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

 

Question 21. An OSPF neighbor remains stuck in the EXSTART state after the adjacency begins forming. Which issue is a common cause?

1. Incorrect BGP local preference
2. MTU mismatch
3. Missing PIM RP
4. Incorrect MPLS VPN label

Correct Answer: 2. MTU mismatch

Explanation :-

An OSPF adjacency can become stuck in the EXSTART or EXCHANGE state when neighboring interfaces have incompatible MTU values. During database description exchange, an MTU mismatch can prevent the routers from successfully negotiating and processing the expected packets. Administrators should compare the interface MTU values on both ends and inspect OSPF neighbor state transitions. BGP Local Preference, PIM RP configuration, and MPLS VPN labels do not directly determine whether an OSPF adjacency reaches the Full state. MTU mismatches are therefore an important first consideration when an OSPF neighbor repeatedly remains in EXSTART or EXCHANGE.

Question 22. Which IS-IS feature allows a Level-1 router to reach destinations outside its local area without maintaining the complete Level-2 topology?

1. DIS election
2. CSNP flooding
3. LSP fragmentation
4. Level-1 default route toward a Level-2 router

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

Explanation :-

IS-IS Level-1 routers primarily maintain information about their local area. For destinations outside that area, they can use a default route pointing toward an appropriate Level-1-2 router that provides access to the Level-2 backbone. This hierarchical behavior limits the amount of inter-area topology information that must be maintained by Level-1 routers. DIS election is associated with broadcast LAN operation, while CSNPs synchronize link-state databases. LSP fragmentation deals with the handling of large link-state information. The Level-1 default route therefore provides an efficient mechanism for reaching destinations outside the local area.

Question 23. A BGP administrator wants to attach a community to a route while preserving all communities already present. Which keyword is appropriate?

1. Additive
2. Replace
3. Override
4. Remove

Correct Answer: 1. Additive

Explanation :-

The additive behavior allows a newly configured BGP community to be added to the existing community list rather than replacing previously assigned communities. This is useful when multiple policies need to mark a route with different communities for downstream filtering or traffic engineering. Without additive behavior, platform-specific community configuration may replace the existing community set. Community attributes are commonly used in service-provider networks to classify customer routes, control propagation, or influence downstream routing policies. Administrators should therefore understand whether a policy is adding communities or replacing the existing set when implementing BGP route policies.

Question 24. Which BGP mechanism reduces the need for a full mesh of iBGP sessions in a large service-provider network?

1. MED
2. BGP maximum-prefix
3. Route reflection
4. TTL Security

Correct Answer: 3. Route reflection

Explanation :-

BGP route reflection allows a service provider to scale iBGP without requiring every router to establish a direct session with every other iBGP router. Route reflectors receive routes from clients and can reflect appropriate routes to other clients. This significantly reduces the number of required BGP sessions in large networks. Route reflectors also use attributes such as ORIGINATOR_ID and CLUSTER_LIST to help prevent routing loops. MED influences path selection, maximum-prefix limits the number of received routes, and TTL Security protects eBGP sessions. Route reflection is therefore a fundamental iBGP scalability mechanism.

Question 25. A provider wants traffic entering its network through one customer-facing link to be less preferred by the remote AS. Which technique can make that route appear longer?

1. Increasing Local Preference
2. Reducing MED
3. Changing the BGP router ID
4. AS_PATH prepending

Correct Answer: 4. AS_PATH prepending

Explanation :-

AS_PATH prepending adds additional instances of an autonomous-system number to the AS_PATH when advertising a route. A neighboring AS generally prefers a shorter AS_PATH over a longer one when the relevant earlier attributes are equivalent. By prepending the AS number on one advertisement, a provider can make that path less attractive and potentially influence inbound traffic toward another entry point. Local Preference controls outbound path selection within an AS, while MED can influence a neighboring AS’s entry-point selection under applicable comparison rules. AS_PATH prepending is therefore a common inbound traffic-engineering technique.

Question 26. Which MPLS control-plane protocol is commonly used to establish label bindings that follow the IGP shortest path rather than an explicitly engineered path?

1. RSVP-TE
2. LDP
3. BGP
4. PIM

Correct Answer: 2. LDP

Explanation :-

LDP distributes labels for forwarding equivalence classes using the underlying IGP’s reachability information. As a result, the resulting label-switched paths normally follow the paths selected by the IGP. RSVP-TE can establish explicitly engineered MPLS traffic-engineering tunnels, while BGP is used for IP and VPN route distribution and PIM handles multicast routing. LDP therefore provides a straightforward label-distribution mechanism for conventional MPLS forwarding. When troubleshooting an LDP LSP, engineers should verify IGP reachability, LDP discovery, LDP sessions, and label bindings.

Question 27. Which Segment Routing SID is used to force traffic over a specific link between two adjacent routers?

