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

 

Question 301. A provider is troubleshooting an IS-IS adjacency that repeatedly fails to reach the Up state. The two routers are configured for different IS-IS levels and cannot establish the required adjacency. Which configuration should be verified first?

1. BGP MED
2. IS-IS level configuration
3. MPLS PHP behavior
4. BGP community attributes

Correct Answer: 2. IS-IS level configuration

Explanation :-

IS-IS routers establish adjacencies according to their configured levels and the capabilities advertised in IS-IS Hello packets. A mismatch between the required Level-1 or Level-2 operation can prevent the intended adjacency from forming. When troubleshooting an adjacency that does not reach the expected state, the engineer should verify the interface-level IS-IS configuration, level compatibility, area addressing where applicable, and authentication. BGP MED and community attributes do not affect IS-IS adjacency formation, while MPLS PHP operates after label-switched forwarding has been established. Therefore, verifying the IS-IS level configuration is an appropriate first step.

Question 302. An OSPF router is configured as an ABR and must prevent selected inter-area prefixes from being advertised into another area. Which mechanism can be used to control the inter-area route advertisements?

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

Correct Answer: 4. OSPF area filtering

Explanation :-

OSPF area filtering can be used on an ABR to control which inter-area routes are advertised between areas. This provides a way to limit the propagation of selected prefixes while maintaining the overall OSPF area structure. The exact filtering mechanism and command syntax depend on the platform and OSPF implementation. DR election and router priority are associated with multiaccess network adjacency roles, while passive-interface prevents adjacency formation on a particular interface. Therefore, when the requirement specifically concerns controlling inter-area route propagation, OSPF area filtering is the relevant mechanism.

Question 303. A service provider has two BGP paths to the same destination. All earlier best-path attributes are equivalent, but one path has a shorter AS_PATH. Which path is normally preferred?

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

Correct Answer: 1. The path with the shorter AS_PATH

Explanation :-

AS_PATH length is one of the attributes considered during BGP best-path selection. When higher-priority attributes such as weight or LOCAL_PREF are equivalent, and the applicable comparison reaches AS_PATH, the path with the shorter AS_PATH is generally preferred. A shorter path does not necessarily represent the physically shortest network path; it represents fewer autonomous-system hops in the BGP path attribute. MED and other attributes can affect selection at different stages, while a lower LOCAL_PREF is generally less preferred than a higher value. Therefore, under the stated conditions, the shorter AS_PATH is selected.

Question 304. An ISP wants to influence inbound traffic from a neighboring autonomous system so that the neighbor prefers a different entry point into the ISP. Which technique can be used to make a particular advertised route appear less attractive by increasing its AS_PATH length?

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

Correct Answer: 3. AS_PATH prepending

Explanation :-

AS_PATH prepending adds additional copies of the ISP’s autonomous-system number to the AS_PATH attribute of selected advertisements. A neighboring AS may then consider that path less attractive because it has a longer AS_PATH compared with another available path, assuming relevant earlier attributes do not override the comparison. This technique is commonly used for influencing inbound traffic engineering. LOCAL_PREF primarily influences outbound path selection inside an AS, BGP Weight is Cisco-specific and local to a router, and BFD provides fast failure detection. Therefore, AS_PATH prepending is the appropriate technique for the described inbound traffic-engineering goal.

Question 305. A PE router receives a customer route through MP-BGP but the route does not appear in the expected VRF routing table. The route carries an RT that does not match the VRF’s import policy. What is the likely result?

1. The route is automatically imported because the RD matches
2. The route becomes an OSPF external route
3. The route is converted into a global IPv4 route
4. The route is not imported into that VRF

Correct Answer: 4. The route is not imported into that VRF

Explanation :-

Route Targets control VPN route import and export policy in an MPLS Layer 3 VPN. When a VPN route is received through MP-BGP, the PE examines its extended community attributes, including Route Targets. If none of the route’s RTs match the import RT configured for a VRF, the route is not imported into that VRF. The Route Distinguisher provides uniqueness for VPN routes but does not determine VRF import policy. The route therefore can remain present in the VPNv4 BGP table while being absent from the specific customer VRF. This behavior is an important MPLS L3VPN troubleshooting point.

Question 306. An MPLS router receives a packet with label 200 and its LFIB specifies label 200 should be replaced with label 350 before forwarding. What operation occurs?

1. Pop
2. Label swap
3. Push
4. PHP

Correct Answer: 2. Label swap

Explanation :-

MPLS label swapping occurs when an LSR replaces the incoming top label with another outgoing label according to its LFIB. In this example, label 200 is replaced by label 350, so the operation is a label swap. A push operation adds a label to the existing stack, while a pop removes the top label. Penultimate-hop popping is a specific label-removal operation performed by the router immediately before the egress LSR in many MPLS forwarding scenarios. Therefore, replacing label 200 with label 350 is directly described as an MPLS label swap.

Question 307. A service provider wants to protect a BGP session against forwarding failures with detection intervals significantly shorter than typical BGP hold timers. Which protocol is designed for this purpose?

