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

 

Question 281. A service provider uses IS-IS, and a router receives an LSP with a sequence number newer than the copy in its local database. What should the router do?

1. Ignore the newer LSP until the current LSP expires
2. Replace the newer LSP with its locally stored version
3. Immediately remove all Level-2 adjacencies
4. Update its database and flood the newer LSP to appropriate neighbors

Correct Answer: 4. Update its database and flood the newer LSP to appropriate neighbors

Explanation :-

IS-IS uses sequence numbers to determine which copy of an LSP is newer. When a router receives an LSP with a higher sequence number than the version in its database, it updates its local link-state database with the newer information. The router then floods the updated LSP through the appropriate IS-IS interfaces so other routers can synchronize their databases. This mechanism allows IS-IS to maintain consistent topology information throughout the routing domain. Older LSP copies are not preferred over a newer sequence number, and the router does not need to reset its adjacencies simply because it received newer topology information.

Question 282. An OSPF area contains many prefixes that are summarized by an ABR. Which configuration feature can reduce the number of inter-area routes advertised into another area?

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

Correct Answer: 2. Area range summarization

Explanation :-

OSPF ABRs can use area range summarization to combine multiple specific prefixes from an area into a summarized inter-area route. This reduces the number of Type 3 Summary LSAs that need to represent individual networks in other areas. Summarization can also reduce routing-table size and limit the propagation of topology changes caused by individual prefixes within the summarized range. A virtual link is used to provide logical backbone connectivity, passive-interface controls OSPF adjacency formation, and router priority influences DR/BDR election on multiaccess networks. Therefore, area range summarization is the appropriate feature for reducing inter-area route advertisements.

Question 283. Two routers are configured as iBGP peers, but a route learned from one iBGP peer is not advertised to another iBGP peer. Which BGP mechanism explains this behavior?

1. iBGP split-horizon rule
2. MED comparison
3. eBGP multihop requirement
4. BGP maximum-prefix protection

Correct Answer: 1. iBGP split-horizon rule

Explanation :-

By default, BGP follows an iBGP split-horizon rule: a route learned from an iBGP peer is not advertised to another iBGP peer. This prevents routing loops within an autonomous system. To distribute iBGP-learned routes without creating a full mesh of iBGP sessions, service-provider networks commonly use route reflectors or BGP confederations. MED is a path-selection attribute, eBGP multihop affects the TTL used for external BGP sessions, and maximum-prefix limits the number of prefixes accepted from a peer. Therefore, the lack of advertisement between two iBGP peers is explained by the iBGP split-horizon rule.

Question 284. A provider has two external connections and wants all internally learned BGP routes to prefer one exit point for outbound traffic. Which BGP attribute should be increased?

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

Correct Answer: 3. LOCAL_PREF

Explanation :-

LOCAL_PREF is used within an autonomous system to influence the preferred outbound path for traffic leaving that AS. A higher LOCAL_PREF value is preferred during BGP best-path selection. Therefore, if a provider wants routers throughout its AS to prefer one external exit point, it can assign a higher LOCAL_PREF to routes associated with that exit. AS_PATH length can influence path selection but is not the normal mechanism for establishing an internal outbound preference across the AS. MED is primarily used to influence how neighboring autonomous systems select an entry point, while ORIGIN has a later role in BGP path selection.

Question 285. A router forwards an MPLS packet through the core and changes the top label to another label before sending it to the next router. Which MPLS operation is being performed?

1. Push
2. Swap
3. Pop
4. Penultimate-hop popping

Correct Answer: 2. Swap

Explanation :-

An MPLS label swap occurs when a router receives a labeled packet and replaces the incoming top label with a different outgoing label before forwarding the packet. This operation is typically performed by an MPLS transit router according to its LFIB. Push adds a label to the packet, while pop removes a label. Penultimate-hop popping is a specific form of label removal normally performed by the router immediately before the egress LSR. Label swapping is therefore the standard operation when a transit MPLS router changes one top label into another.

