensures that critical traffic receives the required QoS and that the network can efficiently utilize resources. RSVP-TE is widely deployed in service provider networks to guarantee bandwidth for delay-sensitive traffic such as VoIP, video conferencing, or real-time data streams.
ARP (Address Resolution Protocol): ARP is a protocol used to map IP addresses to MAC addresses within a local network segment. While essential for basic IP-to-Ethernet communication, ARP plays no role in MPLS label distribution or traffic engineering.
NAT (Network Address Translation): NAT modifies IP address information in packet headers to allow communication between private and public networks or to conserve IP addresses. Like ARP, NAT does not influence MPLS path selection or QoS.
In summary, while LDP provides automatic label assignment for standard MPLS forwarding, RSVP-TE is the key protocol for traffic engineering, enabling explicit path control and bandwidth guarantees. ARP and NAT are unrelated to MPLS path engineering but serve critical functions in basic IP network operations.
Question 46:
Which command verifies the current HSRP state and priority on a Cisco router?
show standby
B. show ip route
C. show running-config
D. show interfaces
Answer: A. show standby
Explanation:
The show standby command displays HSRP group information, including active and standby routers, priority, timers, and virtual IP addresses. This is essential for troubleshooting gateway redundancy. Show ip route shows routing entries, show running-config shows the configuration, and show interfaces displays interface status, but none provide HSRP-specific information. Proper verification ensures high availability for hosts in the network. The show standby command is specifically used to display HSRP (Hot Standby Router Protocol) information, including the active and standby routers, priorities, timers, and the virtual IP address. This is crucial for verifying and troubleshooting gateway redundancy in a network to ensure high availability for hosts. In contrast, show ip route displays routing table entries, show running-config reveals the current device configuration, and show interfaces provides interface status and statistics. While these commands are useful for general network troubleshooting, only the show standby command provides HSRP-specific details necessary to confirm proper failover and redundancy behavior.
Question 47:
Which Cisco technology allows multiple virtual networks to share the same physical infrastructure securely?
VLAN
B. VXLAN
C. STP
D. EtherChannel
Answer: B. VXLAN
Explanation:
VXLAN (Virtual Extensible LAN) encapsulates Layer 2 traffic over Layer 3 networks, allowing multiple isolated virtual networks to share the same physical network infrastructure. VLANs provide basic Layer 2 segmentation but are limited in scale (4096 VLANs). STP prevents loops in Ethernet networks, and EtherChannel aggregates physical links. VXLAN is critical for data center network virtualization and cloud-scale deployments.VXLAN (Virtual Extensible LAN) enables Layer 2 traffic to be encapsulated over Layer 3 networks, allowing multiple isolated virtual networks to coexist on the same physical infrastructure. This overcomes the scalability limitations of traditional VLANs, which support only up to 4096 IDs. STP (Spanning Tree Protocol) prevents Layer 2 loops but does not provide network virtualization. EtherChannel aggregates multiple physical links to increase bandwidth and provide redundancy, but does not create isolated networks. VXLAN is therefore essential for modern data center virtualization and cloud-scale deployments, enabling large-scale multi-tenant networks with efficient Layer 2 connectivity over Layer 3.
Question 48:
Which EIGRP metric component primarily reflects link bandwidth?
Delay
B. Bandwidth
C. Load
D. Reliability
Answer: B. Bandwidth
Explanation:
EIGRP uses a composite metric based on bandwidth, delay, reliability, and load, with bandwidth being the primary factor affecting path selection. Lower bandwidth increases the metric, making paths less preferred. Delay measures latency, reliability indicates link stability, and load reflects current utilization. Understanding these components is critical for tuning EIGRP metrics and ensuring optimal routing.
EIGRP (Enhanced Interior Gateway Routing Protocol) uses a composite metric to determine the best path to a destination, taking into account bandwidth, delay, reliability, and load. Each of these factors influences how the routing protocol evaluates multiple paths, allowing network engineers to optimize routing decisions.
Bandwidth is the primary factor in EIGRP’s metric calculation. It reflects the slowest link along a path, with lower bandwidth links increasing the metric value and making a route less preferred. Ensuring accurate bandwidth configuration on interfaces is crucial because it heavily affects path selection.
Delay measures the cumulative latency of a path, considering the time required for packets to traverse each link. Higher delays increase the metric, signaling less desirable paths. Delay is particularly important in networks with high-latency links or mixed media types.
