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

 

Question 61. An OSPF adjacency remains stuck in the EXSTART state after two routers begin database synchronization. The interface MTU values are different. What is the most likely cause?

1. Duplicate BGP router IDs
2. Incorrect BGP Local Preference
3. Missing MPLS label binding
4. OSPF MTU mismatch

Correct Answer: 4. OSPF MTU mismatch

Explanation :-

During OSPF database exchange, routers negotiate parameters and exchange Database Description packets. A mismatch in interface MTU values can prevent the adjacency from progressing beyond the EXSTART or EXCHANGE stages because a router may reject Database Description packets that advertise an incompatible MTU. The issue should be investigated by comparing the MTU configured on both OSPF interfaces and verifying that any relevant tunnel or encapsulation overhead is accounted for. BGP router IDs, Local Preference, and MPLS label bindings do not directly cause an OSPF adjacency to remain in EXSTART because of an interface MTU mismatch.

Question 62. Which IS-IS mechanism allows a Level-1 router to reach destinations outside its local area when it does not have a more specific route?

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

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

Explanation :-

A Level-1 IS-IS router normally maintains detailed knowledge of destinations within its own area. For destinations outside that area, the router can use a default route toward an attached Level-2 router. This allows the Level-1 router to forward inter-area traffic without maintaining the complete topology of every other IS-IS area. The Level-2 router provides connectivity toward other areas and the backbone. DIS election controls pseudonode behavior on broadcast networks, while CSNPs support database synchronization. LSP fragmentation concerns large link-state databases rather than the normal mechanism for external Level-1 reachability.

Question 63. A provider wants to preserve an existing BGP community when applying a route policy and add another community at the same time. Which community action should be used?

1. Additive
2. Replace
3. Delete
4. Suppress

Correct Answer: 1. Additive

Explanation :-

The additive community action allows a new BGP community to be added without replacing the communities already associated with the route. This is useful when a provider needs to apply an additional routing policy while preserving previously assigned community information. Without the additive behavior, depending on the configuration and platform syntax, setting communities can replace the existing community set. Community-based policies are commonly used for controlling route propagation, traffic engineering, and customer-specific handling. Therefore, additive behavior is appropriate when the objective is to retain existing communities while appending another value.

Question 64. A PE router receives a VPNv4 route with an RD that makes the prefix unique, but the route is not imported into the expected VRF. Which configuration should be checked first?

1. BGP Weight
2. MPLS PHP configuration
3. VRF import Route Target
4. OSPF router priority

Correct Answer: 3. VRF import Route Target

Explanation :-

The Route Distinguisher creates uniqueness for VPNv4 prefixes, but it does not determine which VRF receives the route. VRF import Route Targets control whether a VPN route is imported into a particular VRF. If a PE receives the route but the expected VRF does not contain it, the administrator should compare the route’s Route Target extended communities with the VRF’s configured import RT values. BGP Weight affects local BGP path selection, PHP concerns MPLS label handling, and OSPF router priority applies to DR election. The import RT is therefore the key configuration to verify.

Question 65. A BGP administrator wants to advertise only selected routes from a customer-facing router to an upstream provider. Which configuration mechanism provides prefix-based outbound filtering?

1. MED
2. Prefix list
3. BFD
4. Route Distinguisher

Correct Answer: 2. Prefix list

Explanation :-

A prefix list provides explicit prefix-based filtering and can be applied through routing policy mechanisms to control which routes are advertised or accepted. For an outbound BGP policy, a prefix list can permit only approved customer prefixes while denying all other routes. This is a common protection against accidental route leaks and unintended advertisements. MED is a path-selection attribute, BFD is a failure-detection mechanism, and the Route Distinguisher provides VPN route uniqueness. Prefix lists can also be combined with route maps or route policies to implement more sophisticated filtering and attribute modification.

Question 66. Which BGP community prevents a route from being advertised outside the local autonomous system while still allowing it to be advertised to other iBGP speakers?

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

Correct Answer: 4. NO_EXPORT

Explanation :-

The well-known NO_EXPORT community instructs BGP speakers not to advertise the associated route outside the local autonomous system or applicable confederation boundary. The route can still be propagated internally through iBGP as permitted by the local routing policy. NO_ADVERTISE is more restrictive because it prevents the route from being advertised to any BGP peer. INTERNET is not a restriction mechanism, while BLACKHOLE is commonly used in specialized mitigation policies rather than providing the standard NO_EXPORT behavior. Understanding the distinction between NO_EXPORT and NO_ADVERTISE is important when designing controlled route propagation.

Question 67. A service-provider router has an MPLS label binding in the LIB but does not forward labeled packets according to that binding. Which table should be examined to verify the actual forwarding action?

1. ARP table
2. BGP RIB
3. LFIB
4. DNS cache

Correct Answer: 3. LFIB

Explanation :-

The Label Information Base (LIB) contains label bindings learned from label distribution mechanisms, but it is not the table that directly performs packet forwarding. The Label Forwarding Information Base (LFIB) contains the operational label forwarding entries installed for use by the forwarding plane. If a label binding exists in the LIB but forwarding behavior is incorrect, the LFIB should be inspected to determine whether the expected swap, push, or pop action has been installed. ARP, BGP RIB information, and DNS data do not directly represent MPLS label forwarding operations. This distinction is important during MPLS troubleshooting.