1. Node SID
2. Prefix SID
3. Adjacency SID
4. Binding SID

Correct Answer: 3. Adjacency SID

Explanation :-

An Adjacency SID represents a specific adjacency from one Segment Routing node to another. Using an Adjacency SID allows an SR policy to steer traffic over a particular link instead of relying solely on the destination node’s shortest path. Node or Prefix SIDs generally identify reachability toward a node or prefix, while a Binding SID represents an SR Policy or another segment-routing construct. Adjacency SIDs are particularly valuable for traffic engineering because they provide explicit control over selected links. They can be combined with other SIDs to construct detailed engineered paths through the service-provider topology.

Question 28. In an MPLS L3VPN, which attribute allows identical customer prefixes to remain unique in the provider’s VPN routing table?

1. Route Distinguisher
2. Route Target
3. Local Preference
4. MPLS TTL

Correct Answer: 1. Route Distinguisher

Explanation :-

A Route Distinguisher (RD) makes otherwise identical customer prefixes unique within the VPNv4 or VPNv6 address space. For example, two different customers may both use 10.10.10.0/24, but different RDs allow their routes to be represented as separate VPN routes. The RD provides uniqueness and is not itself the mechanism that determines route import into a VRF. Route Targets control VPN route import and export. Local Preference affects BGP path selection, while MPLS TTL is associated with packet forwarding. Distinguishing RD from RT is essential for understanding MPLS L3VPN operation.

Question 29. Which BGP attribute identifies the IP address that should be used as the next hop toward a destination prefix?

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

Correct Answer: 4. NEXT_HOP

Explanation :-

The BGP NEXT_HOP attribute identifies the IP address that a router should use as the next hop when forwarding traffic toward the advertised prefix. The receiving router must have reachability to that next-hop address for the BGP route to become usable. In iBGP designs, the next-hop-self feature is often used to make an internal router the next hop for routes learned from external peers. ORIGIN describes how the route entered BGP, AS_PATH records autonomous-system traversal, and LOCAL_PREF influences outbound path selection. NEXT_HOP is therefore directly associated with forwarding reachability.

Question 30. Which OSPF area type prevents normal Type 5 external LSAs from entering the area while providing a default route for external reachability?

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

Correct Answer: 2. Stub area

Explanation :-

An OSPF stub area blocks normal Type 5 external LSAs from entering the area and relies on a default route to provide reachability toward destinations outside the OSPF autonomous system. This reduces the amount of external routing information maintained by routers inside the area. An NSSA provides a different behavior because it permits an ASBR within the area to originate external routes using Type 7 LSAs. The backbone area is Area 0 and carries inter-area routing, while a transit area can provide connectivity for specific OSPF designs. Stub areas are therefore useful when detailed external routes are unnecessary.

Question 31. A BGP route is received from an external peer, but the provider wants to advertise it to internal routers without changing the original AS_PATH. Which protocol relationship is normally used?

1. iBGP
2. PIM-SM
3. LDP
4. IS-IS Level 1

Correct Answer: 1. iBGP

Explanation :-

An external BGP route learned by an edge router can be distributed to other routers within the same autonomous system using iBGP. The route’s AS_PATH is generally preserved when the route is propagated internally because the routers belong to the same AS. However, the NEXT_HOP attribute must remain reachable, or the receiving router can use next-hop-self where appropriate. LDP distributes MPLS labels, PIM handles multicast routing, and IS-IS Level 1 is an IGP function. iBGP therefore provides the standard mechanism for distributing external BGP routes within the provider’s autonomous system.

Question 32. Which BGP community is more restrictive than NO_EXPORT because it prevents a route from being advertised to any BGP peer?

1. INTERNET
2. NO_EXPORT
3. NO_ADVERTISE
4. LOCAL_AS

Correct Answer: 3. NO_ADVERTISE

Explanation :-

The NO_ADVERTISE well-known community instructs a BGP speaker not to advertise the route to any BGP peer. This is more restrictive than NO_EXPORT, which permits internal propagation within the autonomous system but prevents advertisement outside it. The INTERNET community indicates normal advertisement behavior, while LOCAL_AS is not the standard well-known community used for this purpose. These communities provide a simple way to communicate route-propagation policies between BGP speakers. Correct application of community-based filtering is especially important in provider networks to prevent accidental route propagation or unwanted transit behavior.

Question 33. Which MPLS table contains the label bindings learned from label-distribution protocols before they are used to build forwarding entries?

1. LIB
2. ARP table
3. RIB
4. MAC address table

Correct Answer: 1. LIB

Explanation :-

The Label Information Base (LIB) contains label bindings learned through MPLS control-plane protocols such as LDP. The router uses these control-plane bindings to determine the appropriate labels associated with forwarding equivalence classes and then installs the necessary information into the forwarding plane, including the LFIB. The RIB contains IP routing information, while ARP and MAC tables provide Layer 2 resolution information. Understanding the difference between the LIB and LFIB is important during MPLS troubleshooting: the LIB represents learned label information, whereas the LFIB represents the forwarding actions actually used for MPLS packets.

Question 34. What is the primary purpose of the MPLS transport label in an MPLS L3VPN packet?