Reliability represents the stability and error rate of a link. Links with frequent failures or high error rates reduce reliability, increasing the EIGRP metric. Monitoring and adjusting for reliability ensures that traffic avoids unstable links.
Load reflects the current utilization of a link. Heavily loaded links contribute to a higher metric, guiding EIGRP to prefer less congested paths. This dynamic factor helps balance traffic across multiple paths in real-time.
Understanding these four components allows network administrators to fine-tune EIGRP metrics, optimize routing, and maintain high network performance and reliability across complex topologies.
Question 49:
Which wireless security protocol protects against dictionary attacks using dynamic keys per session?
WPA2-PSK
B. WPA2-Enterprise
C. WEP
D. Open Authentication
Answer: B. WPA2-Enterprise
Explanation:
WPA2-Enterprise uses 802.1X with RADIUS authentication to assign unique, per-session encryption keys, mitigating risks from dictionary or replay attacks. WPA2-PSK uses a static pre-shared key, vulnerable if the key is compromised. WEP is deprecated and insecure, while open authentication offers no encryption or security. WPA2-Enterprise is standard for enterprise networks requiring strong access control and encryption. Wireless networks rely on security protocols to protect data confidentiality, integrity, and access control. Among the options listed, WPA2-Enterprise, WPA2-PSK, WEP, and Open Authentication, only WPA2-Enterprise provides robust, scalable security suitable for enterprise environments.
WPA2-Enterprise uses 802.1X authentication in conjunction with a RADIUS server to provide unique, per-session encryption keys for each user or device. This mitigates risks from dictionary, replay, and key reuse attacks, ensuring that even if one session key is compromised, others remain secure. It is the preferred standard in enterprise networks where strong authentication and centralized access control are required.
WPA2-PSK relies on a single pre-shared key for all users. While it provides AES-based encryption similar to WPA2-Enterprise, its security is limited because the key is static. If an attacker obtains the PSK, the entire network is compromised.
WEP is an outdated protocol with well-known vulnerabilities in its encryption algorithm, making it easily breakable with modern tools. It is considered insecure and unsuitable for any network.
Open Authentication provides no encryption or authentication, leaving the network completely exposed to unauthorized access and eavesdropping.
Understanding these differences is crucial for designing secure wireless networks. WPA2-Enterprise balances strong encryption with user-specific authentication, making it the standard choice for enterprises that require both security and manageability.
Question 50:
Which Cisco feature allows traffic classification based on IP, protocol, or application for QoS purposes?
MQC (Modular QoS CLI)
B. Port Security
C. STP
D. EtherChannel
Answer: A. MQC (Modular QoS CLI)
Explanation:
MQC provides a structured method to classify traffic with class maps, define policies with policy maps, and apply them with service policies. Traffic can be matched using IP addresses, protocol types, DSCP markings, or application-specific parameters. Port Security restricts MAC addresses, STP prevents loops, and EtherChannel aggregates links. MQC is the foundational mechanism for implementing advanced QoS in enterprise and service provider networks. Modular QoS CLI (MQC) provides a structured framework to implement advanced Quality of Service (QoS) by allowing traffic classification with class maps, defining policies with policy maps, and applying them via service policies. Traffic can be matched based on IP addresses, protocols, DSCP values, or applications, enabling precise control over bandwidth, priority, and queueing. In contrast, Port Security restricts MAC addresses on interfaces, STP prevents Layer 2 loops, and EtherChannel aggregates multiple links for increased bandwidth and redundancy. MQC is therefore essential for shaping, policing, and prioritizing traffic in enterprise and service provider networks.
Question 51:
Which command verifies MPLS label bindings on a router?
show mpls forwarding-table
B. show ip route
C. show interfaces
D. show running-config
Answer: A. show mpls forwarding-table
Explanation:
The show mpls forwarding-table command displays the labels assigned to FECs (Forwarding Equivalence Classes), next hops, and outgoing interfaces. This is essential for troubleshooting MPLS LSPs. Show ip route shows routed paths, show interfaces shows interface status, and show running-config displays configuration, but none provide detailed MPLS label information. Proper verification ensures traffic is forwarded along the correct LSP. In MPLS (Multiprotocol Label Switching) networks, verifying that traffic is properly forwarded along Label Switched Paths (LSPs) is critical. Cisco routers provide several commands for network visibility, but only specific ones give detailed MPLS forwarding information.
