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

 

Question 201. An engineer is troubleshooting an IS-IS adjacency that remains in the Up state, but routes learned through the neighbor are not being installed because the neighbor has been configured with the overload bit. What does the overload bit indicate?

1. The neighbor is intentionally signaling that it should not be used as a transit router
2. The neighbor has disabled all IS-IS Hello messages
3. The neighbor has become overloaded and should generally not be selected as a transit path
4. The neighbor has converted from Level 2 to Level 1 operation

Correct Answer: 3. The neighbor has become overloaded and should generally not be selected as a transit path

Explanation :-

The IS-IS overload bit allows a router to signal that it should not be used as a transit path while it may still need to advertise its directly connected destinations. This is commonly useful during startup, resource exhaustion, or other conditions where the router cannot reliably provide transit forwarding. Other IS-IS routers can use the overload indication when calculating paths and avoid selecting the overloaded router as an intermediate transit node. The adjacency itself can remain operational, so seeing an Up adjacency does not necessarily mean the router should be preferred for transit traffic.

Question 202. An OSPF network contains several routers connected through an Ethernet segment. Two DROTHER routers establish a 2-Way relationship rather than progressing directly to Full. What is the expected reason for this behavior?

1. Only the DR and BDR normally form Full adjacencies with DROTHER routers
2. OSPF authentication is preventing the routers from exchanging LSAs
3. The routers have mismatched OSPF area IDs
4. The interfaces are operating as point-to-point links

Correct Answer: 1. Only the DR and BDR normally form Full adjacencies with DROTHER routers

Explanation :-

On a broadcast multiaccess OSPF network, routers elect a Designated Router and Backup Designated Router to reduce the number of full adjacencies required. A DROTHER normally establishes Full adjacency with the DR and BDR, while two DROTHER routers typically remain in the 2-Way state with each other. This behavior is normal and does not indicate an OSPF failure. The 2-Way state confirms that the routers have successfully exchanged Hellos and recognize one another, while database synchronization between DROTHER routers is normally handled through the DR and BDR.

Question 203. A service provider wants to advertise only selected customer prefixes from a BGP routing table to a peer. Which configuration mechanism provides granular prefix-based control for this outbound advertisement?

1. BGP keepalive timer
2. MED attribute
3. Prefix list applied through a routing policy
4. BGP router ID

Correct Answer: 3. Prefix list applied through a routing policy

Explanation :-

A prefix list combined with a routing policy provides precise control over which prefixes are accepted or advertised. The prefix list defines the matching prefixes, prefix lengths, or ranges, while the routing policy determines how matching routes are handled. For example, a provider can permit a customer’s approved aggregate and specific subnets while denying all other routes. BGP attributes such as MED influence path selection but do not inherently provide the same granular prefix filtering capability. Router ID and keepalive settings are unrelated to selecting specific prefixes for outbound advertisement.

Question 204. Two PE routers exchange VPNv4 routes using MP-BGP. A VPN route contains an IPv4 prefix that overlaps with a prefix belonging to another customer. Which MPLS L3VPN component allows the overlapping prefixes to remain unique in the VPNv4 address space?

1. Route Target
2. Route Distinguisher
3. Label Distribution Protocol
4. BGP community

Correct Answer: 2. Route Distinguisher

Explanation :-

The Route Distinguisher, or RD, makes otherwise identical IPv4 prefixes unique within the VPNv4 address family. For example, two different customers can both use 10.10.10.0/24, but their VPNv4 routes can remain distinct because different RDs are prepended to those IPv4 prefixes. The RD provides uniqueness and does not itself determine which VRFs import a route. Route Targets perform the import and export policy function. MPLS labels provide forwarding separation, while BGP communities can carry additional policy information but do not replace the RD’s uniqueness function.

Question 205. A BGP router receives two routes to the same destination. Both routes have identical LOCAL_PREF, AS_PATH, origin, and MED values. One route is learned through eBGP and the other through iBGP. Which route is normally preferred at this stage of Cisco BGP best-path selection?

