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

 

Question 341. An IS-IS router receives an LSP with a higher sequence number than the copy in its local database. What should the router normally do?

1. Delete all existing IS-IS adjacencies
2. Install the newer LSP and flood it as appropriate
3. Ignore the LSP until the current LSP expires
4. Convert the LSP into an OSPF LSA

Correct Answer: 2. Install the newer LSP and flood it as appropriate

Explanation :-

IS-IS uses LSP sequence numbers to determine the relative freshness of link-state information. When a router receives an LSP with a higher sequence number than the version stored locally, the received LSP represents newer information. The router updates its link-state database and floods the newer LSP through the appropriate interfaces so other routers can synchronize their databases. It does not need to tear down its adjacencies simply because a newer LSP arrived. OSPF LSAs and BGP updates are separate protocol mechanisms. Therefore, installing and appropriately flooding the newer LSP is the expected IS-IS behavior.

Question 342. A provider has several internal prefixes that should be advertised as one summarized route from an OSPF area into the backbone. Which configuration feature should be used on the ABR?

1. OSPF passive-interface
2. OSPF router priority
3. OSPF virtual link
4. OSPF area range

Correct Answer: 4. OSPF area range

Explanation :-

An OSPF ABR can use an area range to summarize multiple prefixes from an area into a larger address range when advertising them to other areas. This reduces the number of inter-area routes and associated Type 3 Summary LSAs. It can also reduce routing-table size and limit the impact of changes to individual component prefixes. Passive-interface controls adjacency formation, router priority influences DR/BDR elections on multiaccess networks, and virtual links provide logical connectivity to the backbone. Therefore, area range is the appropriate feature for summarizing internal prefixes at an OSPF ABR.

Question 343. A BGP router must ensure that a route learned from one iBGP peer can be advertised to another iBGP peer without creating a full iBGP mesh. Which feature provides this capability?

1. Route reflection
2. MED
3. BGP dampening
4. AS_PATH prepending

Correct Answer: 1. Route reflection

Explanation :-

By default, an iBGP router does not advertise routes learned from one iBGP peer to another iBGP peer. This iBGP split-horizon behavior prevents routing loops but traditionally requires a full mesh of iBGP sessions. Route reflection provides a scalable alternative by allowing a route reflector to receive routes from clients and reflect eligible routes to other clients. Additional attributes such as ORIGINATOR_ID and CLUSTER_LIST help prevent reflection loops. MED, dampening, and AS_PATH prepending serve different purposes and do not remove the iBGP split-horizon limitation. Therefore, route reflection is the appropriate solution.

Question 344. A service provider has two external exit points and wants routers throughout the AS to prefer one exit for outbound traffic. Which BGP attribute should normally be assigned a higher value for the preferred path?

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

Correct Answer: 3. LOCAL_PREF

Explanation :-

LOCAL_PREF is an internal BGP attribute used to influence which exit point an autonomous system prefers for outbound traffic. Higher LOCAL_PREF values are preferred during BGP best-path selection. Because the attribute is distributed within the AS through BGP, it can provide consistent outbound path preference across multiple routers. AS_PATH is primarily used to represent the autonomous systems traversed by a route, MED can influence neighboring AS path selection under applicable conditions, and ORIGIN is considered later in the best-path process. Therefore, increasing LOCAL_PREF on the desired exit path is the standard approach for outbound traffic engineering.

Question 345. A PE router receives two VPNv4 routes containing identical customer IPv4 prefixes but different RDs. What allows both routes to coexist in the MP-BGP table?

1. Route Target
2. Route Distinguisher
3. BGP Weight
4. MED

Correct Answer: 2. Route Distinguisher

Explanation :-

The Route Distinguisher makes overlapping customer prefixes unique in the VPNv4 address family. Two customers can use the same IPv4 prefix, such as 192.0.2.0/24, while different RDs create distinct VPNv4 route identities. This allows those routes to coexist in MP-BGP. Route Targets perform a separate function by controlling which VRFs import or export VPN routes. Weight and MED are BGP path-selection attributes and do not provide VPN prefix uniqueness. Therefore, the Route Distinguisher is the component responsible for distinguishing otherwise identical customer prefixes.

