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

 

Question 141.  Which route is normally preferred when the relevant earlier attributes are equal?

1. The iBGP-learned route
2. The eBGP-learned route
3. The route with the higher MED regardless of source
4. The route with the older BGP router ID

Correct Answer: 2. The eBGP-learned route

Explanation :-

Cisco BGP best-path selection considers whether a route was learned through eBGP or iBGP after several earlier attributes have been compared. When the applicable preceding attributes are equal, an eBGP-learned path is normally preferred over an iBGP-learned path. This behavior can influence how traffic exits an autonomous system when multiple otherwise comparable paths are available. The decision is only one stage of the complete BGP best-path algorithm, so attributes such as Weight, LOCAL_PREF, locally originated status, AS_PATH, origin, MED, and other factors can affect the result before this comparison is reached. Troubleshooting should therefore consider the complete selection sequence.

Question 142. A network engineer wants to prevent a BGP customer from advertising prefixes that are not part of the customer’s authorized address space. Which configuration approach is most appropriate?

1. Increase the BGP hold timer
2. Configure a higher MED
3. Enable PIM Assert
4. Apply an inbound prefix list or route policy to the customer session

Correct Answer: 4. Apply an inbound prefix list or route policy to the customer session

Explanation :-

Inbound prefix filtering is a fundamental service-provider technique for controlling which routes are accepted from a customer. A prefix list can explicitly permit authorized prefixes and deny unwanted ones, while a route policy can provide more complex matching and attribute manipulation. Applying the policy inbound on the customer-facing BGP session prevents unauthorized routes from entering the provider’s routing domain. Increasing BGP timers or modifying MED does not provide prefix authorization. PIM Assert is unrelated to BGP route filtering. Providers commonly combine prefix filtering with maximum-prefix protection and other policy controls to reduce the risk of accidental route advertisements or routing-table pollution.

Question 143. An engineer needs to advertise a customer’s IPv6 routes across an MPLS VPN provider network using MP-BGP. Which address family is associated with carrying IPv6 VPN routes?

1. IPv4 unicast
2. IPv4 multicast
3. VPNv6
4. L2VPN only

Correct Answer: 3. VPNv6

Explanation :-

VPNv6 is the Multiprotocol BGP address family used to carry IPv6 VPN routes across an MPLS Layer 3 VPN provider network. Similar to VPNv4 for IPv4 VPN routes, VPNv6 combines IPv6 prefixes with a Route Distinguisher so that overlapping customer addressing can be represented uniquely. Route Targets then control which VRFs import or export those routes. The provider’s PE routers exchange VPNv6 information through MP-BGP while MPLS labels provide the forwarding information needed across the provider core. Understanding the distinction between IPv6 unicast and VPNv6 is important when troubleshooting IPv6 customer routes in an MPLS L3VPN environment.

Question 144. Two OSPF routers on a point-to-point link fail to establish an adjacency. Their interface addresses are reachable, but the OSPF neighbor state remains down. Which configuration should be checked first?

1. OSPF area assignment and interface-level OSPF activation
2. PIM BSR configuration
3. BGP LOCAL_PREF
4. MPLS VPN Route Target

Correct Answer: 1. OSPF area assignment and interface-level OSPF activation

Explanation :-

Before investigating advanced OSPF adjacency states, an engineer should verify that OSPF is actually enabled on both interfaces and that the interfaces belong to the intended OSPF area. IP reachability alone does not guarantee that OSPF Hellos are being exchanged. Other useful checks include OSPF process configuration, interface network type, passive-interface settings, authentication, and Hello/dead timer compatibility. PIM, BGP LOCAL_PREF, and MPLS VPN Route Targets do not determine whether two routers form an OSPF adjacency. A systematic troubleshooting approach starts with interface status and OSPF Hello exchange before progressing to database synchronization and later adjacency states.

Question 145. A provider wants to influence inbound traffic so that remote networks prefer a particular path into its autonomous system. Which technique can increase the AS_PATH length of selected advertisements?