1. The eBGP-learned route
2. The iBGP-learned route
3. Both routes are automatically installed using ECMP
4. The route with the higher BGP router ID is always selected first

Correct Answer: 1. The eBGP-learned route

Explanation :-

Cisco BGP considers whether a path was learned through eBGP or iBGP after several earlier path attributes have been evaluated. When the relevant preceding attributes are equal, an eBGP path is preferred over an iBGP path. This behavior is important in service-provider networks because an externally learned route can therefore be selected over an otherwise equivalent internally learned route. BGP does not automatically install both paths unless the configuration and platform support appropriate multipath conditions. Router ID is used in later tie-breaking rather than being the immediate deciding factor in this situation.

Question 206. An MPLS router receives a packet with an incoming label and needs to determine the outgoing label, next hop, and outgoing interface. Which forwarding structure provides this information?

1. LIB
2. RIB
3. LFIB
4. BGP Loc-RIB

Correct Answer: 3. LFIB

Explanation :-

The Label Forwarding Information Base, or LFIB, is used for actual MPLS forwarding decisions. It contains information such as the incoming label, outgoing label operation, next-hop information, and outgoing interface. The Label Information Base, or LIB, stores label bindings learned from label distribution mechanisms, but the LFIB is the forwarding structure used to perform label operations in the data plane. The IP Routing Information Base is used for IP routing decisions and does not directly provide the complete MPLS label-forwarding operation for an incoming labeled packet.

Question 207. A network uses Segment Routing over MPLS. An engineer wants traffic to follow a specific adjacency between two routers rather than simply reaching a destination node. Which SID type should be used to explicitly represent that link?

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

Correct Answer: 4. Adjacency SID

Explanation :-

An Adjacency SID represents a specific adjacency or link from a Segment Routing node. When included in a segment list, it can steer traffic over that particular link rather than relying solely on the shortest path toward a destination node. A Node SID represents reachability to a node or prefix and normally allows the routing topology to determine the path. A Binding SID identifies a segment-routing policy or bound segment list, while a Prefix-SID is associated with a prefix. Adjacency SIDs are therefore particularly useful when explicit link-level steering is required.

Question 208. A BGP session is established, but the router does not install a received route because the BGP NEXT_HOP address is unreachable in the routing table. What should the engineer verify first?

1. The BGP router ID length
2. Underlying IGP or static reachability to the BGP next hop
3. The BGP hold timer only
4. The local MED value

Correct Answer: 2. Underlying IGP or static reachability to the BGP next hop

Explanation :-

BGP generally requires the next-hop address of a received route to be reachable before the route can be considered usable for forwarding. In a service-provider network, this reachability is commonly provided by an IGP such as OSPF or IS-IS, or by an appropriate static route. A BGP session can remain Established even when individual routes are unusable because their next hops are unresolved. Engineers should therefore verify the routing table, IGP advertisements, and next-hop reachability before changing unrelated BGP attributes such as MED or timers.

Question 209. A provider wants to prevent a customer-learned prefix from being advertised to an unauthorized external peer. Which approach directly addresses this requirement?

1. Increase the BGP hold timer
2. Enable BGP route dampening
3. Apply an outbound prefix filter or routing policy
4. Change the OSPF router priority

Correct Answer: 3. Apply an outbound prefix filter or routing policy

Explanation :-

Outbound prefix filtering is a fundamental method for controlling which routes a provider advertises to an external BGP peer. A prefix list can identify permitted customer prefixes, and a route policy can then explicitly permit or deny those routes. This helps prevent accidental route leaks and limits advertisements to the intended routing scope. BGP route dampening addresses route instability rather than advertisement authorization. OSPF router priority affects DR/BDR election on applicable OSPF networks, and the BGP hold timer controls session failure detection rather than route-policy selection.

Question 210. In an MPLS L3VPN, a PE router exports a customer route with a specific Route Target. A remote PE has a VRF configured with an import Route Target that does not match the exported value. What is the expected result?

1. The remote VRF does not import the VPN route
2. The route is imported automatically because all VPNv4 routes are global
3. The remote PE changes the RD to force an import
4. The route is imported but without its VPN label

Correct Answer: 1. The remote VRF does not import the VPN route

Explanation :-

Route Targets control VPN route import and export policy. When a PE exports a VPN route, it attaches one or more Route Target extended communities. A receiving VRF imports the route only when its configured import policy matches an appropriate Route Target. If there is no match, the route can exist in the VPNv4 BGP table but will not be installed into that VRF. The Route Distinguisher provides prefix uniqueness and does not determine VRF membership. Therefore, an RT mismatch is a common cause of missing routes between customer VPN sites.

