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

 

Question 1. Which routing protocol is commonly used as an Interior Gateway Protocol (IGP) in a service-provider network to provide topology information for MPLS LDP?

1. BGP
2. PIM
3. OSPF
4. IGMP

Correct Answer: 3. OSPF

Explanation :-

OSPF is an Interior Gateway Protocol that distributes topology and reachability information within an autonomous system. In an MPLS network using LDP, OSPF can provide the underlying IP reachability required for LDP to establish label bindings and create label-switched paths. LDP typically follows the paths selected by the IGP rather than independently calculating a traffic-engineered path. BGP is commonly used for interdomain routing and VPN route distribution, while PIM and IGMP support multicast operations. A stable IGP is therefore essential for reliable MPLS forwarding and LDP operation in a service-provider environment.

Question 2. An OSPF router has established a two-way relationship with a neighbor on a broadcast network but has not formed a full adjacency. Which condition commonly explains this behavior?

1. The routers are not required to become fully adjacent because they are not both DR or BDR
2. The OSPF process is using BGP authentication
3. The routers have different AS numbers
4. The MPLS label stack is incomplete

Correct Answer: 1. The routers are not required to become fully adjacent because they are not both DR or BDR

Explanation :-

On an OSPF broadcast network, not every router forms a full adjacency with every other router. Routers generally establish full adjacencies with the Designated Router (DR) and Backup Designated Router (BDR), while other routers may remain in the 2-Way state with one another. This behavior reduces the number of required adjacency relationships and limits unnecessary database exchange. Different AS numbers are relevant to BGP rather than OSPF adjacency formation. MPLS labels do not determine whether an OSPF neighbor reaches the Full state. The 2-Way state can therefore be normal on a broadcast segment.

Question 3. Which BGP attribute is generally preferred first when selecting the best path on Cisco IOS for routes learned through different sources?

1. MED
2. AS_PATH length
3. Origin type
4. Weight

Correct Answer: 4. Weight

Explanation :-

On Cisco IOS, BGP Weight is commonly considered before Local Preference and other standard path attributes in the best-path selection process. Weight is locally significant to the router and is not propagated to BGP neighbors. A higher weight is preferred. Local Preference is generally used to influence outbound path selection across an autonomous system, while AS_PATH length, origin type, and MED are considered later in the decision process. Because Weight is Cisco-specific and local to the router, administrators should distinguish it from attributes such as Local Preference that can be distributed through iBGP.

Question 4. Which MPLS component determines the outgoing label and forwarding action for an incoming label?

1. RIB
2. LFIB
3. ARP cache
4. BGP Loc-RIB

Correct Answer: 2. LFIB

Explanation :-

The Label Forwarding Information Base (LFIB) contains the label forwarding entries used to process MPLS packets. For an incoming label, the LFIB determines the forwarding action, such as label swapping, label popping, or label imposition, and identifies the outgoing interface or next hop. The RIB stores IP routing information, while the FIB contains IP forwarding entries. The BGP Loc-RIB contains routes selected by the BGP process. MPLS forwarding relies on the LFIB to make label-based forwarding decisions, making it a central component when troubleshooting label-switched paths and MPLS forwarding behavior.

Question 5. A provider wants to prefer one eBGP exit path over another for all routers within its autonomous system. Which attribute is most appropriate?

1. Local Preference
2. MED
3. Router ID
4. Origin

Correct Answer: 1. Local Preference

Explanation :-

BGP Local Preference is used to influence outbound path selection within an autonomous system. A higher Local Preference value is normally preferred, allowing a service provider to select a particular exit point for traffic leaving the AS. The attribute is propagated through iBGP and is commonly used to establish consistent outbound routing decisions across multiple routers. MED is generally used to influence how a neighboring AS selects among multiple entry points, while Router ID and Origin have different roles in BGP operation. Local Preference is therefore the appropriate attribute for controlling an internal preference for external exit paths.

Question 6. Which IS-IS level is primarily responsible for routing between different IS-IS areas?

1. Level 0
2. Level 1
3. Level 2
4. Level 3

Correct Answer: 3. Level 2

Explanation :-

IS-IS Level 2 routers provide routing between different IS-IS areas and form the backbone of the IS-IS routing domain. Level 1 routers primarily maintain routing information within their local area and typically use Level 2 connectivity to reach destinations outside that area. A router can operate as both Level 1 and Level 2, allowing it to provide intra-area and inter-area routing functions. IS-IS does not use the same area numbering model as OSPF, but the Level 1 and Level 2 hierarchy serves a comparable organizational purpose. Level 2 routing is therefore essential for inter-area connectivity.

Question 7. What is the primary purpose of the BGP next-hop-self configuration on an iBGP router?

