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Q1. Which routing protocol is commonly used to provide scalable interior gateway routing within an enterprise network?

1. BGP
   2. OSPF
   3. SMTP
   4. FTP

Correct Answer: 2. OSPF

Explanation: OSPF is a link-state interior gateway protocol designed for routing within an autonomous system. It uses areas to improve scalability and reduce the size of the routing database that each router must maintain. OSPF calculates the shortest path using the SPF algorithm and can quickly adapt to topology changes. BGP is primarily used between autonomous systems, while SMTP and FTP are application-layer protocols unrelated to IP routing. In the ENARSI exam, understanding OSPF areas, neighbor relationships, LSAs, route selection, and troubleshooting is particularly important. OSPF is widely deployed in enterprise environments because it provides fast convergence and supports hierarchical network designs.

Q2. Which OSPF LSA type is used by a router to describe its directly connected links within an area?

1. Type 1
   2. Type 2
   3. Type 3
   4. Type 5

Correct Answer: 1. Type 1

Explanation: A Type 1 LSA, known as a Router LSA, is generated by every OSPF router and describes the router’s links, interfaces, costs, and neighboring relationships within an OSPF area. These LSAs are flooded throughout the originating area. Type 2 LSAs are generated by the DR on multiaccess networks, Type 3 LSAs are generated by ABRs to advertise inter-area routes, and Type 5 LSAs are used for external routes. Understanding LSA types is essential when troubleshooting OSPF because the presence, absence, or incorrect propagation of an LSA can explain why a route does or does not appear in the routing table.

Q3. Which command displays the OSPF neighbor relationships on a Cisco router?

1. show ip route ospf
   2. show ip ospf neighbor
   3. show ospf database
   4. show ip protocols ospf

Correct Answer: 2. show ip ospf neighbor

Explanation: The show ip ospf neighbor command displays OSPF neighbor information, including the neighbor router ID, priority, state, dead timer, and interface. It is one of the most important commands for troubleshooting OSPF adjacency problems. If a neighbor is not reaching the FULL state when expected, an administrator should investigate parameters such as area ID, hello and dead intervals, authentication, network type, router IDs, and connectivity. The show ip route ospf command focuses on routes learned through OSPF rather than neighbor status. In ENARSI troubleshooting scenarios, checking neighbor relationships is often an important first step.

Q4. Which OSPF network type normally elects a designated router and backup designated router?

1. Point-to-point
   2. Loopback
   3. Broadcast
   4. Point-to-multipoint

Correct Answer: 3. Broadcast

Explanation: OSPF broadcast network types, commonly associated with Ethernet networks, elect a Designated Router (DR) and Backup Designated Router (BDR). The purpose is to reduce the number of full OSPF adjacencies required on a multiaccess segment. Instead of every router forming a full adjacency with every other router, routers establish full relationships primarily with the DR and BDR. DR election uses OSPF interface priority first and router ID as a tiebreaker. Point-to-point networks do not require DR or BDR elections. Understanding DR and BDR behavior is important for diagnosing OSPF adjacency and flooding issues on Ethernet networks.

Q5. Which command can be used to verify the OSPF process ID and configured areas on a Cisco router?

1. show ip protocols
   2. show interfaces
   3. show arp
   4. show cdp neighbors

Correct Answer: 1. show ip protocols

Explanation: The show ip protocols command provides useful information about active routing protocols on a Cisco router. For OSPF, it can display the process ID, router ID, networks participating in the routing process, areas, passive interfaces, administrative distance, and other protocol parameters. This makes the command valuable when troubleshooting routing configuration. show interfaces provides interface-level information, show arp displays address-resolution entries, and show cdp neighbors provides information about directly connected Cisco devices. When an OSPF route is unexpectedly missing, show ip protocols can help determine whether the relevant interface or network has actually been included in the OSPF process.

Q6. What is the primary purpose of an OSPF area?

1. To eliminate routing tables
   2. To reduce the size of the OSPF link-state database and improve scalability
   3. To replace IP addressing
   4. To provide encryption for OSPF packets

Correct Answer: 2. To reduce the size of the OSPF link-state database and improve scalability

Explanation: OSPF areas provide hierarchical organization that improves routing scalability. A router maintains detailed link-state information for its own area, while summarized information can be exchanged between areas through Area Border Routers (ABRs). This limits the size of the link-state database and reduces SPF calculations when changes occur elsewhere in the network. Area 0 is the backbone area and provides connectivity between non-backbone areas in a conventional OSPF design. OSPF areas do not provide encryption or replace IP addressing. Proper area design is important for large enterprise networks and is a significant ENARSI troubleshooting and configuration topic.

Q7. Which protocol is commonly used to exchange routing information between autonomous systems?

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

Correct Answer: 3. BGP

Explanation: Border Gateway Protocol (BGP) is the primary exterior gateway protocol used to exchange routing information between autonomous systems. BGP is designed for scalability and policy-based routing rather than simply selecting the shortest path. It uses attributes such as local preference, AS path, MED, origin, and weight to influence route selection. OSPF, EIGRP, and RIP are primarily interior gateway protocols used within autonomous systems. Cisco ENARSI heavily emphasizes BGP configuration and troubleshooting, including neighbor relationships, route advertisement, route filtering, path selection, and attributes. Understanding the difference between internal and external routing protocols is fundamental when analyzing enterprise routing problems.