Question 346. A BGP administrator wants a route to remain available within the local AS but prevents the route from being advertised to external autonomous systems. Which community should be applied?

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

Correct Answer: 1. NO_EXPORT

Explanation :-

NO_EXPORT is a well-known BGP community that limits propagation beyond the local autonomous system or confederation boundary according to standard BGP behavior. This allows the route to remain usable and distributable within the local AS while restricting external advertisement. NO_ADVERTISE is more restrictive because it tells a BGP speaker not to advertise the route to any BGP peer. Additive is used when adding a community without replacing existing communities, while ORIGIN is a path attribute involved in best-path selection. Therefore, NO_EXPORT is the appropriate community for the stated propagation requirement.

Question 347. A provider wants to advertise a specific route through BGP only if another route is absent from the routing information base. Which BGP capability is designed for this scenario?

1. BGP Add-Path
2. BGP maximum-prefix
3. BGP route dampening
4. BGP conditional advertisement

Correct Answer: 4. BGP conditional advertisement

Explanation :-

BGP conditional advertisement allows route announcements to depend on the presence or absence of another route or specified condition. This can be useful when a provider wants to advertise a backup route only when a preferred path becomes unavailable. The feature provides a policy-driven mechanism for controlling route advertisement based on routing state. Add-Path provides multiple path advertisements, maximum-prefix protects a BGP session from receiving excessive routes, and dampening is intended to reduce the impact of unstable routes. Therefore, conditional advertisement is the capability that directly supports the described conditional route announcement.

Question 348. An MPLS router receives a packet with an incoming label that must be removed before the packet is sent toward the egress router. Which operation removes the top MPLS label?

1. Push
2. Swap
3. Pop
4. Route reflection

Correct Answer: 3. Pop

Explanation :-

An MPLS pop operation removes the top label from the MPLS label stack. This can occur as part of normal MPLS forwarding or through penultimate-hop popping, depending on the label operation programmed in the LFIB. A swap replaces the incoming top label with another outgoing label, while push adds a new label to the packet. Route reflection is a BGP control-plane mechanism and has no role in MPLS label operations. Therefore, when the requirement is specifically to remove the top MPLS label, the correct operation is pop.

Question 349. A customer wants to use the same IPv4 prefix in multiple VPNs. Which MPLS VPN component ensures the prefixes remain distinguishable when exchanged through MP-BGP?

1. Route Target
2. Route Distinguisher
3. BFD
4. PIM Assert

Correct Answer: 2. Route Distinguisher

Explanation :-

The Route Distinguisher extends an IPv4 prefix into a unique VPNv4 address so that overlapping customer prefixes can coexist in the provider’s MP-BGP routing table. Different VPNs can therefore advertise the same IPv4 prefix without the routes being treated as identical. Route Targets serve as import and export policy identifiers, determining which VRFs should receive a VPN route. BFD provides failure detection, while PIM Assert resolves multicast forwarding competition on shared segments. Therefore, the Route Distinguisher provides the required VPN prefix uniqueness.

Question 350. A provider uses Segment Routing Traffic Engineering and defines multiple valid candidate paths for the same SR Policy. Which parameter determines the relative preference among candidate paths?

1. OSPF cost only
2. BGP MED
3. MPLS VPN label
4. Candidate-path preference

Correct Answer: 4. Candidate-path preference

Explanation :-

Segment Routing policies can contain multiple candidate paths, allowing an operator to define alternatives for a given policy. Candidate-path preference is used as part of the selection process to determine which valid candidate should be active. This makes it possible to establish preferred and fallback paths without relying solely on the underlying IGP shortest path. OSPF cost can influence underlying topology calculations, but it is not the direct SR Policy candidate-path preference parameter. BGP MED and MPLS VPN labels serve different functions. Therefore, candidate-path preference is the appropriate answer.

