300-420 Exam Dumps : Designing Cisco Enterprise Networks

Integrated Services is the QoS model that allows an application to signal its traffic requirements to the network and request specific service treatment. Cisco QoS guidance distinguishes IntServ from DiffServ by explaining that IntServ follows a signaled-QoS model, while DiffServ uses provisioned per-hop behavior based on markings. IntServ uses RSVP to reserve resources along the end-to-end path. That reservation process allows the network to admit or deny the flow based on available bandwidth and policy, which is why IntServ aligns with applications that require consistent and dedicated bandwidth. DiffServ is much more scalable and widely deployed in enterprise networks, but it does not provide per-flow resource reservation by itself. LLQ is a queuing mechanism commonly used inside a DiffServ design for delay-sensitive traffic such as voice. WRED is a congestion-avoidance technique, not an end-to-end reservation architecture. Because the question explicitly says that the application informs the network of its traffic profile and requests a service level, the correct QoS architecture is IntServ.

Bandwidth percentage with policing is the correct QoS approach. The requirement has two separate parts: each subnet must receive a minimum share during congestion, and no subnet should introduce delay into download traffic. Bandwidth percentage is used to allocate a minimum bandwidth guarantee among classes during congestion while still allowing a class to use unused bandwidth when other classes are idle. Policing enforces a rate by dropping or remarking excess traffic rather than buffering it. That behavior is important because the question explicitly says download traffic must never experience delay. Shaping would be wrong because shaping buffers excess packets and transmits them later, which intentionally adds delay. Rate- limiting is a broad term, but when the design choice offers policing explicitly, policing is the precise mechanism that matches the no-delay requirement. A parent or class policy can reserve 25 percent per subnet on a 40 Mbps service, giving each subnet 10 Mbps during congestion while unused bandwidth remains available. Reference topics: CBWFQ bandwidth percent, traffic policing, shaping versus policing, Internet edge QoS, congestion management.

Bidirectional PIM is the correct multicast protocol for this many-to-many financial application. The question states that most multicast sources also receive multicast traffic and that the design must not use source trees. Cisco describes BIDIR-PIM as a multicast mode built for many-to-many applications that use a shared tree rooted at the rendezvous point and avoid per-source shortest-path trees. This reduces multicast state because routers do not maintain separate source/group state for every active sender. PIM Sparse Mode can start with a shared tree, but it can switch to source trees, which violates the stated requirement. PIM-SSM is explicitly source-specific and requires receiver knowledge of the source, so it is not appropriate for a many-to-many model where source trees are disallowed. MSDP is not a multicast forwarding mode; it is used for source discovery between PIM-SM domains. The option text contains a spelling error, but the intended answer is BIDIR-PIM. The architect should verify RP placement, Designated Forwarder behavior, group ranges, and whether the application can tolerate shared-tree forwarding rather than shortest-path source trees. Reference topics: BIDIR-PIM, many-to-many multicast, shared tree, source-tree avoidance, multicast scaling.