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

 

Question 121. A service provider router is configured as an IS-IS Level-1-2 router. Which behavior allows it to provide connectivity between the Level-1 and Level-2 portions of the IS-IS domain?

1. It disables all Level-1 adjacencies
2. It maintains separate Level-1 and Level-2 link-state databases and can route between the levels
3. It converts every Level-1 LSP into an OSPF LSA
4. It advertises only Level-1 routes to external autonomous systems

Correct Answer: 2. It maintains separate Level-1 and Level-2 link-state databases and can route between the levels

Explanation :-

An IS-IS Level-1-2 router participates in both routing levels and maintains separate link-state information for Level-1 and Level-2 operation. Level-1 routing provides connectivity within an area, while Level-2 routing provides inter-area connectivity across the IS-IS domain. A Level-1 router that needs to reach a destination outside its area can use a Level-1-2 router as the path toward the Level-2 backbone. This hierarchical architecture helps service-provider networks scale by limiting detailed topology information to the appropriate routing level. The Level-1-2 router therefore acts as the important connection point between local Level-1 routing and the broader Level-2 topology.

Question 122. An OSPF adjacency between two routers on a broadcast network remains in the 2-Way state. Both routers are DROTHERs. What is the most likely explanation?

1. The routers have incompatible OSPF area IDs
2. The routers have mismatched authentication keys
3. The OSPF process is disabled on one router
4. The routers have reached the expected 2-Way state because neither is the DR or BDR

Correct Answer: 4. The routers have reached the expected 2-Way state because neither is the DR or BDR

Explanation :-

On a broadcast OSPF network such as Ethernet, routers elect a Designated Router (DR) and Backup Designated Router (BDR). DROTHER routers establish full adjacencies with the DR and BDR, but two DROTHER routers normally remain in the 2-Way state with each other. The 2-Way state indicates that bidirectional communication has been established and each router sees the other in its Hello messages. Therefore, seeing a DROTHER-to-DROTHER relationship in 2-Way is normally expected behavior rather than an adjacency failure. Troubleshooting should focus on later states only when routers that should become fully adjacent fail to progress appropriately.

Question 123. A BGP administrator wants to advertise a customer’s routes to an upstream provider while preventing those routes from being advertised beyond the provider’s autonomous system. Which BGP community is appropriate?

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

Correct Answer: 1. NO_EXPORT

Explanation :-

The well-known BGP NO_EXPORT community tells a receiving autonomous system that a route carrying the community should not be advertised outside that autonomous system. This is useful when a provider accepts a route but wants to prevent propagation to external autonomous systems. NO_ADVERTISE is more restrictive because a route carrying it should not be advertised to any BGP peer. The distinction is important when designing provider and customer routing policies. NO_EXPORT allows the route to circulate within the receiving AS according to local policy while preventing further external propagation. The actual enforcement also depends on the provider’s BGP policy configuration and treatment of communities.

Question 124. A BGP speaker receives two otherwise equivalent routes to the same destination. One route has a higher LOCAL_PREF value than the other. Which route-selection behavior should normally occur?

1. The route with the lower LOCAL_PREF is preferred
2. LOCAL_PREF is ignored for iBGP routes
3. The route with the higher LOCAL_PREF is preferred
4. The route with the shortest MED is always preferred first

Correct Answer: 3. The route with the higher LOCAL_PREF is preferred

Explanation :-

BGP LOCAL_PREF is used within an autonomous system to influence the preferred exit point for outbound traffic. When comparing otherwise eligible BGP paths, a higher LOCAL_PREF value is preferred. This attribute is propagated through iBGP and is normally used to establish consistent outbound routing decisions across routers in the autonomous system. For example, an organization can assign a higher LOCAL_PREF to routes learned through its preferred transit provider. LOCAL_PREF is different from MED, which is generally used to influence how neighboring autonomous systems select among multiple entry points. Proper policy design should therefore consider whether the desired traffic-engineering direction is inbound or outbound.

Question 125. A network engineer needs to determine which labels are actually programmed for packet forwarding on a Cisco MPLS router. Which structure should be examined?

