300-420 Exam Dumps : Designing Cisco Enterprise Networks (ENSLD) v1.1

In Cisco SD-Access, an intermediate node is an underlay transit device. Its responsibility is to provide IP reachability between fabric edge nodes, border nodes, and other fabric infrastructure roles. Intermediate nodes forward routed underlay traffic and do not perform endpoint registration, endpoint lookup, or VXLAN encapsulation for user traffic. Endpoint-to-location mapping is handled through the fabric control plane, which is based on LISP map-server and map-resolver functions. Fabric edge nodes identify connected endpoints, apply policy, act as anycast gateways, and encapsulate user traffic into VXLAN. Border nodes connect the fabric to external networks and handle traffic entering or leaving the fabric. The intermediate node is therefore comparable to a routed distribution or core transport device in a traditional hierarchical campus, except it is participating in the SD-Access underlay. It must provide stable Layer 3 reachability and appropriate MTU for encapsulated traffic but does not maintain the host tracking database or add security group information to VXLAN headers. The correct function is transporting IP packets between edge and border nodes.

Advertising more-specific prefixes toward the preferred service provider is the correct way to influence inbound traffic to enter through a chosen CE interface. BGP inbound path control is indirect: the enterprise cannot set local preference inside remote autonomous systems, and MED is honored only under specific provider policies. The most deterministic option available to the customer is to advertise a longer-prefix route to the preferred provider because Internet and BGP route selection generally prefer the longest matching prefix before BGP path attributes are considered. If the aggregate is advertised to both providers but a more-specific route is advertised to the provider connected to gig0/0, return traffic for that more- specific destination is attracted through that interface. Lowering MED toward the less preferred provider is the opposite of the desired effect. AS-path prepending toward the preferred provider would make that path less attractive. Local preference affects outbound path selection inside the local AS, not inbound traffic from external networks. Reference topics: BGP inbound traffic engineering, longest-prefix match, route aggregation, AS-path prepending, MED, local preference.

The requirement for end-to-end path verification identifies the Integrated Services model with RSVP. IntServ uses per-flow resource reservation, and RSVP signals the path between sender and receiver so devices along that path can admit or reject the requested service based on available resources. This makes IntServ appropriate when the design requires explicit end-to-end path validation and reservation for application flows. DiffServ works differently. In a DiffServ design, traffic is marked, normally with DSCP or CoS at the edge, and each hop applies a configured per-hop behavior. DiffServ is scalable and common in enterprise WAN and campus QoS designs, but it does not perform per-flow signaling or verify that every device in the path can reserve the requested resources. Marking traffic at the access layer is an important QoS design practice, but marking alone is not path verification. Therefore, when the customer explicitly requires end-to-end path verification for business-critical traffic, Cisco QoS architecture points to IntServ with RSVP rather than a pure DiffServ marking model.