Pass the Cisco CCDE v3.0 400-007 Questions and answers with CertsForce

OSPF throttling timers control the pacing and frequency of SPF calculations and LSA generation. They help strike a balance between fast convergence and control-plane stability. The key timers include:

LSA generation throttling (min/max interval between LSA originations)

SPF calculation throttling (delays between consecutive SPF runs)

By tuning these timers, network designers can:

Prevent CPU overload caused by rapid or repeated LSA updates due to flapping links

Smooth out instability while still enabling responsive convergence

This approach aligns with CCDE v3.1 under “Protocol Design Implications” for optimizing IGP behavior in large, dynamic topologies.

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In the topology shown, the 10.10.0.0/16 network is redistributed into two different OSPF processes—OSPF 1 and OSPF 2—from router R3. The redistribution uses the external route types:

Into OSPF 1 as an E1 route with a metric of 100

Into OSPF 2 as an E2 route with a metric of 100

When redistribution occurs in OSPF, two types of external routes can be injected:

Type E1: Adds the internal OSPF cost to the external cost (total path cost = external metric + internal OSPF path)

Type E2: Considers only the external cost and ignores internal path cost (default behavior)

In this case:

The path via R2–R3 (E1) includes both the external cost and the internal cost from R1 to R2 to R3. That is: 10 (R1–R2) + 10 (R2–R3) + 100 (external) = 120.

The path via R4–R5–R3 (E2) will show a constant metric of 100 regardless of the internal OSPF path (10 + 10 = ignored).

So when the link between R2 and R3 fails, the path R1–R4–R5–R3 (E2 route with constant metric 100) becomes the preferred route.

However, when the link between R2 and R3 is restored, the E1 route will be recalculated as:

Internal cost (R1–R2–R3) = 10 + 10 = 20

External metric = 100

Total = 120

OSPF always prefers E1 routes over E2 routes when both are available, even if the E2 route appears to have a better metric. This is because E1 routes provide more accurate end-to-end cost calculation.

Therefore, upon restoration, the routing table reverts to the E1 route via R1–R2–R3.

This behavior is aligned with OSPF protocol standards and is emphasized in CCDE v3.1 under the “Protocol Design Implications” domain, which focuses on redistribution behaviors, route-type preferences, and convergence consistency in multi-domain IGP designs.

B: In transparent mode, the firewall operates at Layer 2 and can participate in STP to avoid loops.

C: Multicast traffic can traverse the firewall if allowed through transparent bridging rules.

Why other options are incorrect:

A: Transparent mode requires no change to IP addressing.

D: Transparent firewalls do not form routing adjacencies.

E: Routed mode firewalls operate at Layer 3; transparent mode does not insert router hops.

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In service provider Ethernet transport environments such as VPLS, Ethernet OAM (Operations, Administration, and Maintenance) is used to provide fault detection, monitoring, and troubleshooting capabilities. The two relevant components here are:

A (Unicast heartbeat messages between MEPs): Maintenance End Points (MEPs) are configured at the edges of the OAM domain (SP-SW1 and SP-SW2). Heartbeat messages can be used to proactively monitor and detect loss of continuity between the endpoints.

B (Enable Connectivity Fault Management): CFM (IEEE 802.1ag) provides end-to-end fault detection, continuity check messages (CCMs), loopback, and link trace mechanisms that operate between MEPs at Layer 2. CFM enables proactive detection of failures and service-level assurance across the provider’s Ethernet segment.

Other options explained:

C: Upward MEPs are not applicable here since these are typically used for customer-facing or hierarchical maintenance domains.

D: E-LMI (Ethernet Local Management Interface) operates between CE and PE for service activation—not applicable for SP-SW to SP-SW fault detection across VPLS.

E: LLDP (Link Layer Discovery Protocol) is for neighbor discovery on directly connected interfaces—not suitable for end-to-end fault detection across a VPLS domain.

This design solution aligns fully with CCDE v3.1 principles for service provider Layer 2 VPN design and Ethernet OAM integration.

B (Weighted Random Early Detection - WRED):WRED proactively drops packets before buffers are full to avoid global synchronization in TCP traffic and prevent tail drops, thus improving overall TCP performance under congestion.

Other options explained:

A: WFQ provides fairness but does not proactively avoid congestion.

C: LLQ is for delay-sensitive traffic, not congestion avoidance for TCP.

D: FIFO offers no QoS or congestion control.

The two most common challenges for organizations adopting container technologies are:

B (Security): Containers introduce unique security challenges, such as shared kernels, namespace isolation, image vulnerabilities, and orchestration exposure.

E (Skilled staff): Containerization requires specialized skills in orchestration (e.g., Kubernetes), CI/CD, and microservices design, which may not be readily available in many IT teams.

Other options explained:

A: Performance is generally good for containers; overhead is minimal.

C: Cost savings are often a driver for containerization.

D: Deployment is streamlined via orchestration platforms.

F: Compliance is important but less frequently cited as the initial adoption barrier.

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In the Cisco three-layer hierarchical design model (Access, Distribution, Core), the access layer is primarily responsible for:

Providing user/device connectivity.

Enforcing policy boundaries.

Performing QoS classification and marking at ingress.

The access layer is the optimal point to classify and mark traffic for QoS because:

It is the first point of entry into the network for end-user devices.

Markings can then be trusted by upstream devices (distribution and core).

This minimizes trust boundaries throughout the network and ensures consistent policy enforcement.

This design principle ensures end-to-end QoS consistency, a key objective emphasized in CCDE v3.1 for scalable and maintainable enterprise designs.

Why other options are incorrect:

A (Fault isolation): Typically handled at distribution/core layers.

C (Reliability): A general network-wide requirement, not specific to access.

D (Fast transport): Primarily a core layer function.

E (Redundancy and load balancing): Managed primarily at distribution and core layers.

GLOP addressing is defined in RFC 2770. It assigns globally unique multicast addresses based on an organization's ASN by mapping the 16-bit ASN into the middle two octets of the 233.0.0.0/8 address space.

233.0.0.0/8 is specifically reserved for GLOP addressing.

The uniqueness of the address is derived from the assigned ASN.

Why other options are incorrect:

A: 232.0.0.0/8 is SSM address space.

C: 239.0.0.0/8 is for administratively scoped multicast.

D: 224.0.0.0/24 is reserved for local multicast (link-local scope).

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A (DAI - Dynamic ARP Inspection): Prevents ARP spoofing attacks on the data plane.

B (IP Source Guard): Prevents IP address spoofing by verifying IP/MAC bindings against DHCP snooping tables.

Both are directly applied to securing the data plane (traffic forwarding layer).

Why other options are incorrect:

C (BEEP): A transport protocol, not a data plane security feature.

D (CPPr): Protects the control plane, not data plane.

E (MPP): Protects management plane, not data plane.

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B (Layer 3 MPLS VPN hub and spoke):A hub-and-spoke MPLS VPN allows scalable branch-to-data-center communication with efficient routing, simplified management, and adequate support for real-time video across 200 branches.

Other options explained:

A: DMVPN is flexible but not as scalable or deterministic for 200-site enterprise video conferencing.

C: VPLS operates at Layer 2 and may introduce unnecessary broadcast domain scaling challenges.

D: Full mesh MPLS is difficult to manage for such a large number of sites.