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

 

Question 81. An IS-IS router on a broadcast network is elected as the Designated Intermediate System. Which function is primarily associated with this role?

1. Establishing BGP route-reflector sessions
2. Generating a pseudonode LSP to represent the broadcast LAN
3. Assigning MPLS VPN Route Targets
4. Selecting the OSPF default route

Correct Answer: 2. Generating a pseudonode LSP to represent the broadcast LAN

Explanation :-

In IS-IS, the Designated Intermediate System (DIS) is elected on broadcast networks to improve the scalability of the link-state database. The DIS generates a pseudonode LSP representing the broadcast segment and the routers attached to it. This reduces the number of individual point-to-point relationships that must be represented in the topology. The IS-IS DIS concept is similar in purpose to the OSPF DR but has important operational differences, including the lack of an OSPF-style BDR. BGP route reflection, MPLS Route Targets, and OSPF default-route selection are unrelated to the IS-IS DIS role.

Question 82. An IS-IS router receives a CSNP that indicates its neighbor is missing an LSP. Which mechanism can be used to request the missing information?

1. BFD
2. BGP UPDATE
3. OSPF LSR packet
4. PSNP

Correct Answer: 4. PSNP

Explanation :-

Partial Sequence Number PDUs (PSNPs) are used by IS-IS routers to request missing LSPs or acknowledge received LSP information. When a router identifies a discrepancy between its local link-state database and the information summarized in a Complete Sequence Number PDU (CSNP), it can use a PSNP to request the missing LSP. CSNPs provide a summary of the LSP database, while PSNPs support synchronization and acknowledgment. BFD provides rapid failure detection, BGP UPDATE messages carry BGP routing information, and OSPF LSR packets belong to a different routing protocol.

Question 83. A provider’s BGP policy must advertise a customer prefix to one upstream provider but prevent the prefix from being advertised to other external autonomous systems. Which mechanism can provide this type of controlled propagation?

1. OSPF Type 3 LSA
2. MPLS PHP
3. BGP community combined with routing policy
4. IS-IS overload bit

Correct Answer: 3. BGP community combined with routing policy

Explanation :-

BGP communities can be attached to routes as policy markers and then interpreted by routing policies to control route propagation. A provider can assign a community to a customer prefix and configure policies on appropriate BGP sessions to permit or restrict advertisement based on that community. The community itself does not automatically enforce the desired behavior unless corresponding routing policy is configured. OSPF Type 3 LSAs are used for inter-area routing, MPLS PHP handles label removal, and the IS-IS overload bit controls transit-path selection. Community-based policy is therefore appropriate for controlled BGP route propagation.

Question 84. A BGP speaker receives several routes to the same destination. After applying policy, the paths have identical Local Preference. Which attribute is generally examined next in the Cisco BGP best-path process?

1. Locally originated path
2. PIM RPF metric
3. MPLS transport label
4. OSPF router priority

Correct Answer: 1. Locally originated path

Explanation :-

Cisco BGP best-path selection evaluates a sequence of attributes. After the highest Local Preference is selected, a path that was locally originated is generally preferred over paths learned from other BGP sources. Local origination can include mechanisms such as network statements, redistribution, or aggregation depending on the specific BGP implementation and route. PIM RPF metrics, MPLS labels, and OSPF router priority are not the next BGP best-path criterion. When troubleshooting unexpected BGP path selection, administrators should evaluate the relevant attributes in their platform’s documented selection sequence rather than relying on a single attribute in isolation.

Question 85. A customer advertises a prefix through two different provider links. The provider wants one link to be preferred for receiving traffic from the Internet. Which customer-side technique can make one advertisement less attractive by manipulating the AS_PATH?