Question 286. An eBGP session must be established between two routers whose loopback interfaces are several IP hops apart. Which configuration is typically required to allow the BGP session to use those loopback addresses?

1. BGP route dampening
2. BGP community filtering
3. BGP maximum-prefix
4. eBGP multihop

Correct Answer: 4. eBGP multihop

Explanation :-

By default, eBGP uses a low TTL value because external peers are normally directly connected. When eBGP peers use loopback addresses or are separated by multiple routed hops, the default TTL may not be sufficient. The ebgp-multihop feature increases the TTL so the TCP session can traverse the required number of hops. The loopback addresses must also be reachable through the underlying routing system. Route dampening, community filtering, and maximum-prefix are unrelated to the TTL requirement for establishing the multihop eBGP session. Thus, eBGP multihop is the appropriate configuration feature.

Question 287. An OSPF area should not receive external routes from the rest of the OSPF domain, but routers in the area still need connectivity to external destinations. Which area type is appropriate?

1. Backbone area
2. NSSA
3. Stub area
4. Transit area

Correct Answer: 3. Stub area

Explanation :-

An OSPF stub area blocks external Type 5 LSAs from entering the area. Instead, the ABR can provide a default route so routers inside the stub area can reach destinations outside the area without maintaining individual external route information. This can reduce the size of the link-state database and simplify routing in areas where detailed external routes are unnecessary. An NSSA permits certain external routes to be introduced locally using Type 7 LSAs, so it serves a different requirement. The backbone area provides the central inter-area connectivity structure, while a transit area is not the appropriate OSPF area type for this filtering requirement.

Question 288. A BGP policy must add a community to an existing set of communities without removing the communities already attached to the route. Which community action should be used?

1. Additive
2. Replace
3. Delete
4. Clear

Correct Answer: 1. Additive

Explanation :-

The additive community action allows a configured BGP community to be added while preserving the communities already associated with the route. Without the additive behavior, assigning a new community set in some policy configurations can replace the existing community values. Communities are commonly used to communicate routing-policy information between provider routers, customers, or peers. The additive keyword is therefore important when multiple policy signals must coexist on the same route. Replace, delete, and clear do not describe the required behavior of preserving the existing communities while adding another community.

Question 289. A customer VPN route is present in a provider PE router’s BGP VPNv4 table, but it is not imported into the expected customer VRF. What should be checked first?

1. OSPF DR priority
2. LDP router ID
3. BGP Weight
4. Route Target import configuration

Correct Answer: 4. Route Target import configuration

Explanation :-

In an MPLS Layer 3 VPN, Route Targets determine which VPN routes are imported into a VRF. A VPNv4 route can exist in the provider’s MP-BGP table while remaining absent from a particular VRF if its Route Target does not match the VRF’s configured import RT. The Route Distinguisher makes otherwise overlapping prefixes unique in the VPNv4 address space, but it does not determine VRF import membership. LDP router ID and OSPF DR priority are unrelated to this specific import decision. Therefore, the VRF’s Route Target import configuration should be checked first.

Question 290. A service provider requires authentication between IS-IS routers so that unauthorized devices cannot form trusted adjacencies. Which feature addresses this requirement?

1. OSPF area range
2. IS-IS authentication
3. BGP Add-Path
4. MPLS PHP

Correct Answer: 2. IS-IS authentication

Explanation :-

IS-IS authentication allows routers to validate routing protocol messages exchanged with their neighbors. Authentication can be applied according to the supported IS-IS authentication mechanisms and deployment requirements, helping prevent unauthorized or malformed routing information from being accepted. OSPF area range is used for route summarization, BGP Add-Path allows multiple BGP paths to be advertised, and MPLS PHP removes an MPLS label before the egress router. None of those features provides IS-IS neighbor authentication. Therefore, IS-IS authentication is the correct mechanism for securing IS-IS routing exchanges.