1. The OSPF LSDB
2. The BGP RIB only
3. The IS-IS adjacency database
4. The MPLS Label Forwarding Information Base (LFIB)

Correct Answer: 4. The MPLS Label Forwarding Information Base (LFIB)

Explanation :-

The MPLS Label Forwarding Information Base (LFIB) contains the label forwarding information used by the router’s forwarding plane. It associates incoming labels with actions such as swap, pop, or push and identifies the appropriate outgoing interface and next-hop information. The Label Information Base (LIB), in contrast, contains label bindings learned or generated by label-distribution mechanisms and represents the control-plane view. During MPLS troubleshooting, examining the LFIB helps determine whether the required forwarding entries have actually been installed. A correct RIB or LIB entry does not necessarily prove that the forwarding plane has the expected MPLS operation.

Question 126. A provider uses BGP route reflection to reduce the number of iBGP sessions. A route reflector receives a route from one of its clients. To which iBGP peers can the route reflector advertise that route?

1. Only to the originating client
2. To other clients and non-client iBGP peers, subject to route-reflection rules
3. Only to eBGP peers
4. It cannot advertise client-learned routes

Correct Answer: 2. To other clients and non-client iBGP peers, subject to route-reflection rules

Explanation :-

BGP route reflection modifies the normal iBGP propagation restriction so that an iBGP route received by a route reflector can be advertised to other appropriate iBGP peers. When a route is learned from a route-reflector client, the reflector can advertise it to other clients and non-client iBGP peers, subject to the route-reflection rules and normal BGP policy. This removes the requirement for a full mesh of iBGP sessions between every router. Route reflection also adds attributes such as ORIGINATOR_ID and CLUSTER_LIST to help prevent routing loops. Correctly defining client relationships is therefore important when designing a scalable provider BGP topology.

Question 127. In an MPLS Layer 3 VPN, what is the primary purpose of the Route Distinguisher (RD)?

1. To make otherwise identical VPN prefixes globally unique in the VPNv4 or VPNv6 address space
2. To determine which VRF imports the route
3. To encrypt customer traffic
4. To identify the MPLS transport LSP

Correct Answer: 1. To make otherwise identical VPN prefixes globally unique in the VPNv4 or VPNv6 address space

Explanation :-

The Route Distinguisher (RD) is used in MPLS Layer 3 VPNs to create globally unique VPN routes from potentially overlapping customer prefixes. For example, multiple customers can independently use the same IPv4 prefix, such as 10.10.10.0/24. By combining the prefix with a unique RD, the provider can represent each route distinctly in the VPNv4 address family. The RD provides uniqueness but does not determine which VRF receives the route. Route Targets perform the import and export policy function. Keeping these roles separate is fundamental to understanding MPLS L3VPN control-plane operation and troubleshooting incorrect VPN route distribution.

Question 128. A provider wants a BGP route learned from one eBGP peer to appear with the local router as the next hop when advertised to an iBGP peer. Which configuration feature is commonly used?

1. ebgp-multihop
2. maximum-paths
3. next-hop-self
4. route-reflector-client

Correct Answer: 3. next-hop-self

Explanation :-

By default, when a BGP router advertises an eBGP-learned route to an iBGP peer, the original next-hop attribute may be preserved. If the iBGP peer cannot reach that next-hop address through the provider’s IGP, the route may be present in BGP but unusable for forwarding. Applying next-hop-self causes the advertising router to set itself as the BGP next hop for the advertised route. This is commonly used on provider edge or internal BGP routers where the receiving router should forward traffic toward the advertising router. The underlying IGP must still provide reachability to the new next-hop address.

Question 129. A Cisco router running BGP shows a neighbor in the Active state. Which underlying condition should be investigated first?

1. Whether the router has learned too many OSPF Type 5 LSAs
2. Whether TCP connectivity to the BGP neighbor’s address can be established
3. Whether MPLS PHP is disabled
4. Whether the PIM RP has changed

Correct Answer: 2. Whether TCP connectivity to the BGP neighbor’s address can be established

Explanation :-

BGP uses TCP port 179 for its sessions. A neighbor remaining in the Active state can indicate that the router is attempting to establish the TCP connection but is not successfully completing the process. Troubleshooting should therefore include IP reachability, routing to the neighbor address, TCP port 179 filtering, access-control policies, source-interface configuration, and multihop requirements where applicable. The Active state does not mean that the BGP session is functioning normally; it is a sign that connection establishment is being attempted or retried. Verifying basic IP and TCP connectivity provides a logical first step before investigating higher-level BGP policy.

Question 130. In Segment Routing using SR-MPLS, what does an Adjacency SID normally identify?

