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

 

Question 181. A provider is troubleshooting an MPLS LDP network. The LDP session between two routers is down even though their loopback addresses are reachable. Which protocol transport should be verified?

1. UDP port 520
2. TCP port 179
3. UDP port 500
4. TCP port 646

Correct Answer: 4. TCP port 646

Explanation :-

LDP uses TCP port 646 for reliable session establishment and maintenance between LDP peers. LDP discovery uses UDP, but the actual LDP session operates over TCP. Therefore, when an LDP session fails despite basic IP reachability, the engineer should verify TCP connectivity to port 646, along with router IDs, targeted versus directly connected discovery, access-control policies, and LDP configuration. TCP port 179 belongs to BGP, while the other listed ports are unrelated to LDP session establishment. Checking both LDP discovery and TCP session state helps distinguish a discovery problem from a session-establishment problem.

Question 182. In an IS-IS broadcast network, which router is responsible for generating the pseudonode LSP representing the broadcast segment?

1. The router with the lowest system ID
2. The Designated IS (DIS)
3. Every Level-1 router independently
4. The BGP route reflector

Correct Answer: 2. The Designated IS (DIS)

Explanation :-

On a broadcast LAN, IS-IS elects a Designated Intermediate System (DIS) to represent the multiaccess segment through a pseudonode. The DIS generates a pseudonode LSP that describes the routers connected to that LAN. This reduces the need for every router to establish a full set of point-to-point-style topology relationships in the link-state representation. Unlike OSPF, IS-IS does not elect a backup DIS in the same manner as the OSPF DR/BDR model. DIS election is therefore an important part of understanding IS-IS operation on broadcast networks and troubleshooting database information associated with a shared LAN.

Question 183. A BGP router receives a route with the NO_ADVERTISE community. According to the standard meaning of this well-known community, what should the receiving router do?

1. It should not advertise the route to any BGP peer
2. It should advertise the route only to eBGP peers
3. It should remove the community and advertise the route normally
4. It should increase the route’s LOCAL_PREF

Correct Answer: 1. It should not advertise the route to any BGP peer

Explanation :-

NO_ADVERTISE is a well-known BGP community that instructs the receiving BGP speaker not to advertise the associated route to other BGP peers. This is more restrictive than NO_EXPORT, which permits distribution within the receiving autonomous system while preventing advertisement outside that AS. Community handling can still be affected by local policy, so operators should verify how their implementation preserves or modifies communities. NO_ADVERTISE is useful when a route should remain local to the receiving BGP speaker rather than being propagated further. It does not directly modify LOCAL_PREF or determine the route’s best-path status.

Question 184. A provider wants to distribute IPv4 customer VPN routes between PE routers using MP-BGP. Which address family is normally used?

1. IPv4 multicast
2. IPv6 unicast
3. VPNv4
4. L2VPN only

Correct Answer: 3. VPNv4

Explanation :-

VPNv4 is the MP-BGP address family used to carry IPv4 MPLS Layer 3 VPN routes between provider edge routers. It combines IPv4 prefixes with Route Distinguishers so that overlapping customer address spaces can coexist in the provider’s VPN routing table. Route Targets are then used to control which VRFs import or export those routes. MPLS labels provide the forwarding information needed to deliver traffic across the provider network. IPv4 unicast BGP does not by itself provide the required VPN separation and RD/RT semantics. Understanding VPNv4 is therefore essential when troubleshooting IPv4 MPLS L3VPN route distribution.

Question 185. An OSPF router is configured as an ABR and summarizes several internal prefixes toward another area. Which mechanism can be used to perform this summarization?

1. BGP community
2. Area range
3. PIM Assert
4. MPLS PHP

Correct Answer: 2. Area range

Explanation :-

OSPF ABRs can summarize networks from one area when advertising them into another area using an area-range configuration. Summarization reduces the number of individual prefixes propagated between areas and can improve scalability. It can also provide a more stable representation of internal address space when individual component prefixes change. OSPF summarization is performed by the ABR rather than by an ordinary internal router. BGP communities, PIM Assert, and MPLS PHP are unrelated mechanisms. When designing summarization, engineers should ensure that the summary accurately represents the underlying address space and understand the behavior when component routes disappear.