Question 351. An IS-IS router receives a CSNP and determines that it is missing an LSP advertised by its neighbor. Which PDU can be used to request the missing LSP?

1. Hello PDU
2. LSP acknowledgment only
3. PSNP
4. BGP UPDATE

Correct Answer: 3. PSNP

Explanation :-

IS-IS uses Complete Sequence Number PDUs to describe the contents of an LSP database. If a router identifies a missing LSP from the CSNP information, it can use a Partial Sequence Number PDU (PSNP) to request that specific LSP from its neighbor. PSNPs therefore participate in database synchronization and reliable LSP exchange. Hello PDUs establish and maintain IS-IS adjacencies, while BGP UPDATE messages belong to BGP. Therefore, PSNP is the appropriate PDU for requesting missing LSP information identified through CSNP processing.

Question 352. A service provider wants to prevent customer routes with unexpected prefixes from being accepted through an eBGP session. Which mechanism provides explicit prefix-based filtering?

1. BFD
2. Prefix list
3. Route Target
4. SR Node SID

Correct Answer: 2. Prefix list

Explanation :-

A prefix list provides explicit filtering based on network prefixes and prefix lengths. It can be referenced by a BGP routing policy to permit or deny routes received from or advertised to a neighbor. This makes prefix lists a fundamental tool for customer-route filtering and route-leak prevention in service-provider networks. BFD provides rapid failure detection, Route Targets control MPLS VPN route import and export, and an SR Node SID identifies a Segment Routing node. Therefore, when the requirement is to filter routes according to their prefixes, a prefix list is the appropriate mechanism.

Question 353. An MPLS L3VPN customer route is correctly present in MP-BGP, but the remote PE does not import it into the customer’s VRF. Which attribute should be compared with the VRF import configuration?

1. MED
2. AS_PATH
3. Route Distinguisher
4. Route Target

Correct Answer: 4. Route Target

Explanation :-

Route Targets determine whether a VPN route should be imported into a particular VRF. When troubleshooting an MPLS L3VPN route that exists in the VPNv4 BGP table but is missing from a VRF, the engineer should compare the route’s Route Target extended communities with the VRF’s configured import RTs. The RD provides route uniqueness but does not determine import membership. AS_PATH and MED are BGP path attributes and do not define the VRF’s import policy. Therefore, comparing the route’s RT with the VRF import Route Target configuration is the correct troubleshooting step.

Question 354. A BGP route should be accepted from a customer only when its prefix matches a specific approved prefix range. Which combination provides granular control over the accepted prefixes?

1. Prefix list and BGP routing policy
2. BFD and OSPF authentication
3. Route Target and VPN label
4. IS-IS metric and SRGB

Correct Answer: 1. Prefix list and BGP routing policy

Explanation :-

A prefix list can define the exact prefixes and prefix lengths that are permitted or denied. A BGP routing policy can then reference those matches and determine the resulting action, such as accepting, rejecting, or modifying the route. This combination provides granular control over customer advertisements and is commonly used to prevent accidental route leaks. BFD handles failure detection, Route Targets and VPN labels belong to MPLS VPN operation, and IS-IS metrics and SRGB values serve different routing and Segment Routing purposes. Therefore, prefix lists combined with routing policy provide the required filtering control.

Question 355. A PIM-SM deployment requires dynamic discovery and distribution of Rendezvous Point information. Which mechanism performs this role?

1. MSDP
2. IGMPv3
3. BSR
4. BFD

Correct Answer: 3. BSR

Explanation :-

The PIM Bootstrap Router mechanism provides dynamic distribution of Rendezvous Point information within a PIM-SM domain. Candidate RPs advertise their information, and the BSR distributes the resulting RP information to PIM routers. This allows routers to determine which RP is associated with multicast groups without requiring every router to have manually configured RP mappings. MSDP can exchange source information between RPs, IGMPv3 provides receiver membership and source-filtering information, and BFD detects forwarding failures. Therefore, BSR is the mechanism responsible for dynamic PIM-SM RP information distribution.