1. A customer VRF
2. A BGP autonomous system
3. An entire OSPF area
4. A specific adjacency or link that the packet should traverse

Correct Answer: 4. A specific adjacency or link that the packet should traverse

Explanation :-

An Adjacency SID represents a specific adjacency or outgoing link associated with a Segment Routing-capable node. When included in an SR policy’s segment list, it can instruct traffic to traverse a particular link rather than simply reaching a destination node. This provides finer-grained path control than a Node SID, which generally represents reachability to a node. Adjacency SIDs are particularly useful for traffic engineering and explicit path construction. Their allocation and forwarding behavior depend on the Segment Routing implementation and protocol extensions used by the network. Understanding the distinction between Node SIDs and Adjacency SIDs is important when troubleshooting SR policy paths.

Question 131. An operator observes that an MPLS packet enters a router with label 240 but leaves with label 315. Which MPLS forwarding operation is represented?

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

Correct Answer: 3. Swap

Explanation :-

MPLS label swapping occurs when a router receives a packet with one incoming label and replaces it with a different outgoing label before forwarding the packet. In the example, label 240 is replaced with label 315, which is a classic label-swap operation. A push operation would add a new label to the stack, while a pop operation would remove a label. Penultimate-hop popping is a specific form of pop performed by the router before the egress LSR, usually to remove the transport label before the packet reaches the egress. Examining incoming and outgoing label values is therefore a useful way to identify MPLS forwarding actions.

Question 132. A network administrator wants BGP to stop accepting additional routes from a neighbor after the number of received prefixes exceeds a configured threshold. Which feature provides this protection?

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

Correct Answer: 1. BGP maximum-prefix

Explanation :-

The BGP maximum-prefix feature limits the number of prefixes that a router will accept from a particular BGP neighbor. It provides protection against unexpected route growth, configuration mistakes, or route leaks that could consume significant memory and processing resources. When the configured threshold is exceeded, the router can take a configured protective action, such as shutting down or resetting the BGP session depending on the implementation and settings. The feature should be configured with thresholds appropriate for the expected routing table size. Monitoring and carefully selecting warning or restart behavior can help avoid unnecessary service disruption while still providing protection.

Question 133. Which BGP capability allows a router to advertise multiple paths for the same prefix instead of restricting advertisements to a single selected path?

1. Route dampening
2. MED
3. Route reflection
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 to a neighbor. Standard BGP behavior generally advertises only the selected best path for a destination, which can limit the amount of path information available to downstream routers. Add-Path can improve path diversity and help reduce issues such as path hiding, especially in networks using route reflection. The exact number and selection of additional paths depend on the negotiated capability and configured policy. It is therefore useful in service-provider environments where maintaining multiple usable paths can improve resilience, traffic engineering, and convergence behavior.

Question 134. A service-provider network uses PIM-SM. A receiver sends a Join for a multicast source-specific tree after learning the source address. Which multicast state is associated with that source and group?

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

Correct Answer: 2. (S,G)

Explanation :-

In PIM-SM, (S,G) state represents a specific multicast source S and multicast group G. This state is used when routers build a source-specific shortest-path tree toward the sender. By contrast, (*,G) represents shared-tree state for a multicast group without identifying a specific source. When a receiver or downstream router explicitly joins a source, the resulting source-specific state is represented as (S,G). Understanding these two forms of multicast state is essential when troubleshooting PIM-SM forwarding, RPF decisions, and transitions from a shared tree through the Rendezvous Point to a source-specific tree.

Question 135. An IS-IS router is marked with the overload bit. What routing behavior is generally intended by this condition?

1. Other routers should prefer it as the primary transit router
2. The router should immediately terminate all IS-IS adjacencies
3. Other routers should avoid using it as a transit path while still allowing reachability to its own destinations as appropriate
4. The router must become the DIS

Correct Answer: 3. Other routers should avoid using it as a transit path while still allowing reachability to its own destinations as appropriate

Explanation :-

The IS-IS overload bit indicates that a router should generally not be selected as a transit router for traffic through the network. This can be useful during startup, synchronization, or periods when the router’s routing information is incomplete. Other routers can take alternate paths while still maintaining reachability to destinations directly associated with the overloaded router, depending on the network’s routing design and implementation. The overload condition therefore helps prevent traffic from being forwarded through a router that is not ready to provide reliable transit service. It is particularly useful during controlled convergence and operational maintenance procedures.