Question 211. A BGP administrator wants to provide multiple valid paths for a prefix to downstream routers instead of having BGP advertise only its single best path. Which feature can provide this capability?

1. BGP route dampening
2. BGP maximum-prefix
3. BGP graceful restart
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 prefix rather than only one best path. This can improve path diversity and provide downstream routers with additional alternatives, which can be useful for faster convergence and traffic engineering. Standard BGP behavior normally advertises only the selected best path to a neighbor. Maximum-prefix protects a session from excessive route advertisements, route dampening addresses unstable routes, and graceful restart helps preserve forwarding during certain control-plane restart conditions. Add-Path specifically addresses the ability to advertise multiple paths.

Question 212. An OSPF router is configured as an NSSA router and learns an external route from another routing domain. Which LSA type is initially used to represent that external route inside the NSSA?

1. Type 3 LSA
2. Type 7 LSA
3. Type 4 LSA
4. Type 2 LSA

Correct Answer: 2. Type 7 LSA

Explanation :-

An OSPF Not-So-Stubby Area, or NSSA, permits external route redistribution while retaining characteristics that limit certain external LSAs. External routes introduced inside the NSSA are represented using Type 7 LSAs. When necessary, an NSSA ABR can translate appropriate Type 7 LSAs into Type 5 LSAs so that the external routes can be propagated into the rest of the OSPF domain. Type 3 LSAs describe inter-area networks, Type 4 LSAs identify reachability to an ASBR, and Type 2 LSAs represent transit-network information associated with a DR.

Question 213. An engineer is configuring BGP between two routers using their loopback addresses. The routers are not directly connected, and the BGP session fails because the TCP connection cannot be established. Which configuration is commonly required for an eBGP loopback peering session?

1. eBGP multihop
2. OSPF passive-interface
3. BGP Add-Path
4. MPLS PHP

Correct Answer: 1. eBGP multihop

Explanation :-

When eBGP peers use loopback addresses rather than directly connected interfaces, the BGP TCP session may require a TTL greater than the default single-hop value. The ebgp-multihop configuration allows the router to accept and originate eBGP sessions across multiple routed hops. The underlying network must also provide IP reachability to the peer loopback addresses. Add-Path concerns advertisement of multiple BGP paths, PHP concerns MPLS label disposition, and OSPF passive-interface controls OSPF neighbor formation. Therefore, eBGP multihop is a key configuration consideration for loopback-based eBGP peering.

Question 214. A service-provider router receives several BGP paths for the same destination. The administrator wants to influence which exit point is selected for outbound traffic from the autonomous system. Which BGP attribute is normally designed for this purpose?

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

Correct Answer: 3. LOCAL_PREF

Explanation :-

BGP LOCAL_PREF is commonly used within an autonomous system to influence the preferred exit point for outbound traffic. A higher LOCAL_PREF is preferred over a lower value when comparing otherwise eligible BGP paths. Because the attribute is propagated through iBGP, it can provide consistent outbound path selection across the autonomous system. AS_PATH can influence path selection and is often manipulated to affect inbound traffic, while MED can provide a neighboring AS with information about preferred entry points under applicable conditions. NEXT_HOP identifies the forwarding next hop rather than serving as the primary outbound-exit policy mechanism.

Question 215. An MPLS router receives a labeled packet and determines that the top label should be removed before the packet is forwarded toward the next router. Which MPLS operation is being performed?

1. Push
2. Swap
3. Pop
4. Imposition

Correct Answer: 3. Pop

Explanation :-

The MPLS pop operation removes the top label from an MPLS label stack. This is commonly associated with penultimate hop popping, where the router immediately before the egress LER removes the transport label so that the egress router can process the packet without performing that label lookup. A push operation adds a label to the stack, while swap replaces the incoming top label with another outgoing label. Understanding these operations is important when troubleshooting MPLS forwarding because they describe the exact label-stack transformation performed at each forwarding hop.

