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Q201. Which OSPF network type is commonly used on a point-to-point serial link and does not require DR/BDR election?

1) Broadcast
2) Nonbroadcast
3) Point-to-point
4) Point-to-multipoint nonbroadcast

Correct Answer: 3) Point-to-point

Explanation:
The OSPF point-to-point network type is designed for links connecting exactly two routers. Because there is no multiaccess segment containing multiple OSPF routers, a Designated Router (DR) and Backup Designated Router (BDR) are not required. This simplifies adjacency formation and reduces unnecessary OSPF election activity. Point-to-point interfaces typically form an adjacency directly with the neighboring router and exchange link-state information normally. Understanding OSPF network types is important when troubleshooting adjacency problems, especially on serial or other dedicated links. Broadcast networks such as Ethernet use DR and BDR elections, while point-to-point networks do not require them.

Q202. Which OSPF LSA type is used by an Area Border Router to advertise networks from one area into another area?

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

Correct Answer: 3) Type 3

Explanation:
OSPF Type 3 LSAs, known as Summary LSAs, are generated by Area Border Routers (ABRs) to advertise inter-area routes. An ABR connects multiple OSPF areas and uses Type 3 LSAs to communicate networks learned from one area into another area. This allows routers in different OSPF areas to learn about remote networks without requiring every router to maintain the complete topology database of every area. Type 1 LSAs describe router information within an area, while Type 2 LSAs describe transit network information. Type 5 LSAs are used for external routes redistributed into OSPF. Therefore, Type 3 is the appropriate answer.

Q203. What is the main purpose of configuring an EIGRP authentication key?

1) Increase routing bandwidth
2) Verify that EIGRP neighbors are authorized
3) Change the EIGRP metric
4) Create a default route

Correct Answer: 2) Verify that EIGRP neighbors are authorized

Explanation:
EIGRP authentication provides a method for verifying that routing updates are coming from a trusted neighbor. When authentication is configured, routers use a shared key to validate EIGRP packets. This helps prevent unauthorized devices from forming EIGRP adjacencies and injecting false routing information into the network. Both neighboring routers must have compatible authentication configuration and matching keys. Authentication does not increase bandwidth or directly change the EIGRP metric. Instead, it improves routing protocol security. In enterprise networks, this can be particularly important because an unauthorized router connected to a routing segment could otherwise potentially participate in the routing protocol.

Q204. Which EIGRP concept identifies the best route to a destination that is currently installed in the routing table?

1) Feasible successor
2) Successor
3) Query
4) Active route

Correct Answer: 2) Successor

Explanation:
In EIGRP, the successor is the best path to a particular destination and is normally installed in the IP routing table. EIGRP calculates route metrics using values such as bandwidth and delay and selects the path with the lowest feasible distance. A feasible successor is a backup path that satisfies the feasibility condition and can be used if the successor becomes unavailable. The distinction is important when troubleshooting EIGRP convergence. A successor represents the preferred route, while a feasible successor provides a loop-free alternative. If a successor fails and an eligible feasible successor is available, EIGRP can converge quickly without performing a new route query.

Q205. Which BGP attribute is primarily used to influence outbound traffic selection within an autonomous system?

1) Local Preference
2) MED
3) Origin
4) Router ID

Correct Answer: 1) Local Preference

Explanation:
BGP Local Preference is used within an autonomous system to influence which exit point should be preferred for outbound traffic. A higher Local Preference value is preferred. Because Local Preference is propagated through the iBGP environment, it can provide a consistent policy across multiple internal routers. For example, an organization with two Internet connections can assign a higher Local Preference to routes learned from the preferred provider. Internal routers will then generally select that path for outbound traffic. MED serves a different purpose, primarily influencing how external neighbors may enter an autonomous system. Understanding these attributes is important when implementing BGP traffic-engineering policies.

Q206. What is the primary purpose of a BGP prefix limit configured on a neighbor session?

