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Question 181

Which OSPF LSA type is originated by an ABR to describe networks within an area to other OSPF areas?

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

Correct Answer: 3

Explanation

OSPF Type 3 LSAs, also called Summary LSAs, are originated by an Area Border Router (ABR) to advertise networks from one OSPF area into another area. They allow routers in different areas to learn about inter-area destinations while maintaining the hierarchical OSPF architecture. Type 1 LSAs describe routers within an area, while Type 2 LSAs describe multiaccess networks and are originated by the DR. Type 5 LSAs advertise external routes introduced by an ASBR. Therefore, Type 3 is the correct LSA type for inter-area network advertisements.

Question 182

Which OSPF calculation algorithm determines the shortest path tree from a router’s perspective?

1. Bellman-Ford
2. Dijkstra SPF
3. Path Vector
4. Distance Vector

Correct Answer: 2

Explanation

OSPF uses the Dijkstra Shortest Path First (SPF) algorithm to calculate the shortest path tree from the router’s perspective. The calculation uses information contained in the OSPF Link-State Database (LSDB) and considers interface costs when determining paths. After calculating the shortest path tree, the router installs appropriate routes into its routing table. BGP uses a path-vector approach, while traditional distance-vector protocols use different algorithms. Therefore, Dijkstra SPF is the correct algorithm associated with OSPF path calculation.

Question 183

Which OSPF parameter is primarily used to influence the preferred path through an OSPF network?

1. Interface cost
2. Router ID
3. Area ID
4. LSA sequence number

Correct Answer: 1

Explanation

OSPF interface cost is used to influence path selection. OSPF calculates the total cost of a path by adding the costs of the interfaces along that path. When multiple routes to the same destination exist, the path with the lower total OSPF cost is generally preferred. Router ID identifies an OSPF router, Area ID identifies an OSPF area, and LSA sequence numbers help determine the freshness of link-state information. Therefore, interface cost is the correct parameter for influencing OSPF path selection.

Question 184

Which OSPF router type connects an OSPF area to another OSPF area?

1. ASBR
2. Internal router
3. ABR
4. DR

Correct Answer: 3

Explanation

An Area Border Router (ABR) connects one OSPF area to another and maintains link-state information for the areas to which it is connected. ABRs are important to OSPF’s hierarchical design because they can summarize routes between areas and help contain the scope of topology changes. An ASBR connects OSPF to external routing domains through route redistribution. An internal router has interfaces within a single area, while a DR is elected on certain multiaccess networks. Therefore, ABR is the correct router type for connecting OSPF areas.

Question 185

Which IS-IS feature allows a router to advertise routes from one IS-IS level into another level?

1. Route leaking
2. LSP flooding
3. DIS election
4. Overload bit

Correct Answer: 1

Explanation

IS-IS route leaking allows selected routes to be advertised between Level 1 and Level 2 routing domains. This can provide more granular control over which prefixes are visible across the hierarchical IS-IS topology. For example, specific Level 2 routes can be leaked into Level 1 areas when more detailed reachability information is required. LSP flooding distributes link-state information, DIS election identifies the designated intermediate system on certain networks, and the overload bit can discourage transit traffic through a router. Therefore, route leaking is correct.

Question 186

What is the primary purpose of the IS-IS Designated Intermediate System on a broadcast network?

1. Assign IP addresses
2. Reduce the number of adjacencies and LSP flooding overhead
3. Provide BGP route reflection
4. Allocate MPLS VPN labels

Correct Answer: 2

Explanation

The IS-IS Designated Intermediate System (DIS) helps reduce the amount of adjacency and link-state flooding overhead on broadcast networks. The DIS creates a pseudonode representation for the broadcast segment and originates a pseudonode LSP describing the participating routers. This approach simplifies the topology representation and reduces the need for every router to establish a full set of equivalent relationships with every other router on the segment. The DIS does not assign IP addresses, perform BGP route reflection, or allocate VPN labels. Therefore, reducing topology and flooding overhead is correct.

Question 187

Which BGP attribute indicates how a route was originally introduced into BGP?

1. MED
2. ORIGIN
3. NEXT_HOP
4. LOCAL_PREF

Correct Answer: 2

Explanation

The BGP ORIGIN attribute indicates how a route was introduced into BGP. Common origin values include IGP, EGP, and incomplete, with IGP generally preferred over EGP and incomplete during the relevant stage of BGP best-path selection. The attribute helps BGP compare otherwise eligible paths. MED influences route selection between neighboring autonomous systems, NEXT_HOP identifies the next-hop address, and LOCAL_PREF influences outbound path selection within an autonomous system. Therefore, ORIGIN is the correct attribute for identifying the route’s origin type.