Question 216. A PIM-SM router has learned a multicast route but rejects incoming multicast packets because the unicast routing table identifies a different interface as the best reverse path toward the source. What condition is occurring?

1. PIM Assert election
2. Reverse Path Forwarding failure
3. BGP Add-Path failure
4. IGMP leave processing

Correct Answer: 2. Reverse Path Forwarding failure

Explanation :-

PIM multicast forwarding relies on Reverse Path Forwarding, or RPF, to prevent loops and determine whether an incoming multicast packet arrived through the expected interface toward its source. If the packet arrives on an interface that is not the RPF interface selected by the unicast routing table, the router can drop the packet. This is known as an RPF failure. Engineers troubleshooting multicast forwarding should therefore compare the multicast source’s route in the unicast routing table with the interface on which the packet is arriving. PIM Assert and IGMP mechanisms address different multicast control-plane functions.

Question 217. A network administrator wants to prevent a BGP route from being advertised beyond the immediate receiving autonomous system while still allowing the route to be advertised to that immediate peer. Which BGP community is appropriate?

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

Correct Answer: 4. NO_EXPORT

Explanation :-

The well-known BGP NO_EXPORT community indicates that a route should not be advertised outside the receiving autonomous system or confederation boundary, depending on the applicable BGP environment. This allows a route to be shared with an immediate peer while restricting further external propagation. NO_ADVERTISE is more restrictive because a route carrying that community should not be advertised to any BGP peer. LOCAL_PREF is a path-selection attribute rather than a propagation-control community, while INTERNET is the default community behavior and does not impose the requested restriction.

Question 218. An engineer needs fast detection of forwarding-path failures between two service-provider routers and wants the mechanism to operate independently of a specific routing protocol. Which technology is appropriate?

1. BFD
2. BGP Add-Path
3. Route Target
4. IS-IS CSNP

Correct Answer: 1. BFD

Explanation :-

Bidirectional Forwarding Detection, or BFD, provides rapid detection of failures in the forwarding path between network devices. It is designed to operate independently of the routing protocol and can be associated with protocols such as BGP, OSPF, and IS-IS. This allows routing protocols to react more quickly than they might using their normal protocol timers alone. BGP Add-Path controls the advertisement of multiple paths, Route Targets control VPN route import and export policy, and IS-IS CSNPs support database synchronization. BFD is therefore the appropriate technology for fast, protocol-independent failure detection.

Question 219. A service provider wants to make an IPv6-only customer prefix reachable across an MPLS provider core where the provider core itself continues to use IPv4 infrastructure and MP-BGP. Which technology is specifically designed for IPv6 provider-edge connectivity across an IPv4 MPLS core?

1. 6RD
2. NAT64
3. 6PE
4. GRE

Correct Answer: 3. 6PE

Explanation :-

6PE, or IPv6 Provider Edge, enables IPv6 connectivity across an MPLS network whose core infrastructure uses IPv4. IPv6 routes can be exchanged between provider-edge routers using MP-BGP, while MPLS labels provide transport across the IPv4-based provider core. This allows the provider to support IPv6 services without requiring every core router to run IPv6 routing. 6RD is primarily an IPv6 deployment mechanism over an IPv4 access infrastructure, while NAT64 translates between IPv6 and IPv4 addressing. GRE provides generic tunneling but does not specifically provide the integrated 6PE service model.

Question 220. A BGP router is receiving a large number of prefixes from a customer. The provider wants the BGP session to be automatically protected if the number of received prefixes exceeds an operational threshold. Which feature should be configured?

1. BGP route reflection
2. BGP maximum-prefix
3. BGP MED
4. BGP next-hop-self

Correct Answer: 2. BGP maximum-prefix

Explanation :-

BGP maximum-prefix provides protection against an unexpectedly large number of received routes from a neighbor. The administrator specifies a maximum accepted prefix count, and the router can take configured protective action when that threshold is exceeded. This is especially important for service providers because an accidental customer route leak or routing-policy failure can introduce a very large number of prefixes. Route reflection controls iBGP route distribution, MED influences path selection, and next-hop-self changes the BGP next-hop attribute. None of those features directly provides prefix-count protection for a BGP session.