300-420 Exam Dumps : Designing Cisco Enterprise Networks

Ethernet Local Management Interface is used between the customer edge and provider edge to communicate service status information for Ethernet services. Under MEF Ethernet service operations, E-LMI provides the CE with information about Ethernet Virtual Connection status, including whether a configured EVC is available or unavailable. This allows the customer device to react to a provider-side service condition without relying only on physical link state. The CE-to-PE link can remain physically up even while the provider EVC is down; E-LMI closes that operational visibility gap by reporting the EVC state to the customer edge. It is not a routing protocol and does not broadcast multicast routes from the CE to the PE. It also does not broadcast to all subnets when an EVC is added. The key function defined by the MEF process is notifying the CE of EVC availability state and related service information. Reference topics: Metro Ethernet, E-LMI, Ethernet Virtual Connection, CE-to-PE signaling, MEF service operations.

The design must enable IPv6 multi-topology behavior at the appropriate edge routers and move metric handling toward transition support where the current IS-IS network still uses narrow metrics. Multi-topology IS-IS is important during IPv4-to-IPv6 migration because IPv4 and IPv6 reachability do not always exist on identical links at every stage of the migration. If IPv6 follows the IPv4 topology when some devices or paths are not IPv6-ready, traffic can be blackholed. Multi-topology allows independent IPv4 and IPv6 SPF calculations, which prevents IPv6 traffic from being forwarded through IPv4-only portions of the network. The metric-style transition setting is used when migrating from narrow to wide metrics, allowing interoperability while routers are upgraded and the design scales. Because the requirement says IPv6 areas will grow and the current network uses narrow metrics, the selected edge devices must support the IPv6 topology and metric transition behavior shown in the exhibit. Reference topics: IS-IS IPv6, multi-topology IS-IS, narrow metrics, wide metric transition, IPv6 migration, blackhole prevention.

Nonstop Routing is the correct solution when the upstream router does not understand graceful restart messaging. Cisco NSF and graceful restart depend on helper behavior from neighboring routers. During a supervisor switchover, the restarting device asks neighbors to preserve forwarding and adjacency state while the control plane recovers. If the neighbor does not support or understand the graceful restart signaling, NSF cannot deliver the intended benefit and route recomputation may still occur. NSR is different because it synchronizes routing protocol state between the active and standby supervisor internally, allowing the switch to preserve routing operation during stateful switchover without requiring graceful restart support from the neighbor. Remote LFA FRR protects against data-plane failures by precomputing repair paths, but it does not address supervisor switchover route recomputation. Aggressive IS-IS timers may make failure detection faster, but they increase control-plane churn and do not solve the lack of graceful-restart helper support. Therefore, the Catalyst switch should use NSR for this design. Reference topics: IS-IS high availability, NSR, NSF, graceful restart helper support, stateful switchover.