Cisco Updated 400-007 Exam Questions and Answers by saul

C (Both modes use control packets):Regardless of whether echo packets are used, BFD asynchronous mode always relies on periodic transmission of control packets to verify session liveliness.

E (Echo mode uses separate packets):When echo is enabled, the echo packets are transmitted in addition to control packets, providing even faster failure detection by relying on data plane processing.

Other options explained:

A: Control and echo packets are never combined into a single packet.

B: Both modes always use control packets; echo packets are optional.

D: BFD echo packets are locally looped, not reflected back from the remote device.

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.

Reducing BGP keepalive and hold timers can help improve convergence but must be done carefully in provider-managed networks:

A: The service provider must agree to support modified timers on both PE and CE; otherwise, mismatched timer settings can break neighbor relationships.

C: The service provider may need to schedule configuration changes on PE routers to synchronize the timer adjustments and avoid service interruptions.

Why other options are incorrect:

B: Peer groups simplify policy application but do not impact BGP timers directly.

D: The number of routes affects convergence processing but not directly tied to timer adjustment.

E: The number of VRFs is a scalability consideration but unrelated to BGP timer negotiation.

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