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

 

Question 361. An IS-IS Level-1 router has an adjacency with a Level-1-2 router but cannot reach a destination outside its local area. Which routing information should the Level-1 router normally use?

1. A Type 5 LSA
2. A BGP community
3. A default route toward the Level-1-2 router
4. An MPLS VPN label

Correct Answer: 3. A default route toward the Level-1-2 router

Explanation :-

IS-IS Level-1 routers focus on routing within their local area and do not maintain the complete Level-2 topology. A Level-1-2 router provides connectivity between the local Level-1 area and the Level-2 backbone. The Level-1 router can therefore use a default route pointing toward a suitable Level-1-2 router for destinations outside its area. OSPF Type 5 LSAs, BGP communities, and MPLS VPN labels are not the normal mechanism for Level-1 inter-area forwarding. When troubleshooting this situation, the engineer should verify the Level-1 routing table and the presence and reachability of the appropriate default route.

Question 362. An OSPF ABR must prevent selected inter-area prefixes from being advertised into a neighboring area. Which mechanism is designed for controlling inter-area route propagation?

1. OSPF area filtering
2. OSPF router priority
3. OSPF passive interface
4. OSPF DR election

Correct Answer: 1. OSPF area filtering

Explanation :-

OSPF area filtering can be used on an ABR to control which inter-area routes are advertised between areas. This is useful when a provider needs to limit the propagation of selected prefixes while preserving normal OSPF connectivity for permitted routes. Router priority and DR election concern the selection of designated routers on multiaccess networks, while passive-interface controls whether an interface forms OSPF adjacencies. These mechanisms do not provide selective inter-area route filtering. Therefore, when the requirement specifically involves controlling which inter-area prefixes are advertised into another area, OSPF area filtering is the appropriate mechanism.

Question 363. Two BGP paths to the same destination have different LOCAL_PREF values. All other relevant attributes are equal. Which path is preferred?

1. The path with the lower LOCAL_PREF
2. The path with the longer AS_PATH
3. The path with the lower MED
4. The path with the higher LOCAL_PREF

Correct Answer: 4. The path with the higher LOCAL_PREF

Explanation :-

LOCAL_PREF is a major BGP attribute used to influence outbound path selection within an autonomous system. When comparing otherwise eligible routes, a higher LOCAL_PREF is preferred over a lower value. This allows an ISP to establish a consistent preferred exit point across its network. AS_PATH length, MED, and other attributes are considered at different stages of the BGP best-path process. Therefore, if LOCAL_PREF is the differentiating attribute and all higher-priority considerations are equal, the route carrying the higher LOCAL_PREF value is selected.

Question 364. An ISP wants to make one advertised route less attractive to an external neighbor without changing the neighbor’s internal LOCAL_PREF. Which technique can increase the apparent path length?

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

Correct Answer: 2. AS_PATH prepending

Explanation :-

AS_PATH prepending adds additional copies of an autonomous-system number to the AS_PATH attribute of an advertised route. This makes the path appear longer to the receiving autonomous system and can cause that neighbor to prefer an alternative path when relevant earlier attributes are equal. This technique is commonly used for inbound traffic engineering. Weight is local to the router and does not propagate to the neighbor, while LOCAL_PREF is normally controlled inside the receiving AS. BFD provides fast failure detection rather than changing BGP path preference. Therefore, AS_PATH prepending is appropriate for this requirement.

Question 365. A PE router receives a VPNv4 route containing an RD that matches the expected customer context, but the route is not imported into the target VRF. Which value should be checked next?

1. Route Target
2. BGP Weight
3. MED
4. OSPF router priority

Correct Answer: 1. Route Target

Explanation :-

The Route Distinguisher and Route Target perform different functions in MPLS L3VPNs. The RD makes overlapping customer prefixes unique within VPNv4, while Route Targets control import and export policy. If a VPNv4 route is present in MP-BGP but is absent from the expected VRF, the engineer should verify whether the route’s Route Target matches an import RT configured under that VRF. Weight and MED influence BGP path selection, and OSPF router priority is unrelated to VPN route import. Therefore, the Route Target should be checked next.