show mpls forwarding-table: This command is essential for troubleshooting MPLS because it displays the label forwarding information for all FECs (Forwarding Equivalence Classes). The output includes the incoming label, outgoing label, next-hop IP address, and outgoing interface. By examining the MPLS forwarding table, network engineers can confirm that packets are being correctly mapped to LSPs and ensure traffic follows the intended path. It is particularly useful for verifying LDP or RSVP-TE label assignments and detecting misconfigurations in label distribution or path setup.
show ip route: This command displays the routing table and shows all routes learned via routing protocols. While it indicates the next-hop IP addresses for destinations, it does not provide MPLS-specific label information. It is useful for general connectivity troubleshooting, but cannot verify MPLS LSP operation.
show interfaces: This command provides the operational status, statistics, and errors for router interfaces. It helps identify physical or data-link issues, such as interface flaps or high error rates, but does not give information about MPLS labels or LSPs.
show running-config: This command displays the device’s current configuration, including MPLS-related settings, routing protocols, and interface configurations. While it helps verify that MPLS is configured, it does not provide dynamic label assignments or forwarding paths.
Question 52:
Which HSRP configuration parameter determines which router becomes active?
Priority
B. Virtual IP
C. Hello Interval
D. Authentication
Answer: A. Priority
Explanation:
HSRP uses the priority value to elect the active router. The router with the highest priority becomes active, while the next highest becomes standby. Virtual IP addresses define the shared gateway, Hello intervals control timer messages, and authentication secures HSRP messages. Correct priority configuration ensures predictable failover behavior and high availability.HSRP (Hot Standby Router Protocol) is a Cisco redundancy protocol that ensures high availability for hosts by providing a virtual default gateway. Several parameters control HSRP operation, with priority, virtual IP, Hello interval, and authentication being key components.
Priority is the most important factor in determining which router becomes the active HSRP router. The router with the highest priority value is elected as active, while the router with the next highest priority becomes the standby. Proper configuration of priority ensures predictable failover behavior and prevents unintended routers from taking over as active.
Virtual IP defines the shared gateway address used by hosts in the subnet. Both the active and standby routers monitor this IP, and the active router responds to traffic destined for it. This allows seamless failover without requiring any changes to host configurations.
Hello Interval specifies the frequency at which HSRP routers send Hello messages to detect the status of peers. Shorter intervals can improve failover responsiveness but may increase protocol overhead.
Authentication provides security by verifying HSRP messages between routers, preventing unauthorized devices from influencing router elections or taking over the virtual IP.
Understanding and correctly configuring these four parameters ensures that HSRP provides reliable gateway redundancy, predictable active/standby roles, and secure operation, which are critical for maintaining network uptime and minimizing disruptions.
Question 53:
Which command verifies the EIGRP neighbor adjacency?
show ip eigrp neighbors
B. show ip route
C. show ip protocols
D. show running-config
Answer: A. show ip eigrp neighbors
Explanation:
The show ip eigrp neighbors command displays EIGRP neighbor relationships, including IP addresses, interface, hold time, and uptime. This is key for verifying adjacency formation and troubleshooting missing neighbors. Show ip route shows the routing table, show ip protocols displays protocol parameters, and show running-config shows the configuration, but these commands do not provide real-time neighbor information. In EIGRP (Enhanced Interior Gateway Routing Protocol), verifying neighbor relationships is fundamental to ensuring stable routing and connectivity. Cisco provides several commands to monitor EIGRP, but each serves a different purpose. Understanding the distinction between them helps network engineers effectively troubleshoot and optimize EIGRP operations.
show ip eigrp neighbors: This command is essential for monitoring EIGRP neighbor relationships. It displays the list of neighbors with which the router has successfully formed adjacencies, including details such as neighbor IP addresses, the interface through which the neighbor is reachable, hold time, uptime, and sequence numbers. By examining this output, engineers can verify that all intended EIGRP neighbors are established and operating correctly. If a neighbor is missing, the command helps identify potential issues with interfaces, routing configurations, or authentication mismatches. This makes show ip eigrp neighbors the primary tool for adjacency troubleshooting.
show ip route: This command displays the routing table, including routes learned via EIGRP. While it confirms that routes are being installed in the routing table, it does not provide real-time information about neighbor formation or adjacency status. It is useful for verifying route propagation, but it cannot directly diagnose missing neighbor issues.
show ip protocols: This command provides general information about the EIGRP process, including autonomous system number, timers, and networks being advertised. While helpful for understanding protocol parameters, it does not reveal the status of individual neighbor relationships or real-time adjacency information.
show running-config: This command shows the current router configuration, including EIGRP network statements and interface settings. It is useful for verifying that the correct configuration is applibut it it does not reflect dynamic neighbor states or operational issues.