Question 186. A BGP session between two routers is configured using loopback addresses rather than directly connected interface addresses. Which configuration is commonly required when the peers are not directly connected?

1. PIM sparse mode
2. OSPF stub area
3. MPLS PHP
4. ebgp-multihop

Correct Answer: 4. ebgp-multihop

Explanation :-

When eBGP peers use loopback addresses and are separated by multiple Layer 3 hops, the default eBGP TTL behavior may prevent the session from establishing. The ebgp-multihop feature allows the BGP session to use a larger TTL value suitable for the required path. The underlying routing must also provide reachability between the loopbacks, and the correct update-source configuration is commonly required when loopbacks are used as the BGP source addresses. This differs from iBGP, where the default TTL behavior and multihop considerations are different. Troubleshooting should therefore verify both routing reachability and BGP transport settings.

Question 187. A service provider needs to ensure that traffic uses a particular link in an SR-MPLS network rather than simply following the shortest path to a destination node. Which SID type provides link-specific control?

1. Node SID
2. Prefix SID only
3. Adjacency SID
4. Route Target

Correct Answer: 3. Adjacency SID

Explanation :-

An Adjacency SID identifies a particular adjacency or link associated with a Segment Routing node. Including an Adjacency SID in a segment list allows traffic engineering to specify that a particular link should be traversed. A Node SID generally represents reachability to a node and follows the topology’s shortest path toward that node. This distinction provides Segment Routing with both scalable node-level forwarding and more explicit link-level path control. Route Targets belong to MPLS VPN policy and are not Segment Routing identifiers. Adjacency SIDs are therefore useful when an SR policy needs to constrain traffic to a particular link.

Question 188. A BGP administrator wants to prevent a route learned from one provider from being propagated to another external provider while still allowing internal routers to use it. Which community is appropriate?

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

Correct Answer: 1. NO_EXPORT

Explanation :-

NO_EXPORT is designed for situations where a route should remain within the receiving autonomous system and should not be advertised to external autonomous systems. Internal BGP routers can continue to use and propagate the route according to normal iBGP and local-policy rules. NO_ADVERTISE is stricter because it prevents advertisement to any BGP peer. ORIGINATOR_ID is a route-reflection loop-prevention attribute and has no equivalent route-containment function. Proper use of NO_EXPORT can therefore help providers control route propagation between external peers while retaining the route for internal routing decisions.

Question 189. An OSPF router in an NSSA receives an external route redistributed by a local router. Which LSA type represents that external route inside the NSSA before any ABR translation?

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

Correct Answer: 4. Type 7

Explanation :-

External routes redistributed into an OSPF Not-So-Stubby Area are represented using Type 7 LSAs. NSSAs allow controlled external route injection while retaining restrictions on normal Type 5 flooding. An NSSA ABR can translate eligible Type 7 LSAs into Type 5 LSAs so the external routes can be advertised into the wider OSPF domain. Type 3 LSAs are used for inter-area network summaries, Type 4 LSAs identify reachability to an ASBR, and Type 5 LSAs represent normal external routes outside the NSSA context. Troubleshooting NSSA redistribution therefore requires checking both Type 7 origination and ABR translation.

Question 190. A provider wants to reduce the amount of IPv4 routing information required on the core while carrying IPv6 traffic between PE routers. Which technology can accomplish this using an IPv4 MPLS core?

1. VPNv4
2. 6PE
3. PIM-SSM
4. OSPFv3 only

Correct Answer: 2. 6PE

Explanation :-

6PE allows IPv6 traffic to traverse an MPLS core that uses IPv4 infrastructure. Provider edge routers exchange IPv6 reachability information using MP-BGP, while the core routers can continue operating with IPv4 routing and MPLS. This allows service providers to introduce IPv6 connectivity without requiring every core router to maintain IPv6 routing information. VPNv4 is intended for IPv4 MPLS Layer 3 VPN routes, while PIM-SSM is a multicast technology. OSPFv3 provides IPv6 routing but does not itself provide the 6PE architecture. 6PE is therefore specifically suited to transporting IPv6 across an IPv4 MPLS provider core.

