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Q101. Which command displays the current IPv4 routing table on a Cisco router?

1) show interfaces
2) show ip route
3) show ip protocols
4) show route table

Correct Answer: 2) show ip route

Explanation: The show ip route command displays the IPv4 routing table maintained by a Cisco router. It shows connected, static, and dynamically learned routes, along with routing codes, destination networks, administrative distance, metric, next-hop information, and outgoing interfaces. This command is one of the most important troubleshooting tools because it allows administrators to determine how the router will forward packets toward a destination. If a route is missing, the administrator can investigate the routing protocol, interface status, static configuration, or redistribution settings. Reviewing the routing table is an essential step when diagnosing connectivity problems.

Q102. Which IPv6 address type is designed for communication with the nearest available member of a group?

1) Unicast
2) Broadcast
3) Anycast
4) Multicast

Correct Answer: 3) Anycast

Explanation: An IPv6 anycast address identifies multiple interfaces, usually on different devices, with the same address. A packet sent to an anycast address is delivered to the nearest or best destination according to the routing topology. Anycast is useful for services that should be available from multiple locations, such as DNS or distributed network services. IPv6 does not use broadcast addresses in the same way IPv4 does. Instead, multicast and other mechanisms are used for functions traditionally associated with broadcast. Understanding IPv6 address types is important when designing and troubleshooting modern IP networks.

Q103. Which protocol is used by IPv6 hosts to discover neighboring devices and routers?

1) NDP
2) FTP
3) SNMP
4) TFTP

Correct Answer: 1) NDP

Explanation: Neighbor Discovery Protocol, or NDP, is an essential IPv6 protocol that uses ICMPv6 messages to provide functions such as neighbor discovery, router discovery, address resolution, and duplicate address detection. NDP replaces several functions that IPv4 commonly performs using ARP and related mechanisms. Router Solicitation and Router Advertisement messages help hosts discover IPv6 routers and obtain network configuration information. Neighbor Solicitation and Neighbor Advertisement messages are used for neighbor communication and address resolution. Understanding NDP is important when troubleshooting IPv6 connectivity, especially problems involving default gateways, address resolution, or duplicate addresses.

Q104. What is the primary purpose of a loopback interface on a Cisco router?

1) Provide a physical Ethernet connection
2) Provide a stable logical interface
3) Disable routing updates
4) Increase WAN bandwidth

Correct Answer: 2) Provide a stable logical interface

Explanation: A loopback interface is a logical interface that is not directly associated with a physical port. Because it remains operational as long as the router has an active system state, it provides a stable address for several networking functions. Loopbacks are commonly used for router identification, management, routing protocol identifiers, and network services. For example, OSPF and BGP can use a loopback address as the router ID. Loopbacks are also useful for testing reachability because their status is generally independent of an individual physical interface. This makes them valuable in both network design and troubleshooting.

Q105. Which command verifies whether an interface is operational and displays its IP address and status?

1) show ip interface brief
2) show running-config route
3) show ip protocols
4) show interfaces route

Correct Answer: 1) show ip interface brief

Explanation: The show ip interface brief command provides a concise summary of router interfaces, including their IP addresses, status, and protocol state. It is one of the quickest commands for identifying interface problems. The Status column indicates whether the physical interface is operational, while the Protocol column indicates whether the Layer 2 protocol is functioning. If an interface shows administratively down, it has been disabled with the shutdown command. If the status and protocol values do not indicate normal operation, administrators can investigate cabling, encapsulation, configuration, or remote-side problems.

Q106. Which routing protocol uses Dijkstra’s Shortest Path First algorithm?

1) EIGRP
2) RIP
3) OSPF
4) BGP

Correct Answer: 3) OSPF

Explanation: OSPF uses the Shortest Path First algorithm, commonly known as the Dijkstra algorithm, to calculate the shortest path through an area. OSPF routers maintain a link-state database containing information about the network topology. When topology changes occur, routers use this information to recalculate the best paths. The resulting shortest-path tree is then used to determine routes for the routing table. OSPF’s link-state approach allows relatively fast convergence and supports hierarchical designs using areas. Understanding SPF calculations is useful when analyzing OSPF route selection and troubleshooting unexpected routing behavior.

Q107. Which EIGRP packet type is used to discover and maintain neighbor relationships?

1) Query
2) Hello
3) Reply
4) Update

Correct Answer: 2) Hello

Explanation: EIGRP Hello packets are used to discover neighboring EIGRP routers and maintain neighbor relationships. EIGRP routers periodically send Hello messages through participating interfaces. When compatible routers receive these packets, they can establish neighbor adjacencies and begin exchanging routing information. If Hello packets are no longer received within the appropriate hold time, the neighbor relationship can be declared down. EIGRP also uses Update, Query, Reply, and Acknowledgment packets for other routing functions. When troubleshooting an EIGRP adjacency, administrators should verify interface configuration, autonomous system values, authentication, network reachability, and relevant timers.