Question 54:
Which BGP feature reduces the number of iBGP peerings required in a full-mesh topology?
Route Reflector
B. Confederation
C. Local Preference
D. AS Path
Answer: A. Route Reflector
Explanation:
Route Reflectors (RRs) allow iBGP routers to advertise routes without requiring a full-mesh of peerings, reducing configuration complexity. Confederations split an AS into sub-ASes but still require iBGP connections within each sub-AS. Local Preference influences path selection, and AS Path prevents loops. Using RRs simplifies iBGP scalability in large enterprise or service provider networks. In BGP (Border Gateway Protocol), scaling iBGP within large autonomous systems (AS) can be challenging due to the requirement for a full-mesh of peerings. Route Reflectors (RRs) and Confederations are two mechanisms designed to reduce this complexity, while attributes like Local Preference and AS Path influence routing decisions.
Route Reflectors allow iBGP routers to advertise routes to other iBGP peers without requiring a direct peering with every router in the AS. An RR receives route updates from client routers and reflects them to other clients or non-clients. This significantly reduces the number of iBGP sessions needed, simplifying configuration and improving scalability in large enterprise or service provider networks.
Confederations split a single AS into multiple sub-ASes, where each sub-AS behaves like a smaller AS internally. iBGP full-mesh is required within each sub-AS, but external peering between sub-ASes is simplified. This approach also helps manage large iBGP deployments, but requires more administrative planning compared to RRs.
Local Preference is a well-known BGP attribute used to influence outbound path selection within an AS. Higher values are preferred, allowing administrators to control which exit point traffic uses.
AS Path is a mandatory attribute listing all ASes a route has traversed. It helps prevent loops and allows BGP to prefer paths with fewer AS hops.
Combining RRs with proper Local Preference and AS Path understanding enables efficient, scalable, and loop-free BGP deployments in large networks.
Question 55:
Which MPLS forwarding mechanism replaces IP lookups with label lookups?
Label Switching
B. ARP
C. NAT
D. DHCP
Answer: A. Label Switching
Explanation:
MPLS forwards packets using label switching instead of IP routing lookups. The router examines the incoming label, swaps it according to the forwarding table, and forwards it to the next hop. ARP resolves MAC addresses, NAT translates addresses, and DHCP assigns IP addresses. Label switching improves forwarding speed and supports traffic engineering.MPLS (Multiprotocol Label Switching) is a high-performance forwarding technology that improves the efficiency and flexibility of packet transport in modern networks. The key distinction of MPLS is label switching, which differs from traditional IP routing and allows for faster, more predictable packet forwarding.
Label Switching: In MPLS, packets are assigned a short, fixed-length label when they enter the network. Routers, known as Label Switch Routers (LSRs), examine the incoming label and make forwarding decisions based on a pre-established label forwarding table. The LSR swaps the incoming label with an outgoing label and forwards the packet to the next hop along a predetermined Label Switched Path (LSP). This eliminates the need for each router to perform a full IP routing table lookup for every packet, significantly reducing processing time. Label switching also enables traffic engineering, allowing network operators to define explicit paths, control bandwidth usage, and ensure QoS for critical applications such as VoIP or video.
ARP (Address Resolution Protocol): ARP is used in Ethernet networks to map IP addresses to MAC addresses. While essential for local network communication, ARP does not influence MPLS label assignment or forwarding and operates primarily at Layer 2.
NAT (Network Address Translation): NAT modifies IP addresses in packet headers to allow communication between private and public networks or to conserve IP addresses. NAT is unrelated to MPLS label switching, as it operates at the IP layer rather than the MPLS label layer.
DHCP (Dynamic Host Configuration Protocol): DHCP automatically assigns IP addresses and configuration parameters to hosts on a network. Like ARP and NAT, DHCP operates independently of MPLS and does not participate in label-based forwarding or path selection.
