Practise interpreting routing-table output, route selection, administrative distance, metrics, next hops and longest-prefix match.
Start Scenario PracticeA service provider is designing a new MPLS L3VPN service. The customer requires that their VPN traffic be isolated from other customers and that the provider edge routers maintain separate routing tables for each VPN. Which architectural component is essential for this separation?
Explanation: VRF (Virtual Routing and Forwarding) is the essential architectural component that enables a provider edge router to maintain separate, isolated routing tables for each VPN customer. Each VRF instance contains its own routing table, CEF (Cisco Express Forwarding) table, and associated interfaces, ensuring that traffic from one customer is never forwarded using another customer's routing information. This per-VPN isolation is fundamental to MPLS L3VPN services as defined in RFC 4364.
Refer to the exhibit. The router has three LDP neighbors established. A network administrator notices that MPLS labels for the prefix 10.4.4.0/24 are not being advertised from this router to its neighbors, although the prefix is present in the routing table. Which is the most likely cause?
Explanation: LDP only advertises labels for prefixes that are the best path in the routing table (unless label advertisement is configured for all routes). If 10.4.4.0/24 is present but not the best path (e.g., a backup route or a route with a higher administrative distance), LDP will not allocate and advertise a label for it. This matches the symptom of the prefix being in the table but no label being advertised.
A service provider is deploying uRPF on peering edges with multiple upstream providers and asymmetric routing. Which two statements are true about uRPF operation in this scenario? (Choose two.)
Explanation: Option A is correct because loose-mode uRPF only verifies that a route back to the source address exists in the FIB, so if the source prefix is missing from the routing table the packet is dropped even though the return path need not match the incoming interface. Option D is correct because uRPF is supported for both IPv4 (ip verify unicast source reachable-via) and IPv6 (ipv6 verify unicast source reachable-via) on Cisco platforms, making it usable in dual-stack peering designs. Option B is wrong because uRPF depends on Cisco Express Forwarding and the FIB, so CEF must be enabled, not disabled. Option C is wrong because loose mode checks for a specific route to the source in the FIB; a default route alone does not satisfy the check unless it is the matching route. Option E is wrong because strict mode requires the return path to use the same interface the packet arrived on, which breaks in asymmetric routing, so loose mode is preferred there.
In SRv6, which behavior is used for L3VPN decapsulation (removing the outer IPv6 header and SRH, and forwarding the inner IPv4 packet based on the VPN routing table)?
Explanation: End.DT4 is the SRv6 endpoint behavior for decapsulation and table lookup for IPv4 L3VPN. End.DT6 is for IPv6 L3VPN, End.DT2U is for L2VPN.
A service provider deploys uRPF on customer-facing interfaces to prevent IP spoofing. They have a multihomed customer with asymmetric routing. Which uRPF mode should be used to avoid dropping legitimate traffic?
Explanation: Loose mode uRPF checks only that the source address exists in the routing table (FIB), not that the packet arrived on the interface the router would use to reach that source. Because the multihomed customer uses asymmetric routing, return traffic may arrive on a different interface than the one the router would select, so strict mode would drop legitimate packets. Loose mode therefore prevents obvious spoofing (unknown source prefixes) while tolerating asymmetric paths.
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Practice all Show IP Route Output Practice QuestionsPractise interpreting routing-table output, route selection, administrative distance, metrics, next hops and longest-prefix match. These appear throughout the 350-501 and require you to apply your knowledge, not just recall facts.
Cisco doesn't publish an exact breakdown, but scenario-based questions (especially exhibit and command-output formats) make up a significant portion of the 350-501. Practicing each scenario type ensures you're ready for any format.
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