Question 366. A BGP router is receiving a large number of customer routes and the operator wants to protect the router if the number of received prefixes exceeds a predefined threshold. Which feature should be configured?

1. BGP Add-Path
2. Route reflection
3. Maximum-prefix
4. Conditional advertisement

Correct Answer: 3. Maximum-prefix

Explanation :-

BGP maximum-prefix protection limits the number of prefixes that a router will accept from a BGP neighbor. This is particularly useful on customer and peer sessions where an accidental route leak or configuration error could cause an unexpectedly large number of routes to be received. When the configured threshold is exceeded, the router can take protective action according to the implementation and configured options. Add-Path provides multiple path advertisements, route reflection improves iBGP scalability, and conditional advertisement controls route announcements based on routing conditions. Therefore, maximum-prefix is the appropriate protection mechanism.

Question 367. An OSPF router on a broadcast network is a DROTHER and has established a 2-Way relationship with another DROTHER. Is this state necessarily a problem?

1. Yes, all routers must reach Full state with every neighbor
2. No, DROTHER routers normally remain at 2-Way with each other
3. Yes, the routers must become BDRs
4. No, because OSPF does not form adjacencies on broadcast networks

Correct Answer: 2. No, DROTHER routers normally remain at 2-Way with each other

Explanation :-

On an OSPF broadcast multiaccess network, routers elect a Designated Router and Backup Designated Router. DROTHER routers generally form full adjacencies with the DR and BDR, while their relationships with other DROTHER routers normally remain in the 2-Way state. This reduces the number of full adjacencies required on the shared segment. Therefore, seeing 2-Way between two DROTHER routers is expected behavior rather than an indication of an adjacency failure. The DR and BDR provide the central adjacency relationships needed for efficient OSPF database synchronization on the broadcast network.

Question 368. A provider needs to make a specific link mandatory in a Segment Routing path. Which SID provides explicit adjacency-level steering?

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

Correct Answer: 4. Adjacency SID

Explanation :-

An Adjacency SID identifies a specific adjacency or link in a Segment Routing topology. By including the appropriate Adjacency SID in a segment list, an operator can explicitly steer traffic through that link instead of relying solely on shortest-path forwarding toward a destination node. A Node SID generally identifies a node and follows the applicable shortest-path behavior, while a Binding SID represents an SR Policy or segment-list construct. A VPN label is associated with MPLS VPN forwarding. Therefore, an Adjacency SID is the appropriate choice for explicit link-level steering.

Question 369. An IS-IS router’s database contains an older version of an LSP, while a neighboring router advertises a newer sequence number for that same LSP. What action should occur?

1. The older LSP should remain preferred
2. The adjacency should be removed
3. The newer LSP should replace the older information
4. The router should ignore the sequence number

Correct Answer: 3. The newer LSP should replace the older information

Explanation :-

IS-IS uses LSP sequence numbers to identify newer and older versions of link-state information. A higher sequence number represents a newer version. When a router receives a newer LSP than the one stored locally, it updates its database with the newer information and participates in flooding that information to maintain synchronization throughout the routing domain. The router does not prefer the older copy or remove the adjacency simply because the database changed. Sequence-number comparison is fundamental to maintaining a consistent IS-IS link-state database.

Question 370. A service provider wants to advertise a customer prefix only when a primary route disappears. Which BGP mechanism can conditionally advertise the backup prefix?

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

Correct Answer: 1. BGP conditional advertisement

Explanation :-

BGP conditional advertisement allows an operator to make the advertisement of a route dependent on the presence or absence of another route or routing condition. A common application is backup connectivity, where a secondary prefix or path should be advertised only when the primary route is unavailable. Add-Path provides multiple path advertisements, maximum-prefix protects against excessive route reception, and route reflection solves iBGP scalability issues. Therefore, conditional advertisement directly addresses the requirement to advertise a backup route when a primary route disappears.

