300-420 Exam Dumps : Designing Cisco Enterprise Networks

IntServ with RSVP is the correct model when an application must request a specific service level and receive guaranteed bandwidth or delay treatment. Cisco describes the Integrated Services model as a flow-based QoS architecture in which applications signal their resource requirements to the network. RSVP is the signaling protocol used to reserve resources along the path. This differs from DiffServ, which marks packets and applies per-hop behavior without creating per-flow reservations. The question states that the application can request a particular type of service to support its delay requirements and that bandwidth must be guaranteed. Those are classic IntServ and RSVP characteristics. DiffServ with DSCP is scalable and widely used in enterprise networks, but it cannot guarantee resources end to end unless every hop is engineered and provisioned accordingly. IntServ with DSCP is not the standard model because RSVP is the reservation mechanism. Reference topics: Integrated Services, RSVP, resource reservation, guaranteed service, QoS architecture, delay-sensitive applications.

Running BFD between EIGRP neighbors is the appropriate design when the problem is traffic loss during link failure and the requirement is to reduce the impact of the failure. EIGRP can detect neighbor loss through its hello and hold timers, but those timers may not be fast enough for applications sensitive to packet loss. Bidirectional Forwarding Detection provides rapid failure detection independent of the routing protocol’s normal timer expiration. When BFD detects a failed forwarding path, it notifies EIGRP so the routing process can converge without waiting for the EIGRP hold timer. Summarization is still a valuable scaling technique, but it primarily reduces route table size and query scope; it does not directly accelerate failure detection on an individual inter-router link. Reducing EIGRP hello and hold timers can improve detection, but it increases control-plane load and is less efficient than BFD. The question emphasizes data loss when any one link fails, so fast failure detection is the best corrective design. Reference topics: EIGRP convergence, BFD, failure detection, hello and hold timers, routed-link resiliency.

Root guard is the correct feature when the design must allow switches to be attached for testing but prevent those switches from influencing the spanning-tree root placement. Cisco root guard protects the intended STP root by placing a port into a root-inconsistent state if superior BPDUs are received on a port where the root should never appear. This directly addresses the risk created by rogue or lab switches connected by end users: if a user switch advertises a better bridge priority, the production access topology is not allowed to reconverge around that unauthorized device. BPDU guard is usually used on PortFast edge ports to err-disable a port that receives any BPDU, which is excellent for strict host-only ports but less aligned with the wording that users may connect their own switches for testing. Loop guard protects root or alternate ports from losing BPDUs and accidentally forwarding. BPDU skew detection is a diagnostic feature, not the correct design control. Therefore, root guard is the appropriate protection against rogue switches affecting STP topology. Reference topics: STP root placement, root guard, superior BPDUs, campus Layer 2 protection.