Q8. Which BGP attribute is commonly used to prefer one outbound path from an autonomous system?

1. Local preference
   2. MED
   3. Origin
   4. AS-path length

Correct Answer: 1. Local preference

Explanation: Local preference is a BGP attribute used within an autonomous system to influence the preferred exit point for outbound traffic. A higher local-preference value is preferred. Because local preference is propagated throughout an autonomous system through iBGP, it is useful when an organization wants multiple routers to select the same exit path. MED is generally used to influence how external autonomous systems enter the local network, while AS-path length is another BGP path-selection factor. Understanding BGP attributes and their direction of influence is essential for ENARSI troubleshooting because incorrect attribute values can cause traffic to use an unexpected path.

Q9. What is the main function of route redistribution?

1. Encrypt routing updates
   2. Exchange routes between different routing protocols or routing processes
   3. Disable routing protocols
   4. Replace all static routes

Correct Answer: 2. Exchange routes between different routing protocols or routing processes

Explanation: Route redistribution allows routes learned by one routing protocol or routing source to be introduced into another routing protocol. For example, an enterprise may need to redistribute EIGRP routes into OSPF or connect a static-routing domain to an OSPF domain. Redistribution must be carefully designed because different protocols use different metrics, administrative distances, and route-selection mechanisms. Poor redistribution can cause routing loops, suboptimal paths, or excessive routing information. ENARSI places significant emphasis on redistribution, including route maps, filtering, tagging, metric conversion, and troubleshooting. Route redistribution should normally be controlled rather than allowing every available route to enter another protocol.

Q10. Which mechanism helps prevent routing loops when routes are redistributed between routing protocols?

1. Route tagging
   2. DHCP
   3. NAT overload
   4. ARP inspection

Correct Answer: 1. Route tagging

Explanation: Route tagging can help identify routes that have already passed through a redistribution boundary. Administrators can use route maps and tags to mark routes when they are redistributed and then prevent those tagged routes from being redistributed back into the original routing domain. This helps avoid routing loops in complex environments where multiple routing protocols exchange information. Route tagging does not itself alter the route’s destination; instead, it provides an administrative label that can be matched by routing policy. ENARSI troubleshooting commonly involves identifying redistribution loops and designing filtering policies that prevent routes from repeatedly moving between routing protocols.

Q11. Which EIGRP metric component is primarily used by default to calculate the composite metric?

1. Bandwidth and delay
   2. CPU utilization and memory
   3. MTU and hop count
   4. Packet size and latency only

Correct Answer: 1. Bandwidth and delay

Explanation: EIGRP’s classic composite metric uses bandwidth and delay by default. Other possible components include reliability and load, although the default K values give those factors no influence. EIGRP calculates the metric based on the configured K values and interface characteristics. Bandwidth represents the minimum bandwidth along the path, while delay represents the accumulated delay. MTU is carried in EIGRP information but is not part of the classic composite metric calculation. Understanding EIGRP metric behavior is important for troubleshooting situations where a router selects an unexpected path. Administrators should also understand feasible successors, the feasibility condition, and EIGRP topology-table information.

Q12. Which EIGRP route state indicates that a route is actively being queried because no feasible successor is currently available?

1. Passive
   2. Active
   3. Established
   4. Standby

Correct Answer: 2. Active

Explanation: An EIGRP route enters the Active state when the router does not have a feasible successor and must query neighbors to find an alternative path. A route remaining Active for an excessive period can indicate an EIGRP stuck-in-active problem. Possible causes include slow responses, network instability, insufficient query boundaries, or connectivity problems. A Passive route is stable and has a valid successor. Troubleshooting EIGRP therefore includes examining the topology table, neighbor relationships, query behavior, and convergence characteristics. EIGRP summarization and stub routers can also help limit query propagation and improve stability in larger networks.

Q13. Which command provides detailed information about routes stored in the EIGRP topology table?

1. show ip eigrp topology
   2. show ip route static
   3. show arp
   4. show interfaces status

Correct Answer: 1. show ip eigrp topology

Explanation: The show ip eigrp topology command displays information from the EIGRP topology table. It can show successor routes, feasible successors, reported distances, feasible distances, and route states. This information is especially useful when troubleshooting why EIGRP selected a particular path or why a feasible successor is not available. The routing table shows only the routes selected for forwarding, whereas the topology table contains additional candidate paths learned from EIGRP neighbors. ENARSI candidates should understand the relationship between the neighbor table, topology table, and routing table because these three views provide different information during EIGRP troubleshooting.

Q14. Which technology allows multiple private IPv4 addresses to share a single public IPv4 address by using different port numbers?