1. Increasing LOCAL_PREF
2. Setting NO_EXPORT
3. Increasing the BGP hold timer
4. AS_PATH prepending

Correct Answer: 4. AS_PATH prepending

Explanation :-

AS_PATH prepending adds one or more copies of the provider’s autonomous-system number to the AS_PATH of selected advertised routes. Because BGP generally prefers a shorter AS_PATH when relevant preceding attributes are equal, this technique can make a path appear less attractive to neighboring autonomous systems. It is commonly used for inbound traffic engineering, although actual remote routing decisions also depend on their local policies and other BGP attributes. LOCAL_PREF primarily influences outbound path selection inside an autonomous system. Therefore, when the objective is to make a particular inbound path less preferred by external networks, AS_PATH prepending is a commonly used policy mechanism.

Question 146. In IS-IS, which packet is used to periodically describe the complete set of LSPs known by a router for database synchronization?

1. PSNP
2. CSNP
3. Hello
4. BGP UPDATE

Correct Answer: 2. CSNP

Explanation :-

A Complete Sequence Number PDU (CSNP) provides a summary of the link-state database by listing the LSPs known to the sending IS-IS router. On broadcast networks, the DIS periodically sends CSNPs to help other routers maintain synchronized databases. If a receiving router determines that it is missing an LSP or has an outdated version, it can use a Partial Sequence Number PDU (PSNP) to request the required information. CSNP and PSNP therefore have complementary roles in IS-IS database synchronization. BGP UPDATE messages and IS-IS Hello packets serve different purposes and do not perform this database-summary function.

Question 147. A provider needs to redistribute selected OSPF routes into BGP while preventing all other OSPF routes from being redistributed. Which mechanism provides granular control?

1. A route policy or route map matching the desired prefixes
2. Increasing the OSPF dead interval
3. Changing the BGP router ID
4. Enabling PIM-SM

Correct Answer: 1. A route policy or route map matching the desired prefixes

Explanation :-

Selective redistribution requires a policy that identifies which routes should be redistributed and which should be rejected. A route policy or route map can match prefixes using prefix lists and then permit only the desired routes. Additional attributes such as route tags, metrics, or communities can also be manipulated depending on the design. Simply changing OSPF timers or the BGP router ID does not control redistribution. In service-provider environments, careful redistribution policy is especially important because uncontrolled redistribution can introduce unexpected routes and routing loops. Prefix filtering and tagging are often combined to make redistribution behavior predictable and easier to troubleshoot.

Question 148. A Cisco router is configured for BGP route reflection. Which attribute helps identify the original BGP speaker that advertised a reflected route?

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

Correct Answer: 3. ORIGINATOR_ID

Explanation :-

The BGP ORIGINATOR_ID attribute is used by route reflection to identify the router that originally originated the reflected route. When a route reflector reflects a route, it can add ORIGINATOR_ID so that subsequent route-reflection processing can recognize the original source and help prevent routing loops. The CLUSTER_LIST provides another loop-prevention mechanism by recording the route-reflector cluster identifiers through which the route has passed. LOCAL_PREF, MED, and Cisco Weight are path-selection attributes rather than route-reflection loop-prevention identifiers. Understanding ORIGINATOR_ID and CLUSTER_LIST is important when troubleshooting unexpected route-reflection behavior in large iBGP topologies.

Question 149. A BGP router is receiving an unexpectedly large number of routes from a peer. Which protection mechanism can be configured to limit the number of accepted prefixes?

1. PIM RPF
2. OSPF LFA
3. MPLS PHP
4. BGP maximum-prefix

Correct Answer: 4. BGP maximum-prefix

Explanation :-

BGP maximum-prefix provides protection by establishing a limit on the number of prefixes accepted from a BGP neighbor. If the received prefix count exceeds the configured threshold, the router can take a configured protective action. This is particularly valuable on customer and transit sessions because an accidental full-table advertisement or route leak could consume substantial router resources. The threshold should be chosen according to the expected route volume and operational requirements. Prefix lists provide filtering based on route characteristics, while maximum-prefix provides a quantity-based safeguard. In production networks, both mechanisms can complement one another as part of a broader BGP protection strategy.

Question 150. A router receives an MPLS packet and removes the top label before forwarding the packet toward the egress PE. Which operation is being performed?

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

Correct Answer: 1. Pop

Explanation :-

An MPLS pop operation removes the top label from the label stack. This can occur as part of normal label processing or through Penultimate Hop Popping (PHP), where the router immediately before the egress LSR removes the outer transport label. Push adds a label to the stack, while swap replaces an incoming label with another outgoing label. Understanding these operations is essential when examining MPLS forwarding entries and troubleshooting an LSP. The exact action depends on the label forwarding information installed in the router. Checking the LFIB can reveal whether the expected label action is pop, swap, or another forwarding operation.