1. To modify the AS_PATH length
2. To make the advertising router the next hop for the route
3. To disable route reflection
4. To increase the BGP hold timer

Correct Answer: 2. To make the advertising router the next hop for the route

Explanation :-

The BGP next-hop-self configuration causes the advertising router to set itself as the next-hop address for routes advertised to a neighbor. This is especially useful when an edge router learns routes from an eBGP peer and advertises them to an iBGP neighbor. Without appropriate next-hop reachability, the receiving router may learn the route but be unable to install it in the routing table. next-hop-self does not modify the AS_PATH, disable route reflection, or change BGP timers. It directly addresses next-hop reachability and is commonly used in service-provider iBGP designs.

Question 8. Which OSPF LSA type is originated by a router to describe its own links and interface information within an area?

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

Correct Answer: 4. Type 1

Explanation :-

An OSPF Type 1 LSA, known as a Router LSA, is originated by every OSPF router to describe its links, interfaces, and associated states within an area. All routers in the same area use Type 1 LSAs to build a consistent link-state database and calculate shortest paths using SPF. Type 3 LSAs advertise inter-area networks, Type 4 LSAs provide reachability information for an ASBR, and Type 5 LSAs describe external routes. Type 1 LSAs are therefore fundamental to the OSPF topology database and are used to represent the local router’s participation in the area.

Question 9. Which BGP community prevents a route from being advertised outside the local autonomous system while still allowing internal propagation?

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

Correct Answer: 3. NO_EXPORT

Explanation :-

The well-known BGP NO_EXPORT community instructs a BGP speaker not to advertise the associated route outside the local autonomous system. The route can still be propagated internally according to the applicable routing policy. This differs from NO_ADVERTISE, which prevents the route from being advertised to any BGP peer. Community attributes are useful for controlling route propagation and reducing accidental route leaks between customers, peers, and transit providers. Their behavior depends on the policies applied by the receiving and advertising routers, so administrators should verify that communities are preserved and acted upon as intended.

Question 10. Which protocol is responsible for distributing labels in a conventional MPLS network that follows IGP-selected paths?

1. LDP
2. MSDP
3. BFD
4. IGMP

Correct Answer: 1. LDP

Explanation :-

Label Distribution Protocol (LDP) distributes MPLS labels for forwarding equivalence classes, typically using the reachability information provided by an IGP such as OSPF or IS-IS. LDP establishes sessions with neighboring routers and exchanges label bindings that support label-switched paths. Unlike RSVP-TE, LDP does not normally establish explicitly traffic-engineered paths. BFD is used for fast failure detection, MSDP supports multicast source discovery, and IGMP manages multicast group membership between hosts and routers. LDP is therefore the conventional protocol used to establish label distribution along IGP-selected routes.

Question 11. A BGP router receives multiple routes to the same destination. Which attribute generally has higher preference in Cisco BGP selection?

1. MED
2. Origin type
3. AS_PATH length
4. Local Preference

Correct Answer: 4. Local Preference

Explanation :-

In the Cisco BGP best-path selection process, Local Preference is generally considered before AS_PATH length, origin type, and MED. A higher Local Preference value is preferred and is used to influence outbound traffic selection within the autonomous system. This attribute is particularly useful when a provider wants all internal routers to favor a specific exit path. MED is usually evaluated later and is commonly used to communicate an entry-point preference between neighboring autonomous systems. The exact best-path process can include platform-specific rules and additional attributes, but Local Preference is a major path-selection factor.

Question 12. Which IS-IS mechanism allows a router to advertise a default route from Level 2 into its Level-1 area?

1. Level-1 default route behavior
2. BGP route reflection
3. OSPF Type 5 translation
4. PIM Register

Correct Answer: 1. Level-1 default route behavior

Explanation :-

An IS-IS Level-1 router generally needs a way to reach destinations outside its local area. A Level-1-2 router can provide a default route toward the Level-2 backbone, allowing Level-1 routers to forward traffic for destinations not present in their local database. This hierarchical behavior reduces the need for every Level-1 router to maintain complete inter-area routing information. BGP route reflection, OSPF Type 5 translation, and PIM Register perform unrelated functions. Understanding the Level-1 default route behavior is important when troubleshooting inter-area reachability and routing decisions in IS-IS networks.

Question 13. Which PIM-SM tree state represents traffic from any source toward a multicast group through the shared tree?

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

Correct Answer: 2. (*,G)

Explanation :-

In PIM Sparse Mode, the (*,G) state represents a shared-tree entry for multicast group G, where the source is not yet specified. The shared tree is normally rooted at the Rendezvous Point (RP). When routers learn a specific source and transition to a source-specific tree, they use (S,G) state, where S identifies the source and G identifies the multicast group. Understanding these state formats is essential when interpreting multicast routing tables and troubleshooting PIM-SM forwarding. The (*,G) entry is associated with shared-tree operation rather than a specific source tree.

Question 14. Which MPLS label operation removes the outer transport label at the router immediately before the egress PE?