1. Increasing BGP Weight
2. Raising LOCAL_PREF
3. Changing the Route Target
4. AS_PATH prepending

Correct Answer: 4. AS_PATH prepending

Explanation :-

AS_PATH prepending adds additional copies of an autonomous system number to the AS_PATH of an advertised route. This makes that particular advertisement appear to have a longer AS_PATH to downstream BGP speakers. Since AS_PATH length is one factor in BGP best-path selection, the longer path may be less preferred when competing routes otherwise satisfy applicable policies. The technique is commonly used for inbound traffic engineering. Weight and Local Preference primarily influence local or internal path selection, while Route Targets are used for MPLS VPN route import and export policy.

Question 86. An MPLS router has an incoming label that should be removed before the packet is forwarded toward the egress PE. Which forwarding operation represents removal of an MPLS label?

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

Correct Answer: 2. Pop

Explanation :-

An MPLS pop operation removes a label from the top of the MPLS label stack. Penultimate Hop Popping is a specific deployment mechanism where the penultimate router performs this removal for the outer transport label before forwarding toward the egress router. Push adds a label, while swap replaces one label with another. Understanding these operations helps engineers interpret LFIB entries and troubleshoot MPLS forwarding paths. The actual number of labels removed depends on the forwarding operation and service design, but the fundamental operation of removing a label is referred to as pop.

Question 87. Which OSPF mechanism allows an area to summarize multiple specific prefixes into a shorter inter-area advertisement at an ABR?

1. Area range
2. Router priority
3. LSA Type 5 translation
4. DR election

Correct Answer: 1. Area range

Explanation :-

An OSPF ABR can use an area range to summarize multiple more-specific prefixes into a summarized inter-area route. This can reduce the size of routing information advertised between areas and may also reduce the impact of topology changes. The summary is represented through inter-area routing information rather than by combining the underlying links into a single physical network. Router priority influences DR election, Type 5 LSAs describe external routes, and DR election does not perform route summarization. Properly designed area summarization can improve scalability in large service-provider OSPF deployments.

Question 88. An OSPF router needs to advertise a default route into an area only when a specific upstream route exists in its routing table. Which configuration concept addresses this requirement?

1. OSPF DR priority
2. NSSA translation
3. Conditional default-information origination
4. OSPF virtual link

Correct Answer: 3. Conditional default-information origination

Explanation :-

Conditional default-information origination allows an OSPF router to originate a default route only when a specified condition is satisfied, commonly the presence of a particular route. This can prevent a router from advertising itself as a default gateway when the required upstream connectivity is unavailable. The approach is useful in redundant service-provider designs where default-route advertisement should reflect actual upstream reachability. DR priority controls the election of the Designated Router, NSSA translation concerns Type 7 and Type 5 LSAs, and virtual links provide a way to connect areas through an OSPF backbone relationship.

Question 89. A provider uses route reflection and has multiple route-reflector clusters. Which attribute helps a route reflector detect that a route has already passed through its own cluster?

1. NEXT_HOP
2. CLUSTER_LIST
3. MED
4. ORIGIN

Correct Answer: 2. CLUSTER_LIST

Explanation :-

The CLUSTER_LIST attribute records the cluster IDs through which a route has been reflected. When a route reflector receives a route containing its own cluster ID in the CLUSTER_LIST, it can recognize the route as having previously passed through its cluster and reject it to prevent a routing loop. This mechanism is especially important when multiple route reflectors or route-reflector clusters are deployed. ORIGIN identifies how a route entered BGP, NEXT_HOP identifies the forwarding next hop, and MED provides path-selection information between neighboring autonomous systems. CLUSTER_LIST is specifically associated with route-reflector loop prevention.

Question 90. A service provider wants BGP to automatically terminate a session when the number of received prefixes exceeds a configured safety threshold. Which feature should be configured?

1. BGP Add-Path
2. BGP community
3. Route Target
4. Maximum-prefix limit

Correct Answer: 4. Maximum-prefix limit

Explanation :-

The BGP maximum-prefix feature protects a router from unexpectedly receiving an excessive number of routes from a neighbor. An administrator can configure a threshold for the number of accepted prefixes and specify behavior when the limit is exceeded. Depending on the configuration, the BGP session can be reset or otherwise handled according to the configured warning and shutdown behavior. This is especially important on customer and transit sessions because accidental route leaks can introduce very large routing tables. Add-Path, communities, and Route Targets serve different purposes and do not provide this prefix-count protection.

