Cisco 400-007 - Cisco Certified Design Expert (CCDE v3.1)

In this scenario, the application itself duplicates data transmission across two separate NICs on Host A, with the intention that at least one copy will reach Host B, regardless of any single path or link failure. While this increases redundancy at the application and host level, the underlying network must also support rapid failure recovery to avoid packet loss during convergence events.

Among the options provided:

A. EIGRP with feasible successors provides pre-computed backup routes but still requires routing protocol convergence upon failure, which could result in millisecond-scale interruption—enough to cause data loss if packets are in transit.

B. BFD (Bidirectional Forwarding Detection) offers rapid detection of link failures, but by itself does not provide traffic redirection or packet protection; it simply informs the routing protocol faster.

D. Static routes lack dynamic convergence capabilities and would not offer high availability across dynamic failure points unless manually configured with tracking—still less responsive and scalable.

C. IP Fast Reroute (IP FRR) is specifically designed to offer sub-50ms convergence time by pre-installing backup paths in the forwarding plane. Upon detecting a failure, traffic is immediately switched to the pre-computed alternate path without waiting for the routing protocol to reconverge. This ensures minimal disruption and best supports lossless delivery for high-availability applications.

IP FRR is consistent with CCDE v3.1 design principles where sub-second convergence and resiliency are critical in mission-critical enterprise and data center architectures.

B (OpenFlow):OpenFlow is a widely used SDN southbound protocol that enables controllers to directly manage forwarding tables of switches.

D (Open vSwitch Database - OVSDB):OVSDB is used by SDN controllers (especially in virtualized environments) to manage configuration state and flow entries on Open vSwitch instances.

Other options explained:

A/C: Non-existent protocols.

E: NetFlow is a traffic monitoring protocol, not a control interface for SDN controllers.

A (Working design over documentation):Agile prioritizes functional working solutions over exhaustive documentation, allowing continuous delivery and adaptability during the project lifecycle.

Other options explained:

B: Agile favors customer collaboration over contract negotiation.

C: Agile favors responding to change over rigid planning.

D: Agile favors individuals and interactions over processes and tools.

Route Distinguishers (RDs) are fundamental to MPLS Layer 3 VPN architecture (RFC 4364). They allow the service provider to distinguish identical IP prefixes from different VPN customers by adding a unique identifier to each VPN route, preventing conflicts from overlapping IP spaces.

Unique RDs ensure that the VPNv4 address family maintains separation of identical customer prefixes.

Why other options are incorrect:

B: Route Targets control route import/export policy but do not differentiate overlapping prefixes.

C: NAT is not required inside MPLS VPN for overlapping IPs.

D: VRF IDs are local identifiers on routers; not relevant for prefix uniqueness in control plane.

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Software-Defined Networking (SDN) architecture is based on the logical decoupling of the control and data planes. According to the SDN reference model, the architecture typically includes the following planes:

Control Plane: This resides in the SDN controller and is responsible for decision-making, including route and policy calculations.

Application Plane: This layer contains business and network applications (e.g., firewalls, QoS policies) that communicate with the controller to request services and enforce policy.

These planes are essential in SDN architecture:

The control plane programs the forwarding behavior of network elements.

The application plane interacts via northbound APIs to define intent and service logic.

Options such as “Software plane” and “Network plane” are vague or not used in the SDN context. The “Management plane” is a separate functional layer and is not part of the architectural definition core to SDN as per CCDE v3.1.

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B (Separate priority queues): Both VoIP and the custom stock-trading application require low latency and jitter guarantees but serve different business functions. Best practice is to place them in separate priority queues to prevent one application's bursts from affecting the other, ensuring deterministic service levels for both mission-critical services.

Other options explained:

A: Sharing queues may lead to competition between traffic types, risking SLA violations.

C/D: CBWFQ is not sufficient for true low-latency guarantees; priority queuing is required.

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The IS-IS Overload Bit allows a router to signal to its peers that it should be temporarily excluded from SPF calculations for transit traffic:

A: The Overload Bit can be automatically set at startup (known as "startup overload") to allow the router sufficient time to converge IGP, BGP, and stabilize protocols before accepting transit traffic.

D: The bit can remain set until all dependent protocols have converged and the router is fully operational.

Why other options are incorrect:

B: The router’s directly connected prefixes remain reachable; only transit path calculations exclude the overloaded node.

C: MPLS-TE does not automatically reoptimize tunnels based on the Overload Bit.

E: There is no specific restriction preventing Overload Bit usage on Route Reflectors.

C: GLOP addressing is defined in RFC 2770, assigning a portion of the 233.0.0.0/8 range for each AS based on their 16-bit ASN. This allows each AS to use a /24 of globally unique multicast addresses without coordination from IANA.

Other options:

A: 239.0.0.0/8 is the administratively scoped multicast address space.

B: 224.0.0.0/24 is reserved for local link-scoped protocols (e.g., OSPF, RIP).

D: 232.0.0.0/8 is the Source-Specific Multicast (SSM) range.

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