Question 68. Which BGP feature allows a router to advertise multiple paths for a prefix to improve path diversity and reduce dependence on a single selected path?

1. BGP Add-Path
2. Route dampening
3. MED
4. BGP Weight

Correct Answer: 1. BGP Add-Path

Explanation :-

BGP Add-Path enables a BGP speaker to advertise multiple paths for the same prefix rather than advertising only one selected best path. This can improve path visibility and provide downstream routers with additional alternatives. It is particularly useful in service-provider environments where hiding alternate paths can contribute to suboptimal routing or slower recovery. Route dampening is intended to control unstable routes, MED influences path selection between neighboring autonomous systems, and Weight is a Cisco-local attribute. Add-Path therefore directly addresses the requirement for multiple path advertisements and greater path diversity.

Question 69. An MPLS L3VPN packet reaches the PE router but the PE cannot identify the correct customer VRF from the VPN route information. Which information is primarily associated with identifying the VPN route’s unique prefix?

1. BGP MED
2. Local Preference
3. PIM RP address
4. Route Distinguisher

Correct Answer: 4. Route Distinguisher

Explanation :-

The Route Distinguisher is used to make customer prefixes unique within the VPNv4 or VPNv6 address family. This is essential when multiple customers use overlapping IPv4 or IPv6 address space. The RD is combined with the customer prefix to form a VPN-specific route identifier. Route Targets then determine the import and export relationships between VPN routes and VRFs. MED and Local Preference influence BGP path selection, while a PIM RP address is related to multicast routing. Understanding the separate roles of RD and RT is essential when troubleshooting MPLS L3VPN route distribution.

Question 70. Which OSPF LSA provides information about networks reachable through another OSPF area?

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

Correct Answer: 2. Type 3

Explanation :-

Type 3 Summary LSAs are generated by OSPF Area Border Routers to advertise networks from one area into another. They provide inter-area reachability information without requiring routers in the receiving area to know the detailed internal topology of the originating area. Type 1 LSAs describe individual routers and their links, Type 5 LSAs advertise external routes, and Type 7 LSAs represent external routes within an NSSA. When troubleshooting inter-area reachability, examining Type 3 LSAs and the ABR’s summarization or filtering policy is therefore important.

Question 71. A BGP route reflector receives a route from a client and reflects it to another client. Which attribute identifies the original BGP speaker to help prevent reflection loops?

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

Correct Answer: 3. ORIGINATOR_ID

Explanation :-

The ORIGINATOR_ID attribute identifies the BGP router ID of the router that originally originated the route into the route-reflector environment. Route reflectors add or preserve this information when reflecting routes. If a router receives a reflected route with an ORIGINATOR_ID corresponding to itself, it can recognize a potential reflection loop and reject the route. CLUSTER_LIST provides another important loop-prevention mechanism between route-reflector clusters. MED, NEXT_HOP, and LOCAL_PREF serve different purposes in BGP path selection and forwarding. ORIGINATOR_ID is specifically associated with identifying the original BGP originator.

Question 72. Which mechanism is commonly used with BGP to rapidly detect a failed peer without waiting for relatively long BGP hold timers?

1. BFD
2. MED
3. Route Target
4. AS_PATH prepending

Correct Answer: 1. BFD

Explanation :-

Bidirectional Forwarding Detection (BFD) provides rapid detection of forwarding-path failures by exchanging lightweight control packets at short intervals. BGP can use BFD to detect a peer failure much faster than relying solely on its standard Keepalive and Hold Timer mechanism. When BFD detects the failure, the associated routing protocol session can react quickly, improving convergence. MED and AS_PATH prepending influence BGP route selection or traffic engineering, while Route Targets control VPN route import and export. BFD is therefore particularly useful in service-provider networks where fast failure detection and convergence are important.

Question 73. A service provider wants to prevent a customer from accidentally advertising the provider’s entire Internet routing table back toward the provider. Which policy approach is most appropriate?

1. Increase the MED value
2. Apply an outbound prefix filter
3. Enable PIM-SM
4. Change the MPLS RD

Correct Answer: 2. Apply an outbound prefix filter

Explanation :-

An outbound prefix filter can restrict the routes a customer-facing BGP session is permitted to advertise toward the provider. This protects against accidental route leaks and ensures that only authorized customer prefixes are announced. Prefix lists or equivalent policy mechanisms can explicitly permit expected prefixes and deny everything else. MED does not provide route advertisement filtering, PIM-SM is a multicast routing protocol, and changing an MPLS Route Distinguisher does not control ordinary customer-to-provider BGP advertisements. Proper filtering is therefore a key operational safeguard at service-provider peering boundaries.

Question 74. Which MPLS label operation adds a new label to the top of an existing label stack?