Question 136. An OSPF router is configured as an NSSA router and needs to advertise an external route learned from another routing protocol into the NSSA. Which LSA type is normally used for the external route within the NSSA?

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

Correct Answer: 1. Type 7

Explanation :-

An OSPF Not-So-Stubby Area (NSSA) permits controlled external route redistribution while restricting the normal flooding of Type 5 external LSAs into the area. External routes introduced within the NSSA are represented using Type 7 LSAs. An NSSA ABR can translate eligible Type 7 LSAs into Type 5 LSAs so that the external routes can be advertised into the rest of the OSPF domain. This design allows an area to retain stub-like characteristics while still supporting local route redistribution. During troubleshooting, checking Type 7 LSAs and their translation behavior is important when an external route is visible inside the NSSA but missing from other OSPF areas.

Question 137. A BGP administrator wants to prevent a route from being advertised to any other BGP peer after it is received. Which well-known community should be applied?

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

Correct Answer: 2. NO_ADVERTISE

Explanation :-

The NO_ADVERTISE BGP community indicates that a route should not be advertised to any other BGP peer. This is more restrictive than NO_EXPORT. NO_EXPORT permits propagation within the receiving autonomous system while preventing advertisement outside that AS, whereas NO_ADVERTISE suppresses advertisement to BGP peers altogether. These well-known communities are commonly used to implement routing-control policies without requiring a custom community value. Network operators should still verify how their specific Cisco configuration handles communities, because receiving, preserving, or modifying a community can depend on route-policy configuration and the capabilities negotiated between BGP peers.

Question 138. A provider uses BFD to accelerate failure detection for a BGP session. What is the primary benefit of integrating BFD with BGP?

1. BFD selects the BGP best path
2. BFD replaces BGP route advertisements
3. BFD provides a faster mechanism for detecting forwarding-path failure than waiting for normal BGP timers
4. BFD assigns MPLS labels to BGP routes

Correct Answer: 4. BFD provides a faster mechanism for detecting forwarding-path failure than waiting for normal BGP timers

Explanation :-

Bidirectional Forwarding Detection (BFD) provides rapid detection of failures in the forwarding path. When BFD is integrated with BGP, a failure can be detected much faster than relying solely on standard BGP hold and keepalive timers. BGP can then react by bringing the affected session down and recalculating available routes. BFD does not perform BGP path selection, distribute prefixes, or assign MPLS labels. Its role is focused on fast liveliness and forwarding-path failure detection. In service-provider networks, combining BFD with routing protocols can significantly reduce convergence time when a link or forwarding path becomes unavailable.

Question 139. In an MPLS Layer 3 VPN, a PE router receives a VPN route carrying a Route Target that matches the import policy of a particular VRF. What is the expected result?

1. The route can be imported into that VRF
2. The route is converted into an OSPF Type 7 LSA
3. The route is automatically exported to every VRF
4. The Route Distinguisher is removed and the route is discarded

Correct Answer: 1. The route can be imported into that VRF

Explanation :-

Route Targets (RTs) control the import and export of VPN routes between provider edge routers and VRFs. When a VPN route carries an RT that matches the import RT configured for a VRF, that route is eligible to be imported into the VRF’s routing table. The Route Distinguisher and Route Target have different purposes: the RD makes overlapping VPN prefixes unique, while the RT controls membership and route distribution between VRFs. Multiple VRFs can import the same RT, enabling controlled connectivity between customer sites when required. Troubleshooting VPN route visibility therefore requires checking both the route’s RT attributes and the VRF’s import policy.

Question 140. A multicast packet arrives at a router through an interface that is not the expected reverse-path interface for the source. What will PIM generally do with the packet?

1. Forward it immediately to all PIM neighbors
2. Send it to the BGP route reflector
3. Encapsulate it in an MPLS label automatically
4. Drop it because the packet fails the multicast RPF check

Correct Answer: 4. Drop it because the packet fails the multicast RPF check

Explanation :-

PIM multicast forwarding relies on Reverse Path Forwarding (RPF) checks to prevent forwarding loops and incorrect multicast traffic paths. For a multicast packet from source S, the router determines the expected incoming interface using its unicast routing information toward S. If the packet arrives on a different interface, the RPF check fails and the router normally drops the packet rather than forwarding it. Troubleshooting an RPF failure involves checking the unicast route toward the source, multicast routing state, routing preferences, and interface connectivity. Correct unicast reachability is therefore a critical foundation for reliable PIM multicast forwarding.