1) Limit the number of routes accepted from a neighbor
2) Increase BGP hold time
3) Encrypt BGP updates
4) Disable route advertisements permanently

Correct Answer: 1) Limit the number of routes accepted from a neighbor

Explanation:
BGP prefix limits protect routers from receiving an unexpectedly large number of routes from a neighbor. An administrator can configure a maximum number of accepted prefixes for a BGP session. If the neighbor begins advertising an abnormal number of routes, the configured limit can trigger an appropriate action, depending on the configuration. This is particularly useful when connecting to service providers or other organizations because accidental route leaks can potentially overwhelm a router’s resources. Prefix limits are therefore an important operational safeguard. They do not encrypt BGP traffic or increase session timers; their primary purpose is controlling the volume of routing information accepted.

Q207. In MPLS Layer 3 VPNs, what does a Route Distinguisher primarily provide?

1) Encryption of customer traffic
2) Uniqueness for overlapping IPv4 prefixes
3) QoS classification
4) OSPF authentication

Correct Answer: 2) Uniqueness for overlapping IPv4 prefixes

Explanation:
An MPLS VPN Route Distinguisher (RD) makes customer prefixes unique within the provider’s VPN routing infrastructure. Different customers may use the same private IPv4 address space, such as 10.0.0.0/8. Without a mechanism to distinguish these identical prefixes, the provider would not be able to maintain separate VPN routing information correctly. The RD is added to an IPv4 prefix to create a VPNv4 route that is globally unique within the provider’s BGP system. The RD itself does not provide encryption. Instead, it solves the problem of overlapping address spaces. Route Targets, in contrast, control the import and export of VPN routes between VRFs.

Q208. Which MPLS VPN attribute controls which VPN routes are imported into or exported from a VRF?

1) Route Target
2) Route Distinguisher
3) MPLS TTL
4) LDP router ID

Correct Answer: 1) Route Target

Explanation:
Route Targets (RTs) are extended BGP community attributes used to control the import and export of VPN routes between VRFs. When a provider edge router exports a VPN route, it can attach one or more Route Target values to that route. Other VRFs can then be configured to import routes carrying specific Route Targets. This mechanism determines which VPNs can communicate with each other. Route Targets are different from Route Distinguishers. The RD provides uniqueness to VPNv4 routes, while the RT controls route distribution between VRFs. Correctly configuring Route Targets is therefore essential when implementing MPLS Layer 3 VPN connectivity.

Q209. Which command is most useful for verifying BGP neighbor relationships and session states?

1) show ip ospf neighbor
2) show ip eigrp neighbors
3) show ip bgp summary
4) show mpls ldp discovery

Correct Answer: 3) show ip bgp summary

Explanation:
The show ip bgp summary command provides a concise overview of BGP neighbor relationships. It displays information such as the BGP router ID, local AS number, configured neighbors, remote AS numbers, message counters, and the current BGP session state. It is one of the most commonly used commands when troubleshooting BGP adjacency problems. A numeric value in the received-prefix column generally indicates an established session, while states such as Idle or Active indicate that the session has not successfully reached the Established state. More detailed information can be obtained with commands such as show ip bgp neighbors, but the summary command is an excellent first troubleshooting step.

Q210. Which DMVPN protocol is responsible for mapping tunnel addresses to NBMA addresses?

1) OSPF
2) NHRP
3) LDP
4) SNMP

Correct Answer: 2) NHRP

Explanation:
Next Hop Resolution Protocol (NHRP) is a key component of DMVPN. It allows routers to map logical tunnel addresses to the underlying NBMA addresses used to reach remote peers. In a DMVPN environment, the hub can maintain information about spoke addresses, while spokes can dynamically discover the NBMA address of another spoke when direct communication is required. This dynamic mapping supports scalable multipoint tunnel deployments without requiring manually configured tunnels between every pair of routers. NHRP works alongside technologies such as mGRE and IPsec in DMVPN designs. Understanding NHRP mappings is especially important when troubleshooting spoke-to-spoke connectivity and DMVPN Phase 2 or Phase 3 behavior.

