300-420 Exam Dumps : Designing Cisco Enterprise Networks

BIDIR-PIM is the correct multicast solution for interactive many-to-many communication with many sources when source trees must not be used. Bidirectional PIM is specifically designed for applications where receivers can also be senders and where the number of sources can grow without creating per-source multicast state throughout the network. Instead of building shortest-path trees for each source, BIDIR-PIM uses a shared tree rooted at the rendezvous point and forwards traffic bidirectionally along that tree. This reduces multicast routing-table growth and control-plane churn in environments with many active sources. PIM dense mode is not appropriate because it floods and prunes traffic and is inefficient at scale. Any-source multicast with PIM-SM may create source trees, which violates the requirement. MSDP is used to exchange source information between PIM-SM domains and is not itself the forwarding mode for this campus or WAN multicast design. Reference topics: BIDIR-PIM, many-to-many multicast, shared tree, multicast source scaling, PIM design.

BGP outbound route filtering is the correct solution because the enterprise wants control over which routes it receives without waiting for a provider change cycle each time the prefix set changes. Cisco BGP prefix-based ORF allows a receiving BGP speaker to send an inbound prefix-list filter to the remote peer, which then applies that list as an outbound filter. This reduces unwanted routing updates before they cross the session and lets the enterprise update the desired prefixes locally when business requirements change. Requesting only fixed prefixes from the ISP would work initially but fails the flexibility requirement because the provider has a two-week change process. Requesting a full table and filtering inbound would provide flexibility but wastes memory and CPU on the customer router because all routes are still received before filtering. A maximum-prefix limit does not select the correct routes. ORF is therefore the scalable operational design for receiving a default route and selected prefixes with minimal provider involvement. Reference topics: BGP ORF, prefix-based filtering, inbound route control, ISP peering design, routing table scale.

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.