Q108. Which BGP attribute helps prevent routing loops between autonomous systems?

1) Local Preference
2) Weight
3) AS_PATH
4) MED

Correct Answer: 3) AS_PATH

Explanation: The BGP AS_PATH attribute records the sequence of autonomous systems that a route advertisement has traversed. When a BGP router receives an advertisement containing its own autonomous system number in the AS_PATH, it normally rejects the route because accepting it could create a routing loop. AS_PATH also influences path selection, with shorter paths generally preferred when other relevant attributes are equal. Administrators can modify AS_PATH behavior using policy mechanisms when necessary. Because it serves both loop prevention and path-selection purposes, AS_PATH is one of the most important attributes in external BGP operations.

Q109. Which command can be used to verify BGP routes received from a specific neighbor?

1) show ip bgp neighbors
2) show ip bgp neighbor <address> received-routes
3) show bgp interfaces
4) show ip protocols bgp

Correct Answer: 2) show ip bgp neighbor <address> received-routes

Explanation: The show ip bgp neighbor <address> received-routes command can be used to examine routes received from a specific BGP neighbor, when the appropriate inbound soft-reconfiguration capability is configured. It helps administrators understand what prefixes are being received before or alongside inbound policy processing. This is useful when troubleshooting prefix filtering, route maps, or unexpected route advertisements. The neighbor address must be replaced with the actual BGP peer address. Other commands provide different information, such as session summaries or the local BGP table, but this command focuses specifically on routes received from a particular peer.

Q110. What is the main purpose of BGP communities?

1) Encrypt BGP updates
2) Tag routes so policies can be applied
3) Replace AS_PATH
4) Establish TCP sessions

Correct Answer: 2) Tag routes so policies can be applied

Explanation: BGP communities are attributes that allow routes to be tagged with values representing a particular policy or characteristic. Network administrators can then use route maps and other policies to match those communities and take actions such as changing Local Preference, controlling route advertisements, or applying filtering. Communities make BGP policy management more scalable because administrators can apply consistent policies to groups of routes instead of creating individual rules for every prefix. Well-known communities such as no-export also provide standardized policy behavior. Communities are therefore an important tool for managing complex BGP routing policies.

Q111. Which OSPF LSA type is generated by an ASBR to advertise external routes?

1) Type 1
2) Type 2
3) Type 3
4) Type 5

Correct Answer: 4) Type 5

Explanation: OSPF Type 5 LSAs are used to advertise external routes throughout an OSPF autonomous system, except in areas where external LSAs are restricted by area type. An Autonomous System Boundary Router, or ASBR, generates Type 5 LSAs when it redistributes routes from another routing source into OSPF. These routes can originate from another routing protocol, static routes, or connected networks. Type 5 LSAs are different from Type 3 summary LSAs, which are generated by ABRs to advertise inter-area routes. Understanding LSA types is essential when troubleshooting redistribution and missing external OSPF routes.

Q112. What is the function of an OSPF Area Border Router (ABR)?

1) Connect different OSPF areas
2) Replace the DR
3) Provide DHCP services
4) Encrypt OSPF packets

Correct Answer: 1) Connect different OSPF areas

Explanation: An OSPF Area Border Router, or ABR, connects one OSPF area to another, typically connecting a non-backbone area to Area 0. An ABR maintains a separate link-state database for each connected area and can generate summary LSAs to advertise routes between areas. This hierarchical structure reduces the size of individual link-state databases and limits the scope of SPF calculations. Proper ABR operation is therefore important in large OSPF networks. When troubleshooting inter-area routing, administrators should verify Area 0 connectivity, interface area assignments, LSAs, and the routing information exchanged between the areas.

Q113. Which OSPF area type allows external routes to be represented using Type 7 LSAs?

1) Stub area
2) NSSA
3) Totally stubby area
4) Backbone area

Correct Answer: 2) NSSA

Explanation: A Not-So-Stubby Area, or NSSA, allows external routes to be introduced into an otherwise restricted OSPF area. External routes inside an NSSA are represented using Type 7 LSAs. An NSSA is useful when an organization needs redistribution within an area but still wants to limit the amount of external routing information entering the area. An NSSA can use an appropriate ABR to translate Type 7 LSAs into Type 5 LSAs when the routes need to be advertised into other OSPF areas. Understanding NSSA behavior is important when troubleshooting redistribution and external route visibility.

Q114. Which MPLS label is typically associated with the VPN service in an MPLS Layer 3 VPN?