Question 371. A multicast router receives traffic for (S,G) but the packet arrives on an interface that is not the unicast reverse path toward source S. What will normally happen?

1. The router changes the RP automatically
2. The router creates a new BGP path
3. The router converts the route into (*,G)
4. The RPF check can fail and the packet can be discarded

Correct Answer: 4. The RPF check can fail and the packet can be discarded

Explanation :-

PIM multicast forwarding relies on Reverse Path Forwarding checks to prevent loops and validate the source-facing interface. For (S,G) traffic, the router examines its unicast routing information toward source S and expects multicast packets to arrive through the corresponding RPF interface. If the packet arrives through another interface, the RPF check fails and the router can discard the packet. This behavior does not automatically change the RP or create a BGP path. Therefore, an incorrect incoming interface can cause the multicast packet to be dropped because of RPF failure.

Question 372. A BGP route carries a community that should be preserved while another community is added by a routing policy. Which policy behavior should be used?

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

Correct Answer: 2. Additive

Explanation :-

The additive behavior allows a new BGP community to be added without removing the communities that are already associated with the route. This is useful when multiple policy signals must remain attached to a route as it passes through different provider routers. Without appropriate additive behavior, a policy that assigns a new community set can potentially replace the existing set depending on the implementation and configuration. Replace, clear, and strip do not provide the required preservation-and-add behavior. Therefore, the additive community action is appropriate when the existing communities must remain intact.

Question 373. An OSPF router must advertise a default route into an area only when a specified external condition or route exists. Which OSPF feature can support conditional default origination?

1. Conditional default-information originate
2. Router priority
3. OSPF passive interface
4. Area range

Correct Answer: 1. Conditional default-information originate

Explanation :-

OSPF can conditionally originate a default route based on the presence of a specified route or condition. This allows a router to advertise 0.0.0.0/0 only when the required external connectivity or routing condition is available. Such behavior is useful when the default route should represent actual upstream reachability rather than always being advertised. Router priority controls DR/BDR election, passive-interface controls adjacency behavior, and area range summarizes prefixes. Therefore, conditional default-information origination is the appropriate feature when default-route advertisement must depend on another routing condition.

Question 374. An MPLS L3VPN packet enters a PE router and must carry information identifying the customer VRF through the provider MPLS network. Which label is associated with the VPN service forwarding context?

1. Transport label only
2. IGP label
3. VPN label
4. BGP community label

Correct Answer: 3. VPN label

Explanation :-

In an MPLS Layer 3 VPN, the VPN label identifies the appropriate VPN forwarding context at the egress PE. The transport label is used to carry the packet across the MPLS core toward the egress PE, while the VPN label allows the egress router to determine the appropriate VRF or service forwarding context. BGP communities such as Route Targets provide control-plane policy information rather than serving as MPLS data-plane labels. Therefore, the VPN label is the label associated with the customer VPN forwarding context.

Question 375. A provider uses PIM-SM and wants multicast routers to dynamically learn which RP should be used for particular multicast groups. Which mechanism should be deployed?

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

Correct Answer: 4. PIM BSR

Explanation :-

PIM Bootstrap Router (BSR) functionality provides a dynamic method for distributing Rendezvous Point information in a PIM-SM domain. Candidate RPs can advertise their services, and the BSR distributes RP information so routers can determine the appropriate RP for multicast groups. IGMP Snooping operates within Layer 2 switches, BFD detects forwarding failures, and MSDP exchanges multicast source information between appropriate multicast domains or RPs. Therefore, PIM BSR is the mechanism used for dynamic RP information distribution within the PIM-SM domain.

Question 376. A BGP administrator wants to advertise only approved customer prefixes to an upstream provider. Which policy should be applied in the outbound direction?