Question 291. In a PIM-SM network, which component is responsible for distributing information that allows routers to learn the RP associated with multicast groups?

1. Bootstrap Router (BSR)
2. MPLS LDP router
3. BGP route reflector
4. OSPF DR

Correct Answer: 1. Bootstrap Router (BSR)

Explanation :-

PIM-SM can use the Bootstrap Router mechanism to distribute RP information throughout the PIM domain. Candidate RPs advertise their group mappings, and the BSR distributes the resulting information so PIM routers can determine which RP should be used for relevant multicast groups. The BSR therefore provides a dynamic mechanism for RP discovery and distribution. An OSPF DR handles OSPF multiaccess-network responsibilities, a BGP route reflector distributes BGP routes, and an MPLS LDP router handles label distribution. None of those functions provides PIM-SM RP discovery.

Question 292. A provider uses both a Route Distinguisher and Route Targets for an MPLS Layer 3 VPN. What is the primary purpose of the Route Distinguisher?

1. Select the preferred VPN path
2. Determine multicast RPF
3. Make overlapping customer prefixes unique in VPNv4
4. Control VRF route import

Correct Answer: 3. Make overlapping customer prefixes unique in VPNv4

Explanation :-

The Route Distinguisher (RD) converts potentially overlapping customer IPv4 prefixes into unique VPNv4 routes. For example, identical IPv4 prefixes used by different customers can coexist because their VPNv4 representations contain different RDs. The RD provides uniqueness but does not itself determine which VRFs import the route. Route Targets perform that policy function by controlling route import and export. The RD also does not select the preferred path or determine multicast RPF. Therefore, its primary role is to make overlapping customer prefixes distinguishable within the VPNv4 address family.

Question 293. A BGP route should not be advertised to any other BGP peers after it is received by a router. Which well-known community provides this behavior?

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

Correct Answer: 2. NO_ADVERTISE

Explanation :-

The NO_ADVERTISE well-known BGP community instructs a BGP speaker not to advertise a route to any BGP peer. This provides stronger propagation control than NO_EXPORT, which allows the route to be advertised within the local autonomous system but prevents propagation outside it under the standard community semantics. LOCAL_PREF is used for internal path preference, while ORIGIN is a BGP path attribute used during best-path selection. Therefore, when the requirement is to prevent the route from being advertised to any BGP peer, NO_ADVERTISE is the appropriate community.

Question 294. An OSPF router receives information about networks located in another OSPF area. Which LSA type normally carries these inter-area network prefixes from an ABR?

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

Correct Answer: 4. Type 3

Explanation :-

OSPF Type 3 Summary LSAs are generated by an Area Border Router to advertise networks from one area into another area. They allow routers in an area to learn about inter-area destinations without receiving the complete detailed topology database of every other area. Type 1 Router LSAs describe router links within an area, Type 2 Network LSAs describe multiaccess network segments and are generated by DRs, and Type 5 External LSAs describe routes redistributed from outside the OSPF autonomous system. Therefore, Type 3 LSAs are the normal mechanism for advertising inter-area network prefixes.

Question 295. A BGP session must detect a failed forwarding path much faster than normal BGP keepalive timers allow. Which protocol can provide rapid failure detection and notify BGP?

1. OSPF
2. IS-IS
3. BFD
4. LDP

Correct Answer: 3. BFD

Explanation :-

Bidirectional Forwarding Detection (BFD) provides rapid detection of forwarding-path failures using lightweight control messages and short detection intervals. BGP can be associated with BFD so that a forwarding failure can cause the BGP session or associated route handling to react much faster than relying solely on standard BGP hold timers. OSPF and IS-IS are routing protocols rather than a general-purpose rapid forwarding-failure detection mechanism, while LDP distributes MPLS labels. BFD is therefore the appropriate protocol when the service provider requires fast failure detection for a BGP-controlled path.