1) VPN label
2) Ethernet label
3) ARP label
4) DHCP label

Correct Answer: 1) VPN label

Explanation: In an MPLS Layer 3 VPN, a VPN label is used to identify the appropriate customer VRF or VPN forwarding context at the destination PE router. MPLS VPN forwarding commonly uses a transport label and a VPN service label. The transport label helps carry traffic across the provider core, while the VPN label allows the receiving PE to determine the correct VPN context. This separation enables multiple customers to share the same provider infrastructure while maintaining logical routing isolation. Troubleshooting MPLS VPN forwarding may therefore require verification of labels, LDP or other label protocols, MP-BGP information, and VRF configuration.

Q115. Which command displays VRFs configured on a Cisco router?

1) show ip vrf
2) show vrf routing only
3) show ip vpn table
4) show mpls vrf

Correct Answer: 1) show ip vrf

Explanation: The show ip vrf command displays the VRFs configured on a Cisco router and provides information about their names and associated interfaces. This command is useful when verifying whether an interface has been assigned to the expected VRF. VRF configuration is especially important in environments where multiple independent routing tables are maintained. If an interface is accidentally placed in the wrong VRF, it may lose access to routes that exist in the global routing table or another VRF. Administrators can use additional VRF-specific routing commands to investigate route availability after confirming the VRF assignment.

Q116. Which DMVPN component maintains mappings between tunnel addresses and NBMA addresses?

1) NHRP
2) STP
3) DHCP
4) BFD

Correct Answer: 1) NHRP

Explanation: NHRP maintains mappings between logical tunnel addresses and underlying NBMA addresses in DMVPN environments. These mappings allow DMVPN routers to determine how to reach remote peers across the underlying transport network. The hub can maintain registrations from spokes, while spokes can dynamically learn the required information for other peers. NHRP is therefore essential to the dynamic nature of DMVPN. Administrators can use show ip nhrp to inspect mappings and registration information. If NHRP entries are missing or incorrect, dynamic tunnel establishment and spoke-to-spoke communication may fail even when basic IP connectivity exists.

Q117. What is the primary benefit of BFD in a routed network?

1) Provides rapid detection of forwarding-path failures
2) Encrypts routing updates
3) Assigns IP addresses automatically
4) Replaces all routing protocols

Correct Answer: 1) Provides rapid detection of forwarding-path failures

Explanation: Bidirectional Forwarding Detection, or BFD, provides rapid detection of failures between neighboring network devices. Routing protocols may use relatively long timers to detect a failed neighbor, while BFD can detect forwarding problems much more quickly. Routing protocols such as OSPF and BGP can use BFD information to trigger faster convergence when a path fails. BFD does not replace the routing protocol itself; instead, it provides a fast failure-detection mechanism that routing protocols can use. This makes BFD particularly useful in networks where rapid convergence is important and traditional protocol timers are too slow.

Q118. Which mechanism can limit the maximum number of prefixes accepted from a BGP neighbor?

1) prefix-limit
2) ip helper-address
3) passive-interface
4) default-information originate

Correct Answer: 1) prefix-limit

Explanation: A BGP prefix limit can be configured to control how many prefixes a router accepts from a particular BGP neighbor. This provides an important protection mechanism because an unexpected routing-table increase can consume significant memory and processing resources. When the configured threshold is reached, the router can take a predefined action depending on the configuration, such as generating a warning or shutting down the session. Prefix limits are particularly useful when establishing relationships with external networks where the expected number of received routes is known. Properly configured limits help protect router resources from accidental or abnormal route advertisements.

Q119. Which command can display the interfaces participating in an EIGRP process?

1) show ip eigrp interfaces
2) show ip bgp interfaces
3) show eigrp neighbors only
4) show interfaces eigrp database

Correct Answer: 1) show ip eigrp interfaces

Explanation: The show ip eigrp interfaces command provides information about interfaces participating in EIGRP. It can display details such as the interface name, EIGRP process, peers, authentication status, pacing information, and other interface-related parameters. This makes it useful when troubleshooting why a particular interface is not forming EIGRP adjacencies or exchanging routes. Administrators can compare the output with the EIGRP network configuration and interface settings. If an expected interface is absent, the routing process configuration or interface participation should be examined before investigating more advanced routing issues.

Q120. What is the main purpose of route summarization?

1) Increase the number of routing table entries
2) Reduce routing information and improve scalability
3) Disable routing protocols
4) Encrypt route advertisements

Correct Answer: 2) Reduce routing information and improve scalability

Explanation: Route summarization combines multiple more-specific network prefixes into a single summarized route. This reduces the amount of routing information that routers need to maintain and advertise. Summarization can improve scalability, reduce routing-table size, and limit the impact of topology changes. For example, several contiguous networks can potentially be represented by one larger prefix when their addressing structure permits it. However, incorrect summarization can create black holes if the summary is advertised for destinations that are not actually reachable. Administrators should therefore carefully plan address allocation and verify routing behavior after implementing route summarization.