View Full Cisco CCNP Service Provider 300-510 Exam Dumps and Practice Test Dumps

 

Question 321. A provider is troubleshooting an IS-IS network and discovers that a Level-1 router cannot reach destinations outside its local area. The router has no specific route for those destinations. Which behavior should normally provide connectivity?

1. The router should use an OSPF Type 5 LSA
2. The router should establish an eBGP session
3. The router should use an MPLS VPN label
4. The router should use a default route toward a Level-1-2 router

Correct Answer: 4. The router should use a default route toward a Level-1-2 router

Explanation :-

IS-IS Level-1 routers maintain detailed routing information for their local area but do not maintain the complete Level-2 topology. Level-1-2 routers connect the Level-1 area to the Level-2 backbone. A Level-1 router can therefore use a default route toward an appropriate Level-1-2 router for destinations outside its local area. This avoids requiring the Level-1 router to maintain complete inter-area topology information. OSPF Type 5 LSAs, eBGP sessions, and MPLS VPN labels are unrelated to the normal IS-IS Level-1 forwarding mechanism. Therefore, the expected solution is a default route toward a Level-1-2 router.

Question 322. An OSPF administrator wants to advertise a summarized set of routes from one area into another while minimizing the number of Type 3 LSAs. Which feature should be configured on the ABR?

1. Area range
2. Virtual link
3. Router priority
4. Passive interface

Correct Answer: 1. Area range

Explanation :-

An OSPF ABR can use an area range to summarize multiple prefixes belonging to an area before advertising them as inter-area routes. This reduces the number of individual Type 3 Summary LSAs that need to be propagated into other areas. Summarization can also reduce routing-table size and limit the impact of changes to individual prefixes within the summarized range. A virtual link is used for logical connectivity to the backbone, router priority influences DR/BDR election, and passive-interface controls adjacency formation on an interface. Therefore, area range is the appropriate feature for inter-area route summarization.

Question 323. A BGP router receives the same prefix from an eBGP peer and an iBGP peer. Assuming earlier best-path attributes are equivalent, which path is normally preferred?

1. The iBGP path
2. The path with the higher MED
3. The eBGP path
4. The path with the longer AS_PATH

Correct Answer: 3. The eBGP path

Explanation :-

BGP best-path selection includes a preference for an eBGP-learned route over an iBGP-learned route at the appropriate stage of the selection process, assuming the relevant earlier attributes are equivalent and the routes are otherwise eligible. This distinction is important in provider networks where the same destination may be learned from both internal and external BGP peers. LOCAL_PREF, Weight on Cisco platforms, and other earlier attributes can override the comparison if they differ. MED and AS_PATH are evaluated at different stages. Under the conditions stated, the eBGP-learned path is preferred.

Question 324. A service provider wants to make traffic entering its autonomous system prefer one of two available links. The provider cannot directly control the neighbor’s LOCAL_PREF. Which outbound advertisement technique can influence the neighbor’s path selection?

1. Increase local Weight
2. AS_PATH prepending
3. Increase internal LOCAL_PREF
4. Enable BFD

Correct Answer: 2. AS_PATH prepending

Explanation :-

AS_PATH prepending can influence how a neighboring autonomous system selects an inbound path. By adding additional copies of the provider’s AS number to an advertised route, the provider can make that path appear to have a longer AS_PATH. If the neighbor’s earlier path-selection attributes do not override AS_PATH, the neighbor may prefer another available path. LOCAL_PREF is generally controlled inside the receiving AS and is therefore not directly controlled by the advertising provider. Cisco Weight is local to a router, while BFD provides failure detection. Thus, AS_PATH prepending is a common inbound traffic-engineering technique.

Question 325. A PE router has two customer VRFs with overlapping IPv4 prefixes. Which MPLS VPN component allows the identical IPv4 prefixes to coexist as distinct VPN routes in MP-BGP?

1. Route Target
2. VPN label
3. LOCAL_PREF
4. Route Distinguisher

Correct Answer: 4. Route Distinguisher

Explanation :-

The Route Distinguisher (RD) is used to make otherwise identical customer IPv4 prefixes unique in the VPNv4 address family. For example, two customers can both advertise 10.10.10.0/24, and different RDs allow those prefixes to become distinct VPNv4 routes. Route Targets have a different purpose: they control which VRFs import and export VPN routes. VPN labels are used for forwarding traffic to the appropriate VRF or service, while LOCAL_PREF is a BGP path-selection attribute. Therefore, the RD is the component that provides uniqueness for overlapping customer prefixes.