Question 296. In Segment Routing over MPLS, an engineer wants to force traffic through a particular link rather than simply toward a destination node. Which SID type is most appropriate?

1. Adjacency SID
2. Node SID
3. Prefix-independent label
4. VPN label

Correct Answer: 1. Adjacency SID

Explanation :-

An Adjacency SID identifies a specific adjacency or link and can be used in a Segment Routing path to explicitly steer traffic over that link. This provides more granular path control than a Node SID, which normally represents reachability toward a particular node. By including an Adjacency SID in a segment list, the ingress node can impose a path that follows a desired link even when the normal shortest path would use another interface. A VPN label serves MPLS VPN forwarding and is not a Segment Routing topology-steering SID. Therefore, an Adjacency SID is appropriate for explicit link-level steering.

Question 297. An OSPF administrator wants to summarize multiple contiguous internal prefixes at an ABR to reduce inter-area routing information. Which command concept should be used?

1. default-information originate
2. passive-interface
3. virtual-link
4. area range

Correct Answer: 4. area range

Explanation :-

The OSPF area range configuration is used on an ABR to summarize multiple prefixes from an area into a broader address range. This reduces the number of individual inter-area routes advertised into other areas and can reduce routing-table complexity. It can also limit the propagation of some topology changes within the summarized address space. default-information originate concerns advertisement of a default route, passive-interface controls adjacency behavior on an interface, and virtual-link provides logical backbone connectivity. Therefore, area range is the appropriate configuration concept for inter-area summarization.

Question 298. An iBGP router learns an external route from an eBGP peer and must advertise that route to an internal BGP peer. The internal peer cannot reach the original external next hop. Which configuration commonly solves this problem?

1. BGP dampening
2. next-hop-self
3. BGP maximum-prefix
4. NO_EXPORT

Correct Answer: 2. next-hop-self

Explanation :-

When an eBGP-learned route is advertised into iBGP, the original BGP next-hop is normally preserved. If internal routers cannot reach that next-hop address, they may receive the route but fail to install or use it effectively. Configuring next-hop-self on the internal BGP speaker changes the next-hop attribute to the advertising router’s own address, provided that router is reachable internally. This makes the route usable without requiring internal routers to have direct reachability to the external next-hop. BGP dampening, maximum-prefix, and NO_EXPORT do not solve next-hop reachability.

Question 299. Two PIM routers on a shared LAN both believe they should forward multicast traffic toward the same receiver segment. Which PIM mechanism elects a single forwarder to prevent duplicate forwarding?

1. PIM Assert
2. PIM BSR
3. IGMP Snooping
4. MSDP

Correct Answer: 1. PIM Assert

Explanation :-

PIM Assert is used when multiple PIM routers on a shared network segment could forward the same multicast traffic. The routers exchange Assert messages and use the defined Assert election rules to determine which router should remain the forwarder for that multicast flow on the interface. The losing router stops forwarding that traffic on the shared segment, helping prevent duplicate multicast packets. BSR distributes RP information, IGMP Snooping operates at the Layer 2 multicast-management level, and MSDP exchanges source information between multicast domains or RPs. Therefore, PIM Assert provides the required forwarder election.

Question 300. A provider wants a BGP speaker to advertise multiple valid paths for the same prefix to another BGP speaker instead of advertising only the selected best path. Which feature provides this capability?

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

Correct Answer: 3. BGP Add-Path

Explanation :-

BGP Add-Path allows a BGP speaker to advertise multiple paths for the same prefix rather than limiting advertisements to a single best path. This can improve path diversity and help downstream routers maintain alternate paths, which can be valuable for traffic engineering and faster convergence. The feature requires compatible Add-Path capabilities and configuration on the participating BGP speakers. Route dampening is used to control unstable routes, conditional advertisement controls route announcements based on policy conditions, and maximum-prefix protects a BGP session from receiving excessive routes. Therefore, BGP Add-Path provides the required multiple-path advertisement capability.