1. An MPLS VPN label policy
2. A prefix-list-based routing policy
3. An IS-IS authentication policy
4. A PIM RPF policy

Correct Answer: 2. A prefix-list-based routing policy

Explanation :-

An outbound BGP routing policy can reference a prefix list that explicitly identifies which customer prefixes are permitted for advertisement to the upstream provider. This is a standard method of preventing accidental route leaks and ensuring that only authorized networks are announced. The policy can also include additional conditions or modifications as required. MPLS VPN labels are data-plane forwarding information, IS-IS authentication secures IS-IS exchanges, and PIM RPF controls multicast forwarding validation. Therefore, a prefix-list-based routing policy applied outbound is appropriate for controlling customer prefix advertisements.

Question 377. A Segment Routing deployment uses a Node SID for a destination router. What forwarding behavior does a Node SID normally represent?

1. Forwarding to the specified node using the IGP shortest path
2. Forwarding only through one explicitly selected interface
3. Selection of an MPLS VPN VRF
4. PIM RP selection

Correct Answer: 1. Forwarding to the specified node using the IGP shortest path

Explanation :-

A Segment Routing Node SID identifies a node and normally represents forwarding toward that node along the IGP shortest path. This allows an ingress router to direct traffic toward a specific router without encoding every intermediate hop in the segment list. If the requirement is to force traffic over a particular adjacency, an Adjacency SID provides more granular control. Node SIDs are not used to select MPLS VPN VRFs or PIM RPs. Therefore, the normal behavior of a Node SID is to provide shortest-path forwarding toward the identified node according to the Segment Routing IGP topology.

Question 378. A BGP route reflector receives a route that contains its own cluster ID in the CLUSTER_LIST. What should the route reflector normally do?

1. Accept and reflect the route again
2. Increase LOCAL_PREF
3. Add another copy of its cluster ID and reflect it
4. Reject the route to prevent a reflection loop

Correct Answer: 4. Reject the route to prevent a reflection loop

Explanation :-

The CLUSTER_LIST attribute helps route reflectors detect and prevent routing loops. When a route reflector receives a reflected route containing its own cluster ID in the CLUSTER_LIST, it recognizes that the route has already passed through its cluster. The router should therefore reject the route rather than reflect it again. This mechanism prevents routes from circulating repeatedly between route-reflector clusters. LOCAL_PREF and other BGP path attributes do not replace the loop-prevention function of CLUSTER_LIST. Thus, rejecting the route is the expected behavior when the router detects its own cluster ID.

Question 379. A provider wants to detect a failure between two BGP routers without waiting for the normal BGP hold timer. Which protocol can be integrated with BGP for rapid detection?

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

Correct Answer: 3. BFD

Explanation :-

BFD is designed for rapid detection of forwarding-path failures and can be integrated with BGP. Instead of waiting for standard BGP keepalive and hold timers to expire, BFD can detect loss of connectivity using its own short detection intervals. Once a failure is detected, the associated routing protocol can respond according to the configured integration. LDP distributes labels, RSVP-TE supports MPLS traffic engineering, and MSDP distributes multicast source information. Therefore, BFD is the appropriate protocol for fast BGP failure detection.

Question 380. A service provider wants several valid BGP paths for the same prefix to be advertised to a downstream router instead of only the selected best path. Which feature provides this capability?

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

Correct Answer: 4. BGP Add-Path

Explanation :-

BGP Add-Path allows a BGP speaker to advertise multiple paths for the same network prefix. Standard BGP behavior generally advertises only the selected best path to a peer, while Add-Path can provide additional path diversity to downstream routers. This can support improved convergence and traffic-engineering designs when multiple alternatives are useful. Conditional advertisement controls route announcements based on conditions, maximum-prefix limits received prefixes, and route dampening helps reduce the impact of unstable routes. Therefore, BGP Add-Path is the feature designed to advertise multiple valid paths for the same prefix.