Question 326. An MPLS L3VPN route is present in the VPNv4 BGP table, but the receiving PE does not install it into the customer’s VRF. The VPN route has the correct RD but an unexpected RT. What should be investigated?

1. OSPF DR election
2. LDP router ID
3. VRF import Route Target
4. BGP router ID only

Correct Answer: 3. VRF import Route Target

Explanation :-

The Route Distinguisher makes a VPN prefix unique but does not determine whether the route is imported into a particular VRF. Route Target extended communities control VPN route import and export policy. If the route’s RT does not match an import RT configured under the destination VRF, the PE can retain the route in the VPNv4 BGP table while excluding it from that VRF. This is a common L3VPN troubleshooting scenario. OSPF DR election and LDP router ID do not determine VRF import policy. Therefore, the VRF’s import Route Target configuration should be examined.

Question 327. A BGP route reflector has several clients and receives a route from one client. Which mechanism helps prevent the route from being reflected repeatedly between route reflectors in the same cluster?

1. CLUSTER_LIST
2. MED
3. LOCAL_PREF
4. Weight

Correct Answer: 1. CLUSTER_LIST

Explanation :-

The CLUSTER_LIST attribute is used by BGP route reflectors to help prevent routing loops involving route-reflector clusters. When a route reflector reflects a route, it adds its cluster ID to the CLUSTER_LIST. If a route reflector later receives a route containing its own cluster ID, it can reject the route to prevent a reflection loop. ORIGINATOR_ID provides information about the router that originally generated the route, while LOCAL_PREF, MED, and Weight are primarily path-selection attributes. Therefore, CLUSTER_LIST is the key loop-prevention mechanism among the listed choices.

Question 328. A provider wants to detect a forwarding failure between two routers quickly, independent of the normal BGP keepalive interval. Which protocol should be deployed?

1. RSVP-TE
2. BFD
3. MSDP
4. LDP

Correct Answer: 2. BFD

Explanation :-

Bidirectional Forwarding Detection (BFD) is designed for rapid detection of forwarding-path failures. It can operate independently of the slower keepalive and hold timers used by routing protocols and can be integrated with protocols such as BGP. When a BFD session detects a failure, the associated routing protocol can respond quickly according to the configured integration. RSVP-TE provides MPLS traffic engineering, LDP distributes MPLS labels, and MSDP distributes multicast source information. Therefore, BFD is the appropriate protocol when fast forwarding-failure detection is required.

Question 329. An OSPF router in an NSSA receives an external route redistributed by another router inside the same NSSA. Which LSA type represents the route inside the NSSA?

1. Type 3
2. Type 5
3. Type 7
4. Type 4

Correct Answer: 3. Type 7

Explanation :-

NSSA areas allow external routes to be introduced while restricting normal Type 5 external LSAs from entering the area. A router redistributing an external route inside an NSSA represents that route using a Type 7 LSA. The NSSA ABR can translate eligible Type 7 information into Type 5 LSAs when advertising the external route into the broader OSPF domain. Type 3 LSAs represent inter-area network information, Type 4 LSAs describe reachability to ASBRs, and Type 5 LSAs normally represent external routes outside an NSSA. Therefore, Type 7 is correct inside the NSSA.

Question 330. A BGP administrator wants to prevent a customer’s route from being advertised to any other BGP neighbor after it is received. Which well-known community should be applied?

1. NO_EXPORT
2. NOPEER
3. LOCAL_PREF
4. NO_ADVERTISE

Correct Answer: 4. NO_ADVERTISE

Explanation :-

The NO_ADVERTISE well-known BGP community tells a BGP speaker not to advertise the associated route to any BGP peer. This is more restrictive than NO_EXPORT, which is intended to prevent propagation outside the local autonomous system or confederation boundary while permitting appropriate internal distribution. LOCAL_PREF is used to influence outbound path selection and is not a propagation restriction. NOPEER has different standardized semantics and is not the normal answer when the explicit requirement is to prohibit advertisement to any BGP peer. Therefore, NO_ADVERTISE satisfies the stated requirement.