1. Static routing
   2. PAT
   3. GRE
   4. VRF

Correct Answer: 2. PAT

Explanation: Port Address Translation (PAT), often called NAT overload, allows many internal private IPv4 addresses to share a single public IPv4 address. PAT distinguishes individual connections by using unique TCP or UDP source-port values. This conserves public IPv4 address space and is widely used at enterprise Internet edges. Static NAT creates a fixed one-to-one mapping, while GRE provides tunneling and VRF provides separate routing tables. When troubleshooting NAT, administrators should examine translations, configuration statements, interfaces designated as inside or outside, and access rules. Cisco ENARSI questions frequently test NAT operation and troubleshooting commands.

Q15. Which command displays active NAT translations on a Cisco router?

1. show ip nat translations
   2. show ip route nat
   3. show nat interfaces
   4. show ip protocols nat

Correct Answer: 1. show ip nat translations

Explanation: The show ip nat translations command displays the active NAT translation table. It can show inside-local, inside-global, outside-local, and outside-global addresses, along with protocol and port information when applicable. This command is useful when determining whether traffic is being translated as expected. Administrators can also use show ip nat statistics to examine counters and configured interfaces. If no translation appears, troubleshooting should include verifying NAT configuration, traffic flow, interface roles, and access-control policies. Understanding NAT translation tables is important for ENARSI because NAT problems can appear to be routing or connectivity problems when the underlying issue is address translation.

Q16. Which technology provides logically separate routing tables on the same physical router?

1. VLAN trunking
   2. VRF
   3. EtherChannel
   4. CDP

Correct Answer: 2. VRF

Explanation: Virtual Routing and Forwarding (VRF) allows a router to maintain multiple independent routing tables on the same physical device. Each VRF can contain separate routes and interfaces, allowing overlapping IP address spaces to coexist. VRFs are commonly used in service-provider and enterprise environments to isolate customers, departments, or network services. A route in one VRF is not automatically available to another VRF. Troubleshooting therefore requires commands that specify the appropriate VRF when checking routes, interfaces, or connectivity. Understanding VRF concepts is essential for ENARSI because many enterprise and service-provider designs depend on routing-table separation.

Q17. Which tunneling protocol is commonly used to encapsulate IPv4 packets inside an IP tunnel?

1. GRE
   2. DHCP
   3. ARP
   4. STP

Correct Answer: 1. GRE

Explanation: Generic Routing Encapsulation (GRE) creates a tunnel by encapsulating one network-layer protocol inside another IP packet. GRE is commonly used to create logical point-to-point tunnels between routers across an intermediate network. It can carry routing protocol traffic because it provides a virtual point-to-point interface. However, GRE itself does not provide encryption. When security is required, GRE is often combined with IPsec. ENARSI troubleshooting may involve checking tunnel source and destination, tunnel line protocol status, routing to the tunnel destination, MTU, and keepalive behavior. Understanding GRE is especially important when implementing overlay connectivity across routed infrastructure.

Q18. What is the primary purpose of IPsec?

1. Provide secure IP communication through authentication and encryption
   2. Assign IP addresses automatically
   3. Calculate OSPF metrics
   4. Replace Ethernet switching

Correct Answer: 1. Provide secure IP communication through authentication and encryption

Explanation: IPsec provides security for IP communications by offering mechanisms for confidentiality, integrity, authentication, and anti-replay protection. It is commonly used to secure site-to-site VPN connections across untrusted networks. IPsec commonly works with Internet Key Exchange (IKE) to establish security associations and negotiate cryptographic parameters. GRE can provide routing-protocol support across a tunnel but does not encrypt traffic by itself, so GRE over IPsec is a common design. For ENARSI, administrators should understand IKE phases, transform sets or proposals, security associations, tunnel interfaces, and troubleshooting commands used to verify VPN operation.

Q19. Which protocol is commonly used to dynamically establish and maintain IPsec security associations?

1. IKE
   2. FTP
   3. SNMP
   4. TFTP

Correct Answer: 1. IKE

Explanation: Internet Key Exchange (IKE) is used to negotiate security parameters and establish security associations for IPsec. IKE helps authenticate peers and negotiate cryptographic algorithms, keys, and other security parameters. IKEv1 uses two phases, while IKEv2 provides a more streamlined exchange process. When troubleshooting an IPsec VPN, administrators should verify peer reachability, authentication credentials, encryption and hashing parameters, Diffie-Hellman settings, proposals, policies, and security associations. If IKE negotiation fails, IPsec may never establish the required secure tunnel. Understanding IKE is therefore an important part of Cisco ENARSI VPN troubleshooting.

Q20. Which command is commonly used to verify IPsec security associations on a Cisco IOS router?

1. show crypto ipsec sa
   2. show ip ospf database
   3. show crypto routing
   4. show ip bgp neighbor

Correct Answer: 1. show crypto ipsec sa

Explanation: The show crypto ipsec sa command provides information about active IPsec security associations and packet counters. It can help determine whether encrypted and decrypted traffic is actually passing through an IPsec tunnel. Useful counters include encapsulated packets, encrypted packets, decapsulated packets, and decrypted packets. If the counters remain unchanged, the administrator should investigate traffic matching, routing, access-control policies, tunnel configuration, and peer negotiation. Other commands are useful for OSPF or BGP but do not directly verify IPsec data-plane operation. This command is therefore an important troubleshooting tool for Cisco VPN scenarios covered by ENARSI.