Q211. Which DMVPN Phase 3 feature allows the hub to inform a spoke that a better direct forwarding path exists?

1) NHRP redirect
2) NHRP registration only
3) BGP reflection
4) IPsec rekeying

Correct Answer: 1) NHRP redirect

Explanation:
NHRP redirect is an important feature of DMVPN Phase 3. When traffic initially travels through the hub toward another spoke, the hub can recognize that the destination is reachable through a more direct spoke-to-spoke path. The hub then sends an NHRP redirect message to the originating spoke. The spoke can use this information to initiate NHRP resolution and learn the appropriate direct tunnel information. This allows DMVPN Phase 3 networks to dynamically optimize forwarding paths while retaining a scalable hub-and-spoke control model. NHRP shortcut operation at the spoke complements the redirect mechanism and allows traffic to use the more efficient path.

Q212. Which IPsec protocol provides confidentiality by encrypting the payload of an IP packet?

1) AH
2) ESP
3) GRE
4) ICMP

Correct Answer: 2) ESP

Explanation:
Encapsulating Security Payload (ESP) is the IPsec protocol commonly used to provide confidentiality through encryption. ESP can also provide integrity, authentication, and anti-replay protection depending on the configured security parameters. Authentication Header (AH), in contrast, provides integrity and authentication but does not encrypt the packet payload. GRE provides tunneling but does not inherently provide encryption. In site-to-site VPN implementations, ESP is widely used because it can protect data while it traverses an untrusted network. Understanding the distinction between ESP and AH is important when troubleshooting IPsec security associations and verifying whether encryption is actually being applied to tunneled traffic.

Q213. Which QoS mechanism gives a traffic class strict priority treatment for latency-sensitive applications such as voice?

1) WRED
2) LLQ
3) FIFO
4) Traffic policing only

Correct Answer: 2) LLQ

Explanation:
Low Latency Queuing (LLQ) provides a strict-priority queue for traffic that is highly sensitive to delay and jitter. Voice traffic is a common example because excessive delay or jitter can noticeably reduce call quality. LLQ is commonly implemented as an extension of Class-Based Weighted Fair Queuing (CBWFQ), allowing selected traffic to receive priority service during congestion. The priority queue must be carefully configured because excessive priority traffic can potentially starve other classes. QoS classification determines which packets belong to the priority class, while LLQ determines how that class is serviced. This makes LLQ particularly useful for real-time applications across congested WAN links.

Q214. Which QoS mechanism assigns a DSCP value to packets so downstream devices can identify their intended treatment?

1) Marking
2) Shaping
3) Policing
4) Fragmentation

Correct Answer: 1) Marking

Explanation:
QoS marking modifies packet information to indicate the desired treatment of traffic throughout the network. For IP traffic, DSCP is commonly used as the marking mechanism. Once packets are marked, downstream routers and switches can classify them according to their DSCP values and apply appropriate queuing, scheduling, or congestion-management policies. Marking is especially useful in larger networks because classification does not need to be repeated using complex application-specific criteria at every device. For example, voice packets can be marked with an appropriate expedited-forwarding DSCP value and then receive priority treatment across the WAN. Marking therefore helps maintain consistent QoS policies throughout the network.

Q215. Which protocol is commonly used to synchronize clocks across network devices?

1) SNMP
2) Syslog
3) NTP
4) NetFlow

Correct Answer: 3) NTP

Explanation:
Network Time Protocol (NTP) is used to synchronize the clocks of network devices with a reliable time source. Accurate time synchronization is important for troubleshooting, security investigations, logging, authentication mechanisms, and event correlation. For example, if routers and servers have significantly different clocks, it can become difficult to determine the sequence of events during a network incident. NTP allows devices to obtain time from configured NTP servers and maintain clocks with appropriate synchronization. NTP is different from Syslog, which transports event messages, and SNMP, which is primarily used for monitoring and management. Accurate time is a foundational requirement for effective network operations.