Question 331. An IS-IS router receives a CSNP indicating that a newer LSP exists than the copy currently stored in its database. What should the router normally request?

1. A BGP UPDATE
2. The newer LSP using a PSNP
3. An OSPF LSA
4. An MPLS label binding

Correct Answer: 2. The newer LSP using a PSNP

Explanation :-

IS-IS uses Complete Sequence Number PDUs (CSNPs) to describe the LSP database information known by a router. If a router determines from a CSNP that it is missing a newer LSP, it can use a Partial Sequence Number PDU (PSNP) to request the required LSP. This allows neighboring IS-IS routers to synchronize their link-state databases. BGP UPDATE messages, OSPF LSAs, and MPLS label bindings belong to different protocols and do not perform IS-IS database synchronization. Therefore, the appropriate request is a PSNP identifying the needed newer LSP.

Question 332. A provider wants to distribute only a selected subset of customer prefixes into an upstream BGP session. Which configuration combination is most directly suited for this purpose?

1. Prefix list and routing policy
2. BFD and LDP
3. Route Target and RD
4. OSPF router priority and area range

Correct Answer: 1. Prefix list and routing policy

Explanation :-

Prefix lists and routing policies can be combined to precisely control which routes are accepted or advertised through a BGP session. A prefix list defines the prefixes or prefix ranges of interest, while the routing policy determines how those matches are handled, such as permitting or rejecting them. This combination is widely used for customer-route filtering and route-leak prevention. Route Targets and RDs are primarily associated with MPLS VPNs, while BFD and LDP address failure detection and label distribution. OSPF router priority and area range solve different OSPF problems. Therefore, prefix lists and routing policies are appropriate.

Question 333. A Segment Routing policy contains several candidate paths. The operator wants one candidate path to be selected over another when both are valid. Which parameter can influence this selection?

1. BGP Weight
2. OSPF router priority
3. Candidate-path preference
4. IS-IS area address

Correct Answer: 3. Candidate-path preference

Explanation :-

Segment Routing policies can contain multiple candidate paths, allowing different path definitions or sources to be available for the same policy. Candidate-path preference is used to determine which valid candidate path should be selected according to the SR policy selection rules. This enables operators to define preferred and fallback path choices. BGP Weight is a local BGP path-selection attribute, OSPF router priority influences DR/BDR elections, and an IS-IS area address identifies an IS-IS area. Therefore, candidate-path preference is the relevant SR Policy parameter for influencing selection among valid candidates.

Question 334. A multicast router receives traffic from source S for group G, but the incoming interface is not the interface selected by the unicast routing table toward S. What is the expected result?

1. The router immediately creates a PIM BSR election
2. The router converts the traffic into an SSM stream
3. The router performs an RPF check and may discard the traffic
4. The router automatically forwards the traffic to every PIM neighbor

Correct Answer: 3. The router performs an RPF check and may discard the traffic

Explanation :-

PIM routers use Reverse Path Forwarding checks to validate the incoming interface for multicast traffic. The router compares the received interface with the interface that the unicast routing table selects as the reverse path toward the multicast source. If the packet arrives on an interface that is not the expected RPF interface, the router can reject the packet rather than forwarding it normally. This prevents multicast forwarding loops and incorrect duplicate paths. BSR is related to RP discovery, SSM is a multicast service model, and PIM does not automatically flood traffic to every neighbor.

Question 335. A customer requires IPv6 connectivity across an MPLS provider network where the provider core does not need to run IPv6 in the IGP. Which technology can transport IPv6 unicast routes using MP-BGP over an MPLS IPv4 core?

1. 6PE
2. PIM-SM
3. LDP targeted session
4. OSPFv3 virtual link

Correct Answer: 1. 6PE

Explanation :-

6PE enables IPv6 provider-edge routers to transport IPv6 unicast traffic across an MPLS network whose core can remain IPv4-based. IPv6 routes are exchanged using MP-BGP, while MPLS labels provide transport across the provider core. This allows the provider to introduce IPv6 services without requiring every core router to run IPv6 routing. PIM-SM is a multicast routing protocol, targeted LDP establishes label-distribution relationships under specific circumstances, and an OSPFv3 virtual link does not provide the described IPv6-over-MPLS service architecture. Therefore, 6PE is the appropriate technology.