1. Label imposition
2. Label swapping
3. Penultimate Hop Popping
4. Label stacking

Correct Answer: 3. Penultimate Hop Popping

Explanation :-

Penultimate Hop Popping (PHP) removes the outer MPLS transport label at the penultimate router, which is the router immediately before the egress PE. This operation reduces the label-processing responsibility of the egress router and is commonly associated with implicit-null label signaling. In an MPLS L3VPN, the inner VPN label may remain in the packet so that the egress PE can select the correct VRF or VPN forwarding entry. Label swapping replaces an incoming label with another label, while label imposition adds labels to traffic entering an MPLS forwarding path.

Question 15. Which BGP feature is designed to reduce the impact of receiving an unexpectedly large number of prefixes from a neighbor?

1. Maximum-prefix limit
2. Route reflector
3. Add-Path
4. MED

Correct Answer: 1. Maximum-prefix limit

Explanation :-

The BGP maximum-prefix feature allows an administrator to limit the number of prefixes accepted from a BGP neighbor. This protects the router against accidental route leaks, configuration errors, and unexpectedly large routing tables. Depending on the platform and configuration, the router can generate warnings or take action when the configured threshold is exceeded. Route reflection addresses iBGP scalability, Add-Path permits multiple paths to be advertised, and MED influences route selection. Maximum-prefix protection is particularly important for service providers because receiving excessive routes can consume memory and processing resources.

Question 16. Which Segment Routing identifier is normally associated with a specific adjacency between two routers?

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

Correct Answer: 2. Adjacency SID

Explanation :-

An Adjacency SID identifies a specific adjacency or link from a Segment Routing router. By using an Adjacency SID, traffic can be instructed to follow a particular link rather than simply forwarding toward a destination node using the shortest path. This provides more precise traffic-engineering control. A Node SID identifies a node or prefix, a Binding SID represents an SR Policy, and an Anycast SID can identify a set of nodes sharing an anycast function. Adjacency SIDs are especially useful in SR-TE policies requiring explicit control over particular links or paths.

Question 17. In an MPLS L3VPN, which component controls whether a route exported from one VRF is imported into another VRF?

1. Route Distinguisher
2. MPLS transport label
3. Route Target
4. OSPF router ID

Correct Answer: 3. Route Target

Explanation :-

Route Targets (RTs) are extended BGP communities used to control the import and export of VPN routes between VRFs. When a route is exported from a VRF, one or more RTs are attached to it. A receiving VRF imports the route when its configured import policy matches the route’s RT. The Route Distinguisher serves a different purpose by making overlapping VPN prefixes unique in the MP-BGP address space. MPLS transport labels provide packet forwarding through the core, and OSPF router IDs identify OSPF speakers. Route Targets therefore control VPN route distribution between VRFs.

Question 18. Which protocol provides rapid detection of forwarding-path failures and can be integrated with OSPF, IS-IS, or BGP?

1. BFD
2. SNMP
3. NTP
4. Syslog

Correct Answer: 1. BFD

Explanation :-

Bidirectional Forwarding Detection (BFD) is designed to detect forwarding-path failures quickly and can work with routing protocols such as OSPF, IS-IS, and BGP. BFD sessions exchange control packets at configured intervals and detect failures independently of slower routing-protocol timers. When a BFD session goes down, the associated routing protocol can respond by removing or recalculating routes. SNMP is primarily used for monitoring, NTP synchronizes system clocks, and Syslog records operational messages. BFD is therefore a key convergence technology in service-provider networks that require rapid failure detection.

Question 19. Which BGP attribute is used to record the autonomous systems through which a route advertisement has passed?

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

Correct Answer: 2. AS_PATH

Explanation :-

The AS_PATH attribute records the sequence of autonomous systems that a BGP route advertisement has traversed. It is used for loop prevention because a BGP router generally rejects a route when its own autonomous-system number appears in the path. AS_PATH length can also influence the best-path decision, although other attributes may be evaluated earlier. NEXT_HOP identifies the address used to reach the destination, Local Preference influences outbound path selection within an AS, and MED provides an entry-point preference to a neighboring AS. AS_PATH is therefore fundamental to interdomain routing and BGP loop prevention.

Question 20. In PIM-SM, which mechanism is used to resolve duplicate multicast forwarding on a shared multi-access network?

1. PIM Register
2. PIM Join
3. PIM Bootstrap
4. PIM Assert

Correct Answer: 4. PIM Assert

Explanation :-

PIM Assert is used when multiple multicast routers on a shared network segment could forward the same multicast traffic. The routers exchange Assert messages and select one forwarding router for the affected multicast flow, preventing duplicate forwarding on the segment. PIM Register is used by a source’s designated router to register traffic with the RP, while PIM Join messages build multicast distribution trees. PIM Bootstrap is associated with RP discovery and distribution. Assert processing is therefore important for maintaining efficient multicast forwarding on multi-access networks with multiple potential forwarders.