Question 91. A router must carry IPv6 provider-edge traffic through an MPLS core where the core routers run IPv4. Which technology provides IPv6 transport over an IPv4 MPLS backbone?

1. 6PE
2. PIM-SSM
3. LDP targeted session
4. RSVP authentication

Correct Answer: 1. 6PE

Explanation :-

6PE allows IPv6 networks to communicate across an MPLS provider core that can remain IPv4-only at the routing level. Provider-edge routers exchange IPv6 reachability using MP-BGP while MPLS provides the transport through the core. This design avoids requiring every core router to run IPv6 routing protocols. PIM-SSM is a multicast mechanism, targeted LDP provides extended label discovery, and RSVP authentication concerns RSVP signaling security rather than IPv6 transport. 6PE is therefore the appropriate technology when IPv6 edge connectivity must traverse an IPv4 MPLS backbone.

Question 92. Which BGP mechanism can request that a neighboring BGP speaker advertise only a selected subset of routes based on a prefix filter?

1. MED
2. Graceful Restart
3. Outbound Route Filtering
4. Local Preference

Correct Answer: 3. Outbound Route Filtering

Explanation :-

Outbound Route Filtering (ORF) allows a BGP speaker to communicate filtering information to its neighbor so that the neighbor can limit which routes it advertises. This can reduce unnecessary routing updates and improve control over exchanged prefixes. A common example is a prefix-based ORF capability used to coordinate route filtering between BGP peers. MED and Local Preference influence path selection, while Graceful Restart addresses temporary control-plane interruptions. ORF is therefore specifically relevant when one BGP speaker needs to communicate a filtering requirement to influence the routes sent by its neighbor.

Question 93. A PE router receives a VPN route with a valid Route Target but the route is not installed because the corresponding MPLS service label is unavailable. Which plane is primarily involved in providing the label needed for VPN forwarding?

1. PIM control plane
2. OSPF DR election
3. BGP community processing
4. MPLS label distribution and forwarding

Correct Answer: 4. MPLS label distribution and forwarding

Explanation :-

MPLS VPN forwarding depends on labels that identify the appropriate service and transport paths. BGP can distribute VPN reachability information and associated VPN labels, while MPLS forwarding uses the resulting label information to deliver traffic through the provider network. If a VPN route is present but the required label forwarding state is unavailable, troubleshooting should examine the relevant label distribution, LFIB installation, and MPLS forwarding state. PIM and OSPF DR election do not provide VPN service labels. BGP community processing can influence policy but does not itself replace the underlying MPLS forwarding state.

Question 94. Which OSPF LSA type identifies the ASBR that originates external routes when the ASBR is located in another OSPF area?

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

Correct Answer: 1. Type 4 LSA

Explanation :-

A Type 4 ASBR Summary LSA is generated by an ABR to provide reachability information for an ASBR located in another OSPF area. Routers may need this information to determine how to reach the ASBR that originates external routes represented by Type 5 LSAs. Type 1 LSAs describe routers and their links within an area, Type 3 LSAs advertise inter-area networks, and Type 7 LSAs represent external routes inside an NSSA. Therefore, when the question concerns locating an ASBR in another area, Type 4 is the relevant LSA type.

Question 95. An IS-IS Level-1 router learns that a destination is outside its own area. Which type of IS-IS router normally provides the path toward the Level-2 backbone?

1. Another Level-1-only router
2. Level-1-2 router
3. BGP route reflector
4. OSPF ABR

Correct Answer: 2. Level-1-2 router

Explanation :-

An IS-IS Level-1-2 router participates in both Level-1 and Level-2 routing and can provide connectivity between a local Level-1 area and the Level-2 backbone. A Level-1 router generally uses a default route toward an appropriate Level-1-2 router for destinations outside its local area when no more specific route exists. This hierarchical model allows Level-1 routers to avoid maintaining complete inter-area topology information. A Level-1-only router does not provide Level-2 backbone connectivity, while BGP route reflectors and OSPF ABRs belong to different routing mechanisms.