Question 191. A BGP route is visible in the BGP table but is not selected as the best path because the next-hop address is unreachable. What fundamental requirement is missing?

1. A valid PIM RP
2. A matching Route Target
3. Reachability to the BGP next-hop address
4. An OSPF DR election

Correct Answer: 3. Reachability to the BGP next-hop address

Explanation :-

BGP routes require recursive next-hop resolution before they can normally be installed as usable forwarding routes. A route can therefore appear in the BGP table while remaining unusable if the next-hop address cannot be resolved through the routing table. This is common when an eBGP-learned route is propagated through iBGP while retaining the original external next hop. A provider can often address this design by using next-hop-self where appropriate. Troubleshooting should verify the IGP route to the next-hop address, interface reachability, routing-table recursion, and any route policies that may affect next-hop processing.

Question 192. In PIM-SM, what does (*,G) state represent?

1. A shared-tree state for multicast group G without a specific source
2. A source-specific state for source S and group G
3. An MPLS VPN route
4. A BGP multicast path

Correct Answer: 1. A shared-tree state for multicast group G without a specific source

Explanation :-

The (*,G) notation in PIM-SM represents shared-tree state for multicast group G without identifying a specific source. This state is associated with the multicast distribution tree rooted at the Rendezvous Point in traditional PIM-SM operation. Once traffic is identified from a specific source, routers can build source-specific (S,G) state and potentially switch to a shortest-path tree. Understanding the distinction between (*,G) and (S,G) is essential when analyzing multicast routing tables and troubleshooting PIM forwarding. SSM generally uses source-specific membership and does not depend on the traditional shared-tree model.

Question 193. Which BGP attribute is normally propagated through an autonomous system to communicate the preferred outbound exit point to internal BGP routers?

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

Correct Answer: 2. LOCAL_PREF

Explanation :-

LOCAL_PREF communicates an autonomous system’s preferred exit point for outbound traffic and is propagated through iBGP. A higher LOCAL_PREF is preferred during BGP best-path selection. This makes it a fundamental attribute for provider and enterprise traffic engineering when multiple external paths are available. AS_PATH describes the autonomous systems traversed by a route, while MED can provide information about preferred entry points to a neighboring AS under applicable conditions. NEXT_HOP identifies the address used to reach the route and is essential for recursive resolution, but it does not express the same outbound preference policy as LOCAL_PREF.

Question 194. A BGP administrator wants to advertise only selected customer prefixes to an upstream provider. Which outbound mechanism is most appropriate?

1. BFD
2. PIM Assert
3. OSPF virtual link
4. Prefix list combined with a route policy

Correct Answer: 4. Prefix list combined with a route policy

Explanation :-

A prefix list combined with a route policy provides granular control over which routes are advertised to an upstream BGP provider. The prefix list identifies the permitted or denied prefixes, while the route policy applies the filtering and can also manipulate attributes when required. This is commonly used to prevent accidental advertisement of internal, private, or unauthorized routes. BFD handles failure detection, PIM Assert addresses multicast forwarding, and OSPF virtual links address backbone connectivity. Outbound route filtering is especially important at provider boundaries because it directly controls the routing information exposed to external autonomous systems.

Question 195. An IS-IS router is configured with authentication on its routing packets. What is the primary purpose of this configuration?

1. To encrypt all user traffic
2. To create MPLS labels
3. To validate authorized IS-IS control-plane packets
4. To change BGP LOCAL_PREF

Correct Answer: 3. To validate authorized IS-IS control-plane packets

Explanation :-

IS-IS authentication protects the routing control plane by allowing routers to validate that received IS-IS packets contain the expected authentication information. This helps prevent unauthorized or malformed routing information from being accepted into the link-state database. Authentication does not encrypt customer traffic or create MPLS labels. The exact authentication configuration depends on the IS-IS implementation and packet types being protected. When troubleshooting an authenticated adjacency, engineers should verify that both routers use compatible authentication settings, keys, and applicable interface or area configuration. Authentication failures can prevent adjacencies from forming or cause existing relationships to fail.

Question 196. A provider uses PIM-SM and wants multiple routers to share responsibility for the same multicast Rendezvous Point address for resilience. Which design is commonly used?