Question 188

Which BGP mechanism can reduce the impact of frequent route flapping by temporarily suppressing unstable routes?

1. Route Refresh
2. Graceful Restart
3. Route Dampening
4. Add-Path

Correct Answer: 3

Explanation

BGP Route Dampening is designed to reduce the impact of unstable routes that repeatedly withdraw and reappear. When a route flaps frequently, penalties can accumulate and the route may be suppressed temporarily according to configured thresholds. This can reduce unnecessary processing and propagation of unstable routing information. Route Refresh allows routing information to be requested again, Graceful Restart helps maintain forwarding during certain restarts, and Add-Path allows multiple paths to be advertised. Therefore, Route Dampening is the correct mechanism for handling frequent route instability.

Question 189

Which BGP feature can allow a router to accept a route containing its own AS number in the AS_PATH under controlled circumstances?

1. Allowas-in
2. Next-Hop-Self
3. Local Preference
4. MED

Correct Answer: 1

Explanation

The BGP allowas-in feature allows a router to accept routes containing its own autonomous system number in the AS_PATH. Normally, BGP rejects such routes to prevent routing loops. In specific designs, such as networks using the same AS number at multiple locations, controlled use of allowas-in may be necessary. Because it weakens the normal AS_PATH loop-prevention behavior, it should be configured carefully and with appropriate policy controls. Next-Hop-Self changes the next-hop attribute, while Local Preference and MED influence path selection. Therefore, allowas-in is correct.

Question 190

Which BGP feature can provide different route policies to different peer groups while simplifying configuration?

1. BGP Communities
2. MPLS Labels
3. OSPF Areas
4. IS-IS TLVs

Correct Answer: 1

Explanation

BGP Communities allow routes to be tagged with policy information that can later be matched and acted upon by routing policies. Operators can use communities to identify routes belonging to particular customers, regions, services, or policy categories. This allows a common community value to trigger consistent actions across multiple routers or peer relationships. MPLS labels perform forwarding functions, OSPF Areas organize link-state routing, and IS-IS TLVs carry protocol information. Therefore, BGP Communities are the appropriate mechanism for simplifying policy classification and application.

Question 191

Which MPLS VPN component makes identical customer IPv4 prefixes unique within the provider’s VPN routing system?

1. Route Target
2. Route Distinguisher
3. MPLS TC
4. BGP Community

Correct Answer: 2

Explanation

A Route Distinguisher (RD) makes otherwise identical IPv4 prefixes unique within an MPLS VPN environment. For example, two customers can both use the same IPv4 prefix, but different RDs create distinct VPNv4 routes. This allows the provider to maintain overlapping customer address spaces without ambiguity in the VPN control plane. Route Targets serve a different function by controlling which VRFs import and export VPN routes. MPLS TC is related to traffic classification, while BGP Communities communicate policy information. Therefore, the Route Distinguisher is correct.

Question 192

Which MPLS VPN attribute determines whether a VPN route should be imported into a particular VRF?

1. Route Target
2. Route Distinguisher
3. MPLS TTL
4. BGP Weight

Correct Answer: 1

Explanation

Route Targets (RTs) control the import and export of VPN routes between PE routers and VRFs. An exported VPN route is associated with one or more Route Targets, and a receiving VRF imports routes whose Route Targets match its configured import policy. This provides flexible control over which customer VPN routes are reachable from a particular VRF. The Route Distinguisher makes VPN routes unique but does not determine their import policy. MPLS TTL controls packet lifetime, while BGP Weight is a local path-selection attribute. Therefore, Route Target is correct.

Question 193

Which MPLS forwarding component is responsible for associating incoming labels with outgoing labels and interfaces?

1. RIB
2. LFIB
3. ARP cache
4. LSDB

Correct Answer: 2

Explanation

The Label Forwarding Information Base (LFIB) contains the forwarding information needed to process MPLS-labeled packets. It can specify actions such as swapping an incoming label for an outgoing label, popping a label, and forwarding traffic through a particular interface or next hop. The RIB contains IP routing information, while the ARP cache contains IPv4-to-MAC mappings. An LSDB contains link-state routing information used by protocols such as OSPF or IS-IS. Therefore, LFIB is the correct component for MPLS label forwarding.

Question 194

Which MPLS OAM tool can help identify individual hops along an MPLS LSP?

1. MPLS LSP Traceroute
2. DHCP
3. SNMP SET
4. IGMP

Correct Answer: 1

Explanation

MPLS LSP Traceroute is an OAM and troubleshooting mechanism that can help identify the routers or hops involved in an MPLS Label Switched Path. It provides more detailed information than a simple connectivity test and can help operators locate where an LSP may be failing. MPLS LSP Ping can be used to test LSP connectivity, while DHCP provides host configuration, SNMP SET changes supported management objects, and IGMP handles multicast membership. Therefore, MPLS LSP Traceroute is the correct tool for identifying LSP hops.