Question 151. Which BGP community prevents a route from being advertised to external autonomous systems while allowing it to remain usable within the receiving autonomous system according to local policy?

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

Correct Answer: 2. NO_EXPORT

Explanation :-

NO_EXPORT is a well-known BGP community used to prevent a route from being advertised outside the receiving autonomous system. The route can still be distributed within that AS according to its routing policy. This makes NO_EXPORT useful for controlling how customer or peer-learned routes propagate beyond a provider’s network. NO_ADVERTISE is more restrictive because it instructs the receiving router not to advertise the route to any BGP peer. The distinction is important when designing community-based routing policies. Administrators should also verify that the community is preserved across the relevant BGP sessions and that local route policies do not remove or override it.

Question 152. A provider wants to reduce traffic loss after a link failure by precomputing a local backup path using Segment Routing. Which technology is specifically designed for fast local protection?

1. BGP Add-Path
2. Route reflection
3. TI-LFA
4. BGP dampening

Correct Answer: 3. TI-LFA

Explanation :-

Topology Independent Loop-Free Alternate (TI-LFA) provides fast local protection in Segment Routing networks. It allows a router to calculate a backup path that can be used rapidly when a protected link or node fails. Segment Routing can encode the required backup path through a segment list, avoiding the need for extensive per-tunnel state in the network. TI-LFA is designed to provide rapid local convergence while maintaining loop-free forwarding during failure recovery. BGP Add-Path addresses path advertisement diversity, route reflection addresses iBGP scalability, and route dampening addresses route instability. None of those mechanisms provides the same local fast-reroute function as TI-LFA.

Question 153. An OSPF router receives a Type 3 LSA from an ABR. What type of information does the Type 3 LSA normally carry?

1. Inter-area network prefixes
2. External routes redistributed from another protocol
3. Router-to-router multicast membership
4. ASBR-specific external metrics only

Correct Answer: 1. Inter-area network prefixes

Explanation :-

OSPF Type 3 Summary LSAs are originated by an Area Border Router (ABR) to advertise network prefixes from one OSPF area into another area. They are used to provide inter-area reachability information. Type 5 LSAs are used for external routes redistributed into the OSPF domain, while Type 7 LSAs are used for external routes within an NSSA. Type 4 LSAs provide information about the reachability of an ASBR. Correctly identifying LSA types is important when troubleshooting why a route is or is not visible across OSPF areas. Examining the LSDB and identifying the originating router and LSA type can help isolate inter-area routing problems.

Question 154. A service provider uses LDP to distribute labels for IGP-reachable prefixes. Which underlying routing information is especially important for establishing a usable MPLS LSP?

1. BGP community values
2. PIM RP information
3. OSPF DR priority only
4. Reachability provided by the IGP

Correct Answer: 4. Reachability provided by the IGP

Explanation :-

LDP commonly relies on an underlying IGP such as OSPF or IS-IS to establish reachability toward network prefixes. The IGP determines the next-hop path, while LDP distributes labels associated with those forwarding destinations. If an IGP route is missing or incorrect, an LDP label binding may not result in a usable end-to-end MPLS forwarding path. This relationship is fundamental to traditional LDP-based MPLS networks. Troubleshooting should therefore examine both the IGP routing table and LDP discovery/session state. A functioning LDP session alone does not guarantee that the expected MPLS LSP is installed and operational.

Question 155. A BGP route reflector receives a route from a non-client and needs to advertise it to its clients. Which statement describes the route-reflection behavior?

1. It must discard the route
2. It can advertise the route to its route-reflector clients, subject to policy
3. It can advertise it only to the original non-client
4. It converts the route into an eBGP route

Correct Answer: 2. It can advertise the route to its route-reflector clients, subject to policy

Explanation :-

Route reflection allows a route reflector to advertise iBGP-learned routes according to specific reflection rules. When a route is received from a non-client iBGP peer, the route reflector can advertise that route to its route-reflector clients. The rules are designed to reduce the need for a full iBGP mesh while maintaining controlled propagation. Route reflection does not convert an iBGP route into an eBGP route, and the route reflector does not automatically discard a route simply because it was learned from a non-client. Routing policy, path selection, and loop-prevention attributes still influence the final behavior.

Question 156. A multicast receiver wants traffic from one specific source for a particular multicast group rather than traffic from all sources using that group. Which multicast model is designed for this requirement?