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

Correct Answer: 4. Push

Explanation :-

A push operation adds a new MPLS label to the packet’s existing label stack. This is commonly required when an additional label is needed for services such as MPLS VPN forwarding, where a packet can carry both a transport label and a VPN service label. A swap operation replaces an existing label, while pop removes a label. Penultimate Hop Popping is a specific mechanism in which the penultimate router removes the outer transport label before forwarding toward the egress. Recognizing push, swap, and pop operations is fundamental when interpreting MPLS forwarding behavior and label stacks.

Question 75. In Segment Routing, which SID type identifies a specific adjacency between two directly connected routers?

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

Correct Answer: 1. Adjacency SID

Explanation :-

An Adjacency SID identifies a specific adjacency or link from one Segment Routing router toward a directly connected neighbor. By including an Adjacency SID in a segment list, traffic can be directed over a particular link rather than relying solely on shortest-path behavior toward a destination node. A Node SID represents reachability toward a specific node, while a Binding SID represents an instantiated SR policy or segment list. An Anycast SID can represent a group of nodes sharing an anycast function. Adjacency SIDs are therefore especially useful for explicit path control and traffic engineering.

Question 76. A Segment Routing policy contains several candidate paths. Which characteristic is commonly used to determine which valid candidate path is preferred?

1. OSPF router priority
2. MPLS label value
3. Candidate-path preference
4. BGP MED only

Correct Answer: 3. Candidate-path preference

Explanation :-

Segment Routing policies can contain multiple candidate paths, allowing different path definitions or sources to be available for a policy. Candidate-path preference is used to determine the preferred valid candidate among available choices according to the applicable SR policy selection rules. A higher preference can be selected when the relevant candidates are otherwise eligible, depending on implementation and policy semantics. OSPF router priority relates primarily to DR election, MPLS label values are forwarding identifiers, and BGP MED is a BGP path-selection attribute. Candidate-path preference is therefore central to selecting among valid SR policy alternatives.

Question 77. Which multicast protocol mechanism allows routers in a PIM-SM domain to learn candidate Rendezvous Points and distribute RP information?

1. BFD
2. LDP
3. BGP Add-Path
4. Bootstrap Router mechanism

Correct Answer: 4. Bootstrap Router mechanism

Explanation :-

The PIM Bootstrap Router (BSR) mechanism distributes information about available candidate Rendezvous Points within a PIM-SM domain. A BSR is elected from candidate BSRs and distributes RP information so that routers can determine the appropriate RP for multicast groups. This provides a dynamic method for distributing RP information without requiring every router to be manually configured with identical static RP entries. BFD is a failure-detection mechanism, LDP distributes MPLS labels, and BGP Add-Path controls multiple BGP path advertisements. The BSR mechanism is therefore directly associated with dynamic PIM-SM RP discovery and distribution.

Question 78. A provider needs to carry IPv6 VPN routes across an MPLS backbone using MP-BGP. Which address family is used for this purpose?

1. IPv4 unicast
2. VPNv6
3. IPv4 multicast
4. EVPN only

Correct Answer: 2. VPNv6

Explanation :-

VPNv6 is the MP-BGP address family used to carry IPv6 VPN routes across an MPLS provider network. Similar to VPNv4 for IPv4 VPN routes, VPNv6 combines IPv6 prefixes with Route Distinguishers to provide uniqueness and uses Route Targets to control VPN route import and export. This allows multiple customer VPNs to use overlapping IPv6 address spaces while maintaining separate routing contexts. IPv4 unicast does not represent IPv6 VPN routes, IPv4 multicast serves a different purpose, and EVPN is a separate control-plane technology with different route types and service models.

Question 79. A PIM-SM router receives multicast traffic from an interface that is not the expected RPF interface. What action does the router normally take?

1. Drop the packet
2. Convert the packet to unicast
3. Increase the BGP Local Preference
4. Install an MPLS VPN label

Correct Answer: 1. Drop the packet

Explanation :-

PIM routers use the Reverse Path Forwarding check to verify that multicast traffic arrives through the interface expected to provide the shortest or preferred unicast path toward the source. If a packet arrives on an interface that fails the RPF check, the router normally drops the multicast packet rather than forwarding it further. This prevents multicast forwarding loops and duplicate traffic. Troubleshooting an RPF failure should therefore include examining the unicast routing table, source address, RPF interface, and PIM neighbor relationships. BGP attributes and MPLS VPN labels do not directly resolve an invalid multicast RPF interface.

Question 80. Which BGP attribute is normally preferred when comparing multiple otherwise valid paths and is used to influence outbound path selection within a Cisco autonomous system?

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

Correct Answer: 3. LOCAL_PREF

Explanation :-

LOCAL_PREF is a key BGP attribute used to influence outbound path selection within an autonomous system. Cisco BGP generally prefers the path with the higher Local Preference value when comparing eligible routes. Because LOCAL_PREF is propagated through iBGP, it can provide consistent exit-path policy across the autonomous system. AS_PATH length is another important best-path criterion, while MED is primarily used to communicate preferred entry points to a neighboring autonomous system. Communities themselves are normally policy markers rather than direct best-path values. LOCAL_PREF is therefore the standard mechanism for controlling preferred outbound exits.