Question 96. Which PIM-SM state represents traffic from a specific multicast source S to a specific multicast group G?

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

Correct Answer: 3. (S,G)

Explanation :-

The (S,G) state in PIM-SM identifies multicast traffic from a particular source S to a particular group G. This source-specific state is used when routers forward traffic along the source tree or otherwise maintain information for that specific source-group combination. The (*,G) state represents shared-tree information for a multicast group without identifying a particular source and is commonly associated with the Rendezvous Point tree. Understanding the difference between (*,G) and (S,G) is essential when troubleshooting PIM-SM forwarding, joins, and source-tree transitions.

Question 97. A service provider wants a BGP router to prefer one external path over another only on that specific router, without advertising the preference to other routers. Which Cisco-specific attribute can be used?

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

Correct Answer: 1. Weight

Explanation :-

Cisco BGP Weight is a local attribute used to influence path selection on the router where it is configured. A higher Weight is preferred, and the value is not advertised to BGP neighbors. This makes Weight useful when an administrator needs a router-specific path preference without affecting BGP best-path selection throughout the autonomous system. LOCAL_PREF, by contrast, is propagated through iBGP and is commonly used for AS-wide outbound path selection. MED and AS_PATH have different scopes and semantics. Weight is therefore appropriate when the preference should remain local to a single Cisco router.

Question 98. An MPLS L3VPN design has two customers using the same IPv4 prefix. Which combination allows the provider to maintain separate VPN routes and control their import into VRFs?

1. MED and Weight
2. BFD and PIM
3. AS_PATH and NEXT_HOP
4. Route Distinguisher and Route Target

Correct Answer: 4. Route Distinguisher and Route Target

Explanation :-

The Route Distinguisher and Route Target perform complementary roles in MPLS L3VPNs. The RD makes otherwise identical customer prefixes unique within the VPNv4 or VPNv6 address family. The RT is carried as an extended community and controls which VRFs import or export the VPN route. This combination allows different customers to use overlapping address space while maintaining separate routing contexts and controlled connectivity. MED, Weight, AS_PATH, and NEXT_HOP are BGP attributes with different functions and do not provide the complete route uniqueness and VRF import/export behavior required by an MPLS L3VPN.

Question 99. A BGP administrator needs to stop an unstable route from repeatedly entering and leaving the routing table and affecting network stability. Which feature is designed specifically to suppress frequently flapping routes?

1. Add-Path
2. ORF
3. Route dampening
4. Maximum-prefix

Correct Answer: 3. Route dampening

Explanation :-

BGP route dampening is designed to reduce the impact of frequently flapping routes. A route accumulates penalty information as it repeatedly changes state, and once configured thresholds are reached, the route can be suppressed temporarily. As the penalty decays over time, the route can eventually become eligible for use again. Add-Path provides multiple path advertisements, ORF provides coordinated outbound filtering, and maximum-prefix protects a session from receiving excessive numbers of routes. Route dampening therefore directly addresses repeated route instability rather than route-count or path-diversity concerns.

Question 100. A service-provider engineer wants to verify whether an MPLS router has learned the expected label binding for a particular FEC, before checking the installed forwarding entry. Which database is most directly relevant?

1. LFIB
2. LIB
3. ARP table
4. PIM database

Correct Answer: 2. LIB

Explanation :-

The Label Information Base (LIB) contains label bindings associated with Forwarding Equivalence Classes learned through MPLS label-distribution mechanisms. It is useful for verifying whether the router has learned the expected label information from its neighbors. The LFIB represents the label forwarding entries actually installed for packet forwarding and is therefore normally checked after confirming the available label bindings. ARP and PIM databases serve different networking functions. Distinguishing the LIB from the LFIB is important when diagnosing cases where a label has been learned but is not appearing in the forwarding plane.