1. Anycast RP
2. PIM Dense Mode
3. Source-Specific Multicast
4. BGP Add-Path

Correct Answer: 3. Source-Specific Multicast

Explanation :-

Source-Specific Multicast (SSM) allows a receiver to request traffic from a specific source and multicast group, represented as (S,G). This eliminates the need for a shared Rendezvous Point for source selection in the traditional PIM-SM model. SSM commonly uses IGMPv3 for IPv4 receiver membership signaling so that the receiver can identify the desired source. This model is useful for applications where receivers know exactly which source they want to receive. Anycast RP and traditional PIM-SM shared-tree operation address different multicast requirements. BGP Add-Path is unrelated to multicast receiver membership.

Question 157. A provider wants to carry IPv6 customer routes across an MPLS IPv4 core without requiring the core routers to maintain customer IPv6 routes. Which technology is designed for this purpose?

1. PIM-SM
2. OSPFv2
3. BGP Route Reflection
4. 6PE

Correct Answer: 4. 6PE

Explanation :-

6PE allows IPv6 provider edge routers to transport IPv6 traffic across an MPLS core that is based on IPv4 infrastructure. The core does not need to run IPv6 routing for the customer or service traffic because MPLS labels provide the transport across the IPv4 core. IPv6 routes are exchanged between appropriate provider edge routers using MP-BGP, while the core continues using its existing IPv4 routing and MPLS mechanisms. This differs from VPNv6, which is used for IPv6 MPLS Layer 3 VPN services with VRF separation. Understanding 6PE and VPNv6 helps distinguish global IPv6 transport from customer-specific IPv6 VPN services.

Question 158. An IS-IS network administrator needs to request a missing or outdated LSP after comparing the local database with a received database summary. Which PDU is used for this request?

1. PSNP
2. CSNP
3. IIH
4. BGP UPDATE

Correct Answer: 1. PSNP

Explanation :-

A Partial Sequence Number PDU (PSNP) is used by IS-IS routers to acknowledge received LSPs or request specific LSP information that is missing or outdated. A router can compare its database with a Complete Sequence Number PDU and determine that additional information is required. It can then use PSNP mechanisms to request the relevant LSPs. CSNP provides the database summary, while PSNP handles partial acknowledgments and requests. IIH packets establish and maintain IS-IS adjacencies, and BGP UPDATE messages belong to BGP. Understanding CSNP and PSNP interaction is useful when diagnosing IS-IS database synchronization problems.

Question 159. A BGP router receives a route with an unreachable NEXT_HOP address. What is the likely consequence for that route?

1. The route is automatically converted into an OSPF route
2. The route is always installed regardless of reachability
3. The route may not be installed as a usable route because the next hop is unresolved
4. The router automatically changes the next hop to the peer’s address in all cases

Correct Answer: 3. The route may not be installed as a usable route because the next hop is unresolved

Explanation :-

BGP requires recursive reachability to the NEXT_HOP address before a learned route can normally be installed as a usable forwarding route. A BGP route can therefore appear in the BGP table while remaining unusable if the next hop cannot be resolved through the routing table. This is a common troubleshooting issue in provider networks, particularly when eBGP-learned routes are propagated through iBGP without changing the next hop. The next-hop-self feature can address this design issue when appropriate. Engineers should verify both BGP attributes and underlying IGP reachability when a valid-looking BGP route is not installed in the routing table.

Question 160. A provider wants a BGP policy to advertise only a default route to a customer while suppressing all more-specific provider prefixes. Which approach provides direct prefix-level control?

1. Enable BFD on the customer session
2. Use a prefix list or route policy that permits only 0.0.0.0/0
3. Increase the MED on every provider prefix
4. Configure PIM Assert

Correct Answer: 2. Use a prefix list or route policy that permits only 0.0.0.0/0

Explanation :-

A prefix list or route policy can explicitly permit only the default route and deny all other prefixes. For example, an outbound policy can match 0.0.0.0/0 and prevent more-specific routes from being advertised to the customer. This provides deterministic prefix-level control and is preferable when the requirement is to advertise only a specific set of routes. BFD improves failure detection, MED influences BGP path selection, and PIM Assert is a multicast mechanism. In service-provider environments, default-only advertisements are commonly combined with inbound customer prefix filtering and maximum-prefix protection to maintain predictable routing behavior.