1. BGP Add-Path
2. MPLS PHP
3. Anycast RP
4. OSPF virtual link

Correct Answer: 3. Anycast RP

Explanation :-

Anycast RP allows multiple Rendezvous Point routers to use the same logical RP address, improving resilience and distribution of multicast control-plane responsibilities. Multicast sources and receivers can reach an appropriate RP instance based on the unicast routing topology. MSDP is commonly used between Anycast RP routers to exchange source information in traditional PIM-SM designs. BGP Add-Path, MPLS PHP, and OSPF virtual links solve unrelated networking problems. Anycast RP is therefore an important multicast availability technique when a provider wants to avoid relying on a single physical RP router.

Question 197. A BGP administrator wants to identify whether a route has passed through a particular route-reflector cluster. Which attribute should be inspected?

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

Correct Answer: 4. CLUSTER_LIST

Explanation :-

The BGP CLUSTER_LIST records the cluster IDs of route reflectors through which a reflected route has passed. Route reflectors use this attribute as a loop-prevention mechanism. If a route reflector receives a route containing its own cluster ID, it can reject the route to prevent reflection loops. ORIGINATOR_ID provides complementary information about the original route originator. Weight, LOCAL_PREF, and MED are path-selection attributes rather than route-reflector cluster tracking mechanisms. Inspecting CLUSTER_LIST can therefore be particularly useful when troubleshooting unexpected route propagation or loops in a topology containing multiple route-reflector clusters.

Question 198. A service provider has an MPLS L3VPN where the customer prefix is correctly present in the local VRF and the remote PE has the corresponding VPN route. Which additional information is required for the remote PE to identify the customer VRF when traffic arrives?

1. An MPLS VPN label
2. A PIM Assert message
3. An OSPF Type 4 LSA
4. A BGP MED value

Correct Answer: 1. An MPLS VPN label

Explanation :-

In an MPLS L3VPN, the VPN label carried toward the remote PE identifies the VPN or VRF context associated with the packet. The outer transport label is used to move the packet across the MPLS core toward the remote PE, while the VPN label allows the receiving PE to select the appropriate customer forwarding context. The control plane distributes this information through mechanisms associated with MP-BGP and label signaling. A BGP MED value, PIM Assert, or OSPF Type 4 LSA does not identify the customer VRF for MPLS VPN forwarding. Troubleshooting should therefore examine both transport and VPN label operations.

Question 199. A service provider observes that an OSPF neighbor remains in EXSTART and the two routers have different interface MTU values. What is the likely effect?

1. The routers automatically become DR and BDR
2. The routers form a BGP session instead
3. The adjacency may fail to progress because of the MTU mismatch
4. The routers disable OSPF authentication

Correct Answer: 3. The adjacency may fail to progress because of the MTU mismatch

Explanation :-

An MTU mismatch can prevent OSPF neighbors from progressing beyond the EXSTART or EXCHANGE stages because Database Description packets are exchanged with MTU information. If one router advertises an interface MTU that the other router cannot accommodate, the adjacency may repeatedly fail to synchronize databases. Troubleshooting should compare interface MTU values on both ends and verify other OSPF parameters such as area, authentication, network type, and timers. The issue is unrelated to BGP, DR/BDR election by itself, or authentication changes. Correcting the MTU mismatch can allow database synchronization and normal FULL adjacency establishment.

Question 200. A network engineer wants to verify the actual MPLS forwarding action for an incoming label on a Cisco router. Which forwarding structure should be examined?

1. LFIB
2. BGP community table
3. OSPF neighbor table
4. PIM multicast table

Correct Answer: 1. LFIB

Explanation :-

The MPLS Label Forwarding Information Base (LFIB) contains the forwarding actions associated with labels, such as swap, push, or pop, along with the outgoing interface and next-hop information. It therefore provides the most direct view of how the router will process an incoming MPLS label in the forwarding plane. The LIB represents label bindings in the control plane, while BGP, OSPF, and PIM tables contain routing or multicast information for different functions. During MPLS troubleshooting, comparing LIB and LFIB entries can reveal whether a learned label binding has been successfully installed into the forwarding plane.