* C (Layer 2 switches unaffected):IPv6 operates at Layer 3, so pure Layer 2 switches forward frames without needing IPv6 awareness. As long as switches can transparently forward Ethernet frames, IPv6 functionality will be preserved, minimizing unnecessary hardware upgrades.
Other options explained:
* A/B/D: These unnecessarily increase cost and complexity for basic Layer 2 functionality where IPv6 awareness is not mandatory.

* D: CWDM (Coarse Wavelength Division Multiplexing) shares parts of the same optical transmission window (1260-1625 nm) as DWDM but uses wider spacing between channels (typically 20 nm apart).
* E: CWDM typically uses passive devices (multiplexers and demultiplexers) that require no electrical power, making deployment cost-effective.
Incorrect Options:
* A: CWDM is better suited for shorter distances (up to ~80 km) and doesn't typically use optical amplifiers (EDFA). DWDM is better for long-haul with amplification.
* B: 850 nm is used in multimode fiber systems (not CWDM).
* C: CWDM supports up to 18 channels; DWDM supports up to 32 or more.

* C (Push-based):Push notifications to a registered device (typically a phone) are used as a second authentication factor.
* D (Possession-based):Possession factor includes physical tokens, smart cards, or registered devices - verifying that the user possesses something unique.
Other options explained:
* A/B/E: Not valid MFA factors under standard authentication frameworks.

BFD (Bidirectional Forwarding Detection) operates by exchanging control packets between peers, typically using UDP encapsulation. In single-hop deployments, BFD sessions are often established using:
* Source IP = destination IP = local interface IP (identical source and destination addresses), especially in certain implementations like Cisco single-hop BFD.
* This allows rapid fault detection without routing dependency.
The IPS must permit these packets to avoid disrupting BFD functionality.
Why other options are incorrect:
* A: Fragmentation is irrelevant to BFD.
* B, C, D, F: BFD does not use broadcast, multicast, or 0.0.0.0 addresses.
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During massive BGP update events (such as after a topology change), a route reflector may struggle processing both BGP updates and the resulting TCP acknowledgments required for reliable BGP session communication.
Increasing the hold queue size allows the router to buffer more packets waiting for processing (including TCP acknowledgments), helping the router handle bursts of BGP updates without dropping TCP segments or tearing down sessions.
This queue tuning is a well-known scalability optimization in CCDE v3.1 when designing route reflector clusters handling large-scale control plane updates.
Why other options are incorrect:
* B & C: Adjusting buffer sizes does not directly address TCP acknowledgment backlog.
* D: Keepalive timers control session liveliness, not update processing.
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