Question 195

Which Segment Routing SID identifies a specific node or its associated prefix in the network?

1. Node-SID
2. Adj-SID
3. Binding SID
4. Service SID

Correct Answer: 1

Explanation

A Node-SID identifies a node in a Segment Routing domain and is commonly associated with the node’s loopback or another advertised prefix. When a packet is instructed to follow a Node-SID, the network forwards it toward the corresponding node according to the Segment Routing topology. An Adj-SID represents a specific adjacency, while a Binding SID can represent a segment-routing policy or set of instructions. Service SIDs are associated with service-specific functions in relevant Segment Routing architectures. Therefore, Node-SID is the correct answer.

Question 196

What is the primary purpose of a Binding SID in Segment Routing Traffic Engineering?

1. Identify an SNMP object
2. Represent an SR policy as a segment
3. Identify an OSPF area
4. Allocate an IPv4 address

Correct Answer: 2

Explanation

A Binding Segment Identifier (BSID) can represent a Segment Routing policy as a single segment. When traffic is steered using the BSID, the associated SR policy can determine the sequence of segments that should be applied to the traffic. This abstraction simplifies policy invocation because an external mechanism does not necessarily need to know the entire internal segment list. BSIDs are therefore useful in SR Traffic Engineering and policy-based forwarding. They are unrelated to SNMP objects, OSPF area identifiers, or IPv4 address allocation. Therefore, representing an SR policy as a segment is correct.

Question 197

Which QoS scheduling mechanism assigns bandwidth to multiple traffic classes according to configured weights?

1. CBWFQ
2. LLQ
3. Policing
4. WRED

Correct Answer: 1

Explanation

Class-Based Weighted Fair Queuing (CBWFQ) allows administrators to define traffic classes and allocate bandwidth to those classes during congestion. Each class can be configured with bandwidth or other scheduling parameters, enabling predictable resource allocation among different traffic types. LLQ adds a strict priority queue for delay-sensitive traffic, while policing enforces traffic-rate limits. WRED is a congestion-avoidance mechanism that can selectively drop packets before a queue becomes full. Therefore, CBWFQ is the appropriate scheduling mechanism for allocating bandwidth among configured traffic classes.

Question 198

Which QoS mechanism is specifically designed to provide strict priority service to a selected traffic class?

1. WRED
2. LLQ
3. CBWFQ
4. Shaping

Correct Answer: 2

Explanation

Low Latency Queuing (LLQ) provides a strict priority queue for selected traffic classes. This is particularly useful for real-time applications such as voice and other delay-sensitive traffic. During congestion, packets in the priority queue receive preferential service, helping reduce latency and jitter. CBWFQ provides bandwidth-based scheduling for classes but does not inherently provide the same strict priority treatment. WRED manages congestion through selective packet dropping, while shaping controls the transmission rate. Therefore, LLQ is the correct QoS mechanism for strict priority service.

Question 199

Which multicast routing protocol is commonly used to build multicast distribution trees independently of the underlying unicast routing protocol?

1. PIM
2. LACP
3. LDP
4. BFD

Correct Answer: 1

Explanation

Protocol Independent Multicast (PIM) uses the existing unicast routing table for Reverse Path Forwarding decisions while providing multicast routing functionality. It is called protocol independent because it can operate with different underlying unicast routing protocols, such as OSPF, IS-IS, or BGP. PIM has multiple operating modes, including Sparse Mode and Source-Specific Multicast. LACP provides link aggregation, LDP distributes MPLS labels, and BFD provides rapid failure detection. Therefore, PIM is the correct multicast routing protocol in this scenario.

Question 200

Which multicast feature allows a receiver to join a multicast stream for a specific source rather than using a shared Rendezvous Point tree?

1. PIM-DM
2. Anycast-RP
3. SSM
4. MSDP

Correct Answer: 3

Explanation

Source-Specific Multicast (SSM) allows receivers to request multicast traffic from a specific source and multicast group. This creates a source-specific channel and eliminates the need for a traditional shared-tree Rendezvous Point architecture for the multicast flow. SSM is commonly associated with IGMPv3 for IPv4 and MLDv2 for IPv6 receiver signaling. Anycast-RP provides redundant Rendezvous Points, MSDP exchanges multicast source information, and PIM-DM uses dense-mode forwarding behavior. Therefore, SSM is the correct multicast feature for source-specific stream selection.