Question 56:
Which STP variant allows multiple spanning-tree instances for different VLANs?
MSTP
B. RSTP
C. PVST+
D. STP
Answer: A. MSTP
Explanation:
Multiple Spanning Tree Protocol (MSTP) allows multiple VLANs to share a single spanning-tree instance, reducing the number of STP calculations and improving efficiency. RSTP provides rapid convergence, PVST+ runs a separate instance per VLAN, and classic STP provides one spanning tree for the entire network. MSTP is widely used in large enterprise networks to optimize resources. Spanning Tree Protocol (STP) is essential in Ethernet networks to prevent Layer 2 loops, which can cause broadcast storms and network instability. Over time, multiple versions of STP have been developed to address performance, scalability, and convergence requirements. The four key variants are STP, RSTP, PVST+, and MSTP, each serving different needs.
STP (Spanning Tree Protocol): The original IEEE 802.1D standard, STP creates a single spanning-tree instance for the entire network. It prevents loops by selectively blocking redundant links, allowing only one active path between switches. While effective, STP has slow convergence, often taking 30–50 seconds to reconfigure after a topology change, which can impact network availability.
RSTP (Rapid Spanning Tree Protocol): Defined in IEEE 802.1w, RSTP improves convergence times significantly compared to classic STP. By introducing new port roles and states, RSTP can respond to topology changes within a few seconds. It maintains backward compatibility with STP, enabling gradual upgrades in existing networks without complete redesign.
PVST+ (Per-VLAN Spanning Tree Plus): PVST+ is a Cisco enhancement that runs a separate spanning-tree instance for each VLAN. This allows load balancing across multiple links by designating different root bridges for different VLANs. However, in large networks with many VLANs, PVST+ increases CPU load and memory usage due to multiple STP instances.
MSTP (Multiple Spanning Tree Protocol): MSTP, defined in IEEE 802.1s, allows multiple VLANs to share a single spanning-tree instance, grouping VLANs into regions. This reduces the number of STP calculations, conserves switch resources, and improves efficiency while maintaining loop prevention. MSTP also supports rapid convergence like RSTP and is widely used in large enterprise networks where scalability and resource optimization are critical.
Question 57:
Which Cisco technology provides redundancy for access switches in a campus network?
HSRP
B. VSS
C. EtherChannel
D. VLAN
Answer: B. VSS
Explanation:
Virtual Switching System (VSS) allows two Cisco Catalyst switches to operate as a single logical switch, providing redundancy and simplified management. HSRP provides gateway redundancy, EtherChannel aggregates links, and VLANs segment traffic, but does not provide switch redundancy. VSS improves bandwidth utilization and eliminates STP loops between redundant access switches. Virtual Switching System (VSS) is a Cisco technology that allows two physical Catalyst switches to operate as a single logical switch. This provides both redundancy and simplified network management by enabling a single control plane and a unified management interface. VSS helps improve bandwidth utilization and eliminates Spanning Tree Protocol (STP) loops between redundant access switches by allowing all links to be active simultaneously, unlike traditional redundant topologies, where some links are blocked to prevent loops.
HSRP (Hot Standby Router Protocol) is a redundancy protocol that provides gateway failover for hosts. While HSRP ensures continuous default gateway availability, it operates at Layer 3 and does not merge multiple switches into a single logical entity like VSS.
EtherChannel is a method of aggregating multiple physical links into a single logical link to increase bandwidth and provide redundancy at Layer 2. Although EtherChannel improves link utilization and resiliency, it does not combine two switches into one logical switch or simplify management of redundant devices.
VLANs (Virtual LANs) segment traffic within a network to create isolated broadcast domains. While VLANs help organize and secure traffic, they do not provide redundancy or link aggregation.
In summary, VSS is a powerful solution for switch-level redundancy and efficiency, combining two physical switches into one logical system, whereas HSRP, EtherChannel, and VLANs address gateway redundancy, link aggregation, and traffic segmentation, respectively. VSS complements these technologies to create resilient, high-performance enterprise networks.
Question 58:
Which command verifies the MPLS LSP operational state?