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

Correct Answer: 3. BFD

Explanation :-

Bidirectional Forwarding Detection is designed to provide rapid detection of forwarding-path failures. BFD uses lightweight control messages and can operate with short detection intervals, allowing protocols such as BGP to react much faster than they would using their normal keepalive and hold timers alone. RSVP-TE is used for traffic-engineered MPLS paths, LDP distributes labels, and MSDP exchanges multicast source information between domains or rendezvous points. Therefore, BFD is the appropriate protocol when rapid forwarding-failure detection is required for a BGP session.

Question 308. In an OSPF NSSA, a router redistributes an external route into the area. Which LSA type is initially used to represent that external route within the NSSA?

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

Correct Answer: 1. Type 7

Explanation :-

OSPF Not-So-Stubby Areas allow external routes to be introduced into an otherwise stub-like area. External routes redistributed into an NSSA are represented using Type 7 LSAs. An NSSA ABR can translate eligible Type 7 information into Type 5 external LSAs for advertisement into the rest of the OSPF domain. Type 3 LSAs represent inter-area networks, Type 2 LSAs describe transit multiaccess networks, and Type 5 LSAs normally represent external routes outside an NSSA. Therefore, Type 7 is the correct LSA type initially used within the NSSA.

Question 309. A BGP route reflector receives a route from one client and needs to advertise it to another route-reflector client. Which behavior allows this without requiring a full iBGP mesh?

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

Correct Answer: 2. Route reflection

Explanation :-

BGP route reflection provides a scalable alternative to a full mesh of iBGP sessions. A route reflector can accept routes from its clients and reflect those routes to other clients according to the route-reflection rules. This allows groups of iBGP routers to exchange routing information without every router maintaining a direct session with every other iBGP router. The route reflector also uses attributes such as ORIGINATOR_ID and CLUSTER_LIST to help prevent routing loops. MED, AS_PATH prepending, and dampening are unrelated to the basic mechanism of reflecting client-learned routes.

Question 310. A provider wants to advertise only a default route to a customer over BGP and prevent the customer’s receipt of the provider’s full routing table. Which policy approach is appropriate?

1. Advertise all routes and increase MED
2. Use AS_PATH prepending only
3. Enable BGP Add-Path
4. Apply a prefix filter or routing policy that permits only 0.0.0.0/0

Correct Answer: 4. Apply a prefix filter or routing policy that permits only 0.0.0.0/0

Explanation :-

A prefix filter or routing policy can explicitly permit only the default route, 0.0.0.0/0, for advertisement to the customer. This prevents other provider prefixes from being exported over the customer BGP session. The policy should be applied in the appropriate direction and verified with BGP route-policy or prefix-list inspection commands. AS_PATH prepending changes path preference rather than restricting which prefixes are advertised. Add-Path provides multiple path advertisements and does not perform this filtering function. Therefore, permitting only the default prefix through policy is the correct approach.

Question 311. An IS-IS Level-1 router needs to reach a destination outside its local area. What route is commonly used to provide connectivity toward the Level-2 portion of the IS-IS domain?

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

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

Explanation :-

An IS-IS Level-1 router maintains knowledge of destinations within its local area but does not maintain the complete Level-2 topology. Level-1-2 routers can provide connectivity from the Level-1 area toward the Level-2 backbone. A Level-1 router commonly uses a default route toward a suitable Level-1-2 router for destinations outside the local area. BGP MED, MPLS VPN labels, and OSPF Type 5 LSAs do not provide the normal IS-IS Level-1-to-Level-2 forwarding mechanism. Therefore, a default route toward a Level-1-2 router is the expected solution.

Question 312. A BGP speaker must prevent a route from being advertised outside its local autonomous system while still allowing it to be advertised to other routers inside that autonomous system. Which community should be applied?

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

Correct Answer: 1. NO_EXPORT

Explanation :-

The NO_EXPORT well-known BGP community indicates that a route should not be advertised outside the local autonomous system or confederation boundary according to the applicable BGP semantics. This allows the route to continue being distributed within the local AS while restricting external propagation. NO_ADVERTISE is more restrictive because it prevents advertisement to any BGP peer. The additive keyword controls how communities are appended and does not itself define a propagation boundary. Therefore, NO_EXPORT is the appropriate community when internal propagation is permitted but external advertisement should be prevented.

Question 313. A provider uses Segment Routing and wants to represent a specific router as a segment that can be included in a segment list. Which SID normally represents the node’s shortest-path reachability?

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

Correct Answer: 4. Node SID

Explanation :-

A Segment Routing Node SID represents a node and normally corresponds to shortest-path forwarding toward that node according to the IGP topology. When included in a segment list, the Node SID can direct traffic toward the associated router without explicitly identifying every intermediate link. An Adjacency SID is used to identify a particular adjacency, while a Binding SID represents an SR Policy or segment-list construct. A VPN label belongs to MPLS VPN forwarding rather than identifying a Segment Routing node. Therefore, the Node SID is the appropriate SID for representing a router’s reachability.

Question 314. A BGP route reflector receives the same route from multiple clients. Which attribute helps identify the route’s originating client and assists in preventing reflection loops?

