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.

R3 must be made an L1/L2 router so that it can connect the Level 1 area to the Level 2 backbone. IS-IS uses a two-level hierarchy. Level 1 routers know the topology inside their local area, Level 2 routers form the backbone between areas, and Level 1/Level 2 routers provide the boundary between the two. A proper IS-IS backbone cannot have isolated Level 1-only routers positioned between L1/L2 routers that need to exchange interarea reachability. If the link failure exposed an area-continuity problem, converting R3 to L1/L2 gives the area an appropriate attachment point to the backbone and restores interarea forwarding behavior. Making an unrelated router Level 1 or Level 2 only would not necessarily create the required boundary function. Simply making Area 0 L2-only is also not the focused fix if the topology still lacks a correct L1/L2 transition point. The design principle is straightforward: every Level 1 area must have a dependable L1/L2 router through which traffic can reach destinations outside the area. Reference topics: IS-IS Level 1, Level 2 backbone, L1/L2 routers, interarea reachability, hierarchical IGP design.

Dual multihomed is the only listed WAN design that satisfies all failure conditions: CE, PE, ISP, and link failure. A single-homed design has one provider attachment and cannot survive most of those events. A single multihomed design uses more than one provider or provider connection, but if it still has only one customer edge device, a CE failure remains a single point of failure. A dual-homed design can provide multiple links to one provider, but it may not protect against a complete ISP failure. Dual multihoming combines redundant customer edge devices with connections to multiple provider edge devices and, typically, multiple providers. Cisco WAN and BGP design guidance uses multihoming to increase availability, control inbound and outbound path selection, and avoid dependence on a single provider path. This design gives the architect the necessary device, link, and provider diversity. Reference topics: WAN edge redundancy, BGP multihoming, dual-provider design, CE and PE resiliency, internet edge high availability.