Question 356. A router receives an MPLS packet and replaces the incoming label with a different outgoing label according to its LFIB. Which operation has occurred?

1. Push
2. Swap
3. Pop
4. PHP

Correct Answer: 2. Swap

Explanation :-

An MPLS swap operation replaces the top incoming label with another label specified by the router’s LFIB. Transit LSRs commonly perform label swapping as packets move through an MPLS label-switched path. Push adds a label, while pop removes a label. PHP is a particular form of label removal normally performed by the penultimate router before the egress LSR. Therefore, when an incoming label is replaced with a different outgoing label, the operation is a label swap.

Question 357. A BGP router receives a route from an eBGP neighbor but the next-hop address is unreachable through the local routing table. What is the likely consequence?

1. The BGP route may not be installed as usable
2. The route automatically becomes a default route
3. The router changes the AS_PATH automatically
4. The route is automatically imported into every VRF

Correct Answer: 1. The BGP route may not be installed as usable

Explanation :-

BGP requires recursive reachability to the next-hop address before a route can normally be installed and used for forwarding. A route may appear in BGP information while remaining unusable if the next-hop cannot be resolved through the routing table. This is why BGP next-hop reachability is a critical troubleshooting consideration. BGP does not automatically convert an unreachable route into a default route, alter its AS_PATH to fix the problem, or import it into every VRF. Therefore, an unreachable next hop can prevent the BGP route from becoming a usable forwarding entry.

Question 358. A service provider wants a Segment Routing segment to force traffic over a particular physical adjacency instead of simply forwarding toward a node using the shortest path. Which SID is appropriate?

1. Node SID
2. Binding SID
3. VPN label
4. Adjacency SID

Correct Answer: 4. Adjacency SID

Explanation :-

An Adjacency SID represents a specific link or adjacency and provides fine-grained control over the path traffic takes through a Segment Routing network. When an Adjacency SID is included in a segment list, traffic can be explicitly directed over that particular adjacency. A Node SID normally represents reachability toward a node using the applicable shortest-path behavior, while a Binding SID identifies an SR Policy or segment-list construct. A VPN label is unrelated to SR link steering. Therefore, an Adjacency SID is the appropriate choice for forcing traffic across a particular link.

Question 359. A multicast router has multiple possible paths toward a source and receives multicast packets on an interface that is not the expected reverse path. Which process determines whether the packets should be accepted?

1. PIM BSR election
2. MSDP source registration
3. RPF check
4. BGP best-path selection

Correct Answer: 3. RPF check

Explanation :-

The Reverse Path Forwarding check determines whether multicast traffic arrives on the interface that the router considers the correct path back toward the multicast source. The router uses its unicast routing information to determine the expected reverse-path interface. If multicast packets arrive on a different interface, the RPF check can fail and the traffic may be discarded. BSR handles RP discovery, MSDP distributes multicast source information between appropriate PIM domains or RPs, and BGP best-path selection is unrelated to multicast packet acceptance. Therefore, the RPF check determines whether the incoming multicast path is valid.

Question 360. A provider wants to advertise several paths for the same BGP prefix to a downstream router so that the downstream router can retain additional path choices. Which feature provides this capability?

1. BGP route dampening
2. BGP maximum-prefix
3. BGP Add-Path
4. BGP conditional advertisement

Correct Answer: 3. BGP Add-Path

Explanation :-

BGP Add-Path allows a BGP speaker to advertise more than one path for the same prefix instead of limiting the advertisement to only the selected best path. This provides downstream routers with additional path diversity and can support improved convergence and traffic-engineering designs. Route dampening is intended to suppress unstable routes, maximum-prefix limits the number of routes received from a neighbor, and conditional advertisement makes route announcements dependent on specified routing conditions. Therefore, BGP Add-Path directly provides the multiple-path advertisement capability required in this scenario.