A.Showw MPLS LDP neighbors
B. show ip route
C. show interfaces
D. show ip protocols
Answer: A. show mpls ldp neighbors
Explanation:
The show mpls ldp neighbors command displays LDP neighbor relationships, session status, and label exchanges. This ensures that MPLS LSPs are established correctly. Show ip route shows IP routes, show interfaces shows link status, and show ip protocols shows routing protocols, but they do not display label-specific information. Proper verification of LDP neighbors is critical for MPLS troubleshooting. In MPLS networks, verifying LDP (Label Distribution Protocol) neighbor relationships is crucial to ensure Label Switched Paths (LSPs) function correctly. The show mpls ldp neighbors command displays LDP peers, session status, and label exchange details, making it the primary tool for MPLS troubleshooting. In contrast, show ip route lists IP routes, show interfaces provides interface status and statistics, and show ip protocols displays routing protocol parameters. While these commands are useful for general network monitoring, only showing MPLS LDP neighbors provides detailed information about label distribution and neighbor adjacencies, essential for maintaining MPLS connectivity.
Question 59:
Which type of NAT allows multiple internal hosts to share a single public IP using different ports?
PAT (NAT Overload)
B. Dynamic NAT
C. Static NAT
D. NAT64
Answer: A. PAT (NAT Overload)
Explanation:
Port Address Translation (PAT) allows many internal hosts to share one public IP by mapping each connection to a unique source port. Dynamic NAT maps internal IPs to a pool of public IPs with one-to-one translation. Static NAT provides permanent one-to-one mapping, and NAT64 facilitates IPv6-to-IPv4 communication. PAT maximizes IP address usage efficiently, especially in IPv4-constrained networks. Port Address Translation (PAT), also known as NAT Overload, is a widely used method to allow multiple internal hosts to share a single public IP address. PAT achieves this by mapping each internal connection to a unique source port number, enabling thousands of devices to access external networks using a single IP. This approach maximizes the efficient use of scarce IPv4 addresses and is ideal for networks with limited public IP resources.
Dynamic NAT maps internal private IP addresses to a pool of public IP addresses on a one-to-one basis. Unlike PAT, each internal host requires a unique public IP from the pool. While dynamic NAT allows internal hosts to communicate externally without exposing their private IPs, it is limited by the size of the available public IP pool.
Static NAT provides a permanent, fixed one-to-one mapping between an internal private IP and a public IP. It is commonly used for servers that need to be consistently reachable from the Internet, such as web or mail servers.
NAT64 is a specialized form of NAT that enables communication between IPv6 clients and IPv4 servers. It translates IPv6 addresses to IPv4 addresses and vice versa, facilitating IPv6 adoption while maintaining compatibility with legacy IPv4 infrastructure.
Question 60:
Which Cisco wireless feature allows the AP to remain operational during temporary controller unavailability while forwarding traffic locally?
FlexConnect
B. CAPWAP
C. LWAPP
D. Rogue Detection
Answer: A. FlexConnect
Explanation:
FlexConnect allows lightweight APs to forward traffic locally, even when connectivity to the controller is lost, maintaining network service. CAPWAP and LWAPP tunnel traffic to the controller, which could create disruption during controller outages. Rogue Detection identifies unauthorized APs but does not enable local switching. FlexConnect is commonly used in branch office deployments for high availability.FlexConnect is a Cisco deployment mode for lightweight access points (APs) that enables local switching of client traffic. This means that APs can forward traffic directly to the local network instead of tunneling it back to a central wireless controller. FlexConnect is particularly useful in branch office deployments or remote sites, where WAN connectivity to the controller may be limited or unreliable. Even if the controller becomes unavailable, FlexConnect-enabled APs can continue to provide network access, ensuring high availability and continuity of service.
CAPWAP (Control and Provisioning of Wireless Access Points) is the standard protocol used to manage lightweight APs by tunneling control and client traffic to a wireless controller. While CAPWAP centralizes management and policy enforcement, it relies on continuous connectivity to the controller. If the controller is unreachable, traffic may be disrupted.
LWAPP (Lightweight Access Point Protocol) is an older protocol similar to CAPWAP, used to tunnel traffic to controllers. It has been largely replaced by CAPWAP in modern networks due to improved standardization and features.
Rogue Detection is a security feature that allows APs or controllers to detect unauthorized or rogue APs in the environment. While critical for securing wireless networks, rogue detection does not provide traffic switching or failover capabilities like FlexConnect.