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

Correct Answer: 2. ORIGINATOR_ID

Explanation :-

ORIGINATOR_ID is a BGP attribute used by route reflectors to identify the originator of a reflected route. When a route reflector reflects a route learned from a client, it can add the ORIGINATOR_ID associated with the originating router. This information helps prevent routing loops and allows route reflectors to recognize routes that originated from a particular client. CLUSTER_LIST provides another loop-prevention mechanism by recording route-reflector cluster information. MED, LOCAL_PREF, and Cisco Weight serve path-selection purposes rather than identifying the original route-reflector client.

Question 315. An MPLS network has a label stack where the outer transport label is removed by the router immediately before the egress LSR. Which operation is this?

1. Penultimate-hop popping
2. Label push
3. Label swap
4. VPN label imposition

Correct Answer: 1. Penultimate-hop popping

Explanation :-

Penultimate-hop popping, commonly abbreviated PHP, removes the top MPLS label at the penultimate router before the packet reaches the egress LSR. This allows the egress router to process the packet without having to perform the final transport-label lookup. PHP is commonly associated with an implicit-null label advertisement from the egress LSR. A label push adds a label, a swap replaces a label, and VPN label imposition adds a service-specific label when entering an MPLS VPN forwarding path. Therefore, removal of the outer transport label by the penultimate router is PHP.

Question 316. A multicast receiver joins a group using source-specific multicast and specifies both the multicast group and the desired source. Which membership protocol version is commonly required for this information?

1. IGMPv1
2. IGMPv2
3. IGMPv3
4. IGMPv1 with PIM Register

Correct Answer: 3. IGMPv3

Explanation :-

Source-Specific Multicast requires receivers to identify both the multicast group and the specific source from which they want traffic. IGMPv3 supports source filtering and therefore provides the membership information needed for IPv4 SSM operation. Earlier IGMP versions do not provide the same source-specific membership capability. PIM-SM and its RP-based mechanisms are associated with traditional ASM operation, while SSM can use source-specific joins without requiring the same shared-tree process. Therefore, IGMPv3 is the protocol version normally used when an IPv4 receiver must explicitly specify its desired multicast source.

Question 317. A provider wants to advertise multiple BGP paths for the same prefix so downstream routers can retain path diversity instead of receiving only the single best path. Which feature should be enabled?

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

Correct Answer: 2. BGP Add-Path

Explanation :-

BGP Add-Path extends normal BGP behavior so a speaker can advertise multiple paths for the same prefix. This can provide additional path diversity to downstream routers and may improve convergence or traffic-engineering options in suitable deployments. Standard BGP normally advertises only the selected best path for a given prefix to a peer. Route dampening is intended to reduce the impact of route instability, conditional advertisement controls announcements based on conditions, and maximum-prefix provides protection against receiving excessive routes. Therefore, BGP Add-Path is the appropriate feature for advertising multiple valid paths.

Question 318. A PE router exports customer VPN routes to MP-BGP. Which attribute determines the VPN import policy used by remote VRFs?

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

Correct Answer: 4. Route Target

Explanation :-

Route Targets are extended BGP communities used to control MPLS VPN route import and export policies. When a PE exports a customer route, it attaches one or more export Route Targets. A remote PE imports that VPN route into a VRF when the route’s Route Target matches an import Route Target configured for that VRF. The Route Distinguisher has a different purpose: it makes overlapping customer prefixes unique in the VPNv4 or VPNv6 address space. LOCAL_PREF and Weight are path-selection attributes. Therefore, Route Target is the attribute that controls VPN import policy.

Question 319. An engineer observes a PIM multicast route in (S,G) state, but traffic from the source is being discarded because the incoming interface is not the expected interface toward the source. Which multicast mechanism determines whether the incoming path is valid?

1. BSR
2. MSDP
3. Reverse Path Forwarding
4. IGMP Snooping

Correct Answer: 3. Reverse Path Forwarding

Explanation :-

PIM routers use Reverse Path Forwarding checks to verify that multicast packets arrive on the interface the unicast routing table considers the correct path toward the source. If packets arrive on an unexpected interface, the RPF check can fail and the router may discard the multicast traffic. This protects against forwarding loops and incorrect multicast forwarding paths. BSR distributes RP information, MSDP exchanges source information between multicast domains or RPs, and IGMP Snooping operates at the Layer 2 switching level. Therefore, RPF is the mechanism that validates the expected incoming multicast path.

Question 320. A BGP administrator wants a route to be advertised only when another specified route is present in the BGP routing table. Which BGP feature directly supports this conditional behavior?

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

Correct Answer: 1. BGP conditional advertisement

Explanation :-

BGP conditional advertisement allows a router to advertise selected routes based on the presence or absence of another route or condition in the routing information. This can be useful for backup connectivity and controlled route advertisement scenarios. The policy can be designed so that a route is advertised only when a specified condition is satisfied. BGP Add-Path controls the advertisement of multiple paths, maximum-prefix protects a session from excessive route reception, and route dampening helps suppress unstable routes. Therefore, conditional advertisement is the feature specifically designed for making BGP route announcements dependent on another routing condition.