Cisco Updated 400-007 Exam Questions and Answers by mikael

To conserve IPv4 addresses and achieve fast convergence:

B: Using /31 subnets for point-to-point (P2P) links enables each link to consume only two IP addresses. This is widely supported and conserves address space.

C: A hub-and-spoke design with P2P links minimizes the number of neighbor relationships and simplifies routing convergence.

Other options:

A: Multipoint Metro-E introduces neighbor adjacency complexity and DR/BDR elections, which delay convergence.

D: Aggregation is more applicable to prefix summarization, not address conservation per link.

E: DR/BDR roles apply only in broadcast/multicast environments, not P2P links.

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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.