1. To identify the customer’s VRF
2. To identify the BGP community
3. To select the Route Distinguisher
4. To carry the packet toward the appropriate egress PE

Correct Answer: 4. To carry the packet toward the appropriate egress PE

Explanation :-

The outer MPLS transport label is used to forward an MPLS VPN packet through the provider core toward the appropriate egress PE router. It generally represents reachability to the egress PE or another transport endpoint. Once the packet reaches the egress portion of the path, the VPN label can be used to identify the appropriate customer VPN or VRF forwarding context. Route Distinguishers and Route Targets are control-plane constructs associated with VPN route identification and policy. The transport label therefore provides the core forwarding function needed to deliver the packet to the correct PE.

Question 35. Which BGP capability allows multiple valid paths for the same prefix to be advertised to a neighbor?

1. Route Reflection
2. Graceful Restart
3. Add-Path
4. Maximum-prefix

Correct Answer: 3. Add-Path

Explanation :-

BGP Add-Path allows a BGP speaker to advertise multiple paths for the same prefix rather than only one best path. This can improve path diversity and reduce situations where a route reflector hides alternate paths from downstream routers. Add-Path is useful in large service-provider networks where maintaining alternate routing information can improve convergence and resilience. Route Reflection addresses iBGP scalability, Graceful Restart supports forwarding continuity during certain control-plane restarts, and maximum-prefix limits the number of routes received. Add-Path therefore directly addresses the requirement to advertise multiple paths for one prefix.

Question 36. Which routing protocol uses Level-1 and Level-2 routers to create a hierarchical routing architecture?

1. OSPF
2. BGP
3. IS-IS
4. PIM

Correct Answer: 3. IS-IS

Explanation :-

IS-IS uses Level-1 and Level-2 routing to provide a hierarchical structure. Level-1 routers primarily route within an area, while Level-2 routers provide connectivity between areas. A Level-1-2 router can participate in both levels and commonly serves as the connection between the local area and the Level-2 backbone. OSPF uses areas and an Area 0 backbone rather than the Level-1/Level-2 terminology. BGP provides interdomain routing and PIM provides multicast routing. The IS-IS hierarchy is especially useful for building scalable service-provider IGP designs.

Question 37. Which mechanism allows an MPLS router to remove the top label before the packet reaches the egress PE?

1. RSVP signaling
2. Label imposition
3. Label swapping
4. Penultimate Hop Popping

Correct Answer: 4. Penultimate Hop Popping

Explanation :-

Penultimate Hop Popping (PHP) removes the outer MPLS label at the router immediately before the egress PE. This is commonly signaled using an implicit-null label and helps reduce label-processing work on the egress PE. The egress router can then process any remaining label, such as an MPLS VPN label, to determine the correct forwarding context. Label swapping replaces one label with another, while label imposition adds labels to traffic entering the MPLS domain. PHP is therefore an important MPLS forwarding optimization and a common topic in MPLS troubleshooting.

Question 38. A provider wants to use an MPLS traffic-engineering tunnel with an explicitly defined path. Which technology is traditionally associated with this requirement?

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

Correct Answer: 2. RSVP-TE

Explanation :-

RSVP-TE is traditionally used to establish MPLS Traffic Engineering tunnels with explicit path control. The provider can define constraints or an explicit path so that traffic does not necessarily follow the shortest path selected by the IGP. RSVP-TE also supports traffic-engineering features such as bandwidth reservations and fast reroute mechanisms. LDP normally follows IGP-selected paths, while IGMP and MSDP are multicast-related protocols. Although Segment Routing provides modern traffic-engineering capabilities without RSVP signaling, RSVP-TE remains an important technology within the CCNP Service Provider curriculum.

Question 39. Which multicast state represents traffic from a specific source to a specific multicast group?

1. (*,G)
2. (S,G)
3. (G,*)
4. (S,*)

Correct Answer: 2. (S,G)

Explanation :-

The PIM (S,G) state identifies multicast traffic from a specific source S to a specific multicast group G. It is commonly associated with a source-specific tree and is fundamental to PIM-SM operation after routers move from the shared tree toward a source tree. The (*,G) state represents a shared tree where the source is not yet specified. Understanding the distinction between these states helps engineers interpret multicast routing tables and troubleshoot missing or incorrectly forwarded multicast traffic. Source-specific multicast also uses the (S,G) model as its fundamental forwarding state.

Question 40. Which Segment Routing feature provides rapid local protection by steering traffic around a failed component before normal IGP convergence completes?

1. SRGB
2. Binding SID
3. TI-LFA
4. Node SID

Correct Answer: 3. TI-LFA

Explanation :-

Topology Independent Loop-Free Alternate (TI-LFA) provides fast local protection in Segment Routing networks. It precomputes repair paths that can be activated quickly when a protected link or node fails. This allows traffic to be redirected around the failure while the IGP performs its normal convergence process. The SRGB defines the range used for Segment Routing labels, a Binding SID identifies an SR Policy, and a Node SID identifies a node or prefix. TI-LFA is therefore the Segment Routing mechanism specifically designed to provide rapid local repair and improve service-provider convergence.