Question 336. A BGP router is configured with a maximum-prefix limit for a customer session. The customer unexpectedly advertises more prefixes than the configured threshold. What is the primary purpose of this feature?

1. Increase BGP path diversity
2. Protect the router from excessive route reception
3. Improve MPLS label distribution
4. Select a preferred outbound path

Correct Answer: 2. Protect the router from excessive route reception

Explanation :-

The BGP maximum-prefix feature protects a router by limiting the number of prefixes it will accept from a BGP neighbor. If the received prefix count exceeds the configured threshold, the router can take protective action according to the configured implementation and options. This helps reduce the impact of accidental route leaks, misconfiguration, or unexpectedly large routing tables. Maximum-prefix does not increase BGP path diversity, distribute MPLS labels, or directly select an outbound path. Therefore, its primary purpose is protection against excessive route reception.

Question 337. A service provider wants to use a single multicast RP address while deploying two RP routers for redundancy. Both RP routers advertise the same logical RP address. Which design is commonly used?

1. PIM Assert
2. IGMP Snooping
3. BGP Add-Path
4. Anycast RP

Correct Answer: 4. Anycast RP

Explanation :-

Anycast RP allows multiple physical RP routers to share the same logical RP address. Multicast routers can select the appropriate RP instance based on the unicast routing topology, providing redundancy and potentially improving geographic distribution of RP services. MSDP can be used between Anycast RP routers to synchronize information about multicast sources in traditional ASM deployments. PIM Assert addresses duplicate forwarding on shared segments, IGMP Snooping operates at Layer 2, and BGP Add-Path is unrelated to multicast RP redundancy. Therefore, Anycast RP is the appropriate design for providing redundant RP instances under one logical address.

Question 338. A provider wants to ensure that a route learned from an eBGP peer is not advertised outside the local autonomous system while still permitting internal distribution. Which BGP community is appropriate?

1. NO_EXPORT
2. NO_ADVERTISE
3. Additive
4. ORIGIN

Correct Answer: 1. NO_EXPORT

Explanation :-

NO_EXPORT is a well-known BGP community used to restrict route propagation beyond the local autonomous system or confederation boundary according to standard BGP community behavior. The route can still be distributed internally when appropriate. NO_ADVERTISE is more restrictive because it prevents advertisement to BGP peers. Additive is a policy keyword controlling whether a community is appended to an existing set, while ORIGIN is a BGP path attribute used in route selection. Therefore, NO_EXPORT matches the requirement to permit internal propagation while preventing external advertisement.

Question 339. An MPLS transit router has an incoming label binding but does not have the corresponding entry in its LFIB. What forwarding behavior is affected?

1. BGP route-reflector operation
2. MPLS label-switched forwarding
3. OSPF DR election
4. PIM RP discovery

Correct Answer: 2. MPLS label-switched forwarding

Explanation :-

The LFIB contains the forwarding information used to process labeled packets in the data plane. A router may have label information in the LIB, but the relevant information must be installed or programmed into the forwarding structure before labeled traffic can be switched correctly. If a required LFIB entry is missing, the router may be unable to perform the expected label operation, such as swap, pop, or push, for the corresponding FEC. BGP route reflection, OSPF DR election, and PIM RP discovery operate independently of the MPLS LFIB forwarding table. Therefore, MPLS label-switched forwarding is directly affected.

Question 340. A BGP engineer wants to preserve multiple valid paths for a prefix on downstream routers to improve path diversity and convergence options. Which feature should be considered?

1. BGP route dampening
2. BGP conditional advertisement
3. BGP Add-Path
4. BGP community stripping

Correct Answer: 3. BGP Add-Path

Explanation :-

BGP Add-Path allows a BGP speaker to advertise multiple paths for the same prefix rather than advertising only one selected best path. This can give downstream routers additional path choices and can improve path diversity in suitable service-provider designs. It is particularly useful where retaining alternate paths can support faster convergence or traffic-engineering requirements. Route dampening addresses route instability, conditional advertisement controls announcements according to routing conditions, and community stripping modifies BGP policy information. Therefore, Add-Path is the feature that directly supports advertising multiple valid paths for the same prefix.