Q216. Which syslog severity level represents the most serious condition?

1) 0
2) 3
3) 5
4) 7

Correct Answer: 1) 0

Explanation:
Syslog severity levels range from 0 through 7, with lower numbers representing more serious conditions. Severity level 0 is Emergency, indicating that the system is unusable and represents the most severe level. Level 1 is Alert, level 2 is Critical, level 3 is Error, level 4 is Warning, level 5 is Notice, level 6 is Informational, and level 7 is Debugging. Understanding the severity scale helps administrators configure logging appropriately. For example, a device can be configured to send messages at or above a selected severity to a centralized syslog server. This supports efficient monitoring while avoiding unnecessary log volume.

Q217. Which command can help verify the routing policy applied to an interface for policy-based routing?

1) show ip policy
2) show ip bgp summary
3) show ip ospf database
4) show mpls forwarding-table

Correct Answer: 1) show ip policy

Explanation:
The show ip policy command is useful for verifying policy-based routing configuration applied to router interfaces. Policy-based routing allows packets to be forwarded according to configured policy rather than relying solely on the normal destination-based routing table. The command can help identify which route map is applied to an interface. This is useful when troubleshooting situations where traffic is unexpectedly taking a particular path. Administrators can then inspect the corresponding route map and its match and set statements. PBR troubleshooting should also include verification of interface configuration, route-map logic, next-hop reachability, and packet forwarding behavior.

Q218. Which IPv6 address type is automatically configured on an interface and is essential for many IPv6 neighbor relationships?

1) Global unicast
2) Link-local
3) Multicast-only
4) Loopback-only

Correct Answer: 2) Link-local

Explanation:
IPv6 link-local addresses are automatically generated on IPv6-enabled interfaces and are valid only on the local network segment. They typically use the FE80::/10 prefix. Link-local addresses are extremely important because IPv6 routing protocols such as OSPFv3 can use them for neighbor communication. They are also used by several IPv6 control-plane functions, including Neighbor Discovery. Unlike global unicast addresses, link-local addresses are not routable across routers. An administrator may therefore see an IPv6 routing protocol adjacency using link-local addresses even though the network also has global IPv6 addressing. Understanding link-local behavior is essential when troubleshooting IPv6 connectivity and routing protocols.

Q219. Which command is commonly used to inspect the MPLS label forwarding entries on a Cisco router?

1) show ip arp
2) show mpls forwarding-table
3) show ip dhcp binding
4) show spanning-tree

Correct Answer: 2) show mpls forwarding-table

Explanation:
The show mpls forwarding-table command displays MPLS forwarding information, including labels and the associated forwarding actions. This is useful when troubleshooting MPLS label switching because it allows an administrator to determine how labeled packets are expected to be processed. Depending on the platform and configuration, the output can show incoming labels, outgoing labels, next hops, and interfaces. If an MPLS VPN is not forwarding correctly, examining the forwarding table can help identify whether the expected label-switched path exists. Additional commands such as show mpls ldp bindings can provide information about label distribution and bindings used by LDP.

Q220. Which BGP mechanism allows an administrator to prevent selected routes from being advertised to a neighbor?

1) Route filtering using a prefix list
2) NTP authentication
3) OSPF DR election
4) MPLS label swapping

Correct Answer: 1) Route filtering using a prefix list

Explanation:
BGP route filtering allows administrators to control which routes are advertised to or accepted from a BGP neighbor. A prefix list is one of the most common tools used for this purpose. By defining permitted and denied prefixes and applying the prefix list in the appropriate direction, an administrator can prevent selected networks from being advertised. This is important for avoiding accidental route leaks and enforcing routing policies. For example, an enterprise can permit only its own public prefixes when advertising routes to an Internet provider. Prefix lists can be combined with route maps and other BGP policy mechanisms for more advanced filtering and traffic-engineering requirements.