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

A (QoE estimation): In SDN-based designs, particularly for multimedia traffic (voice, video, streaming), Quality of Experience (QoE) estimation is crucial to ensure end-user satisfaction. SDN can dynamically allocate resources based on real-time measurements of packet loss, jitter, delay, and other QoE indicators to maintain service quality.

Other options explained:

B: Security is always important but not unique to multimedia design.

C: Traffic patterns are part of capacity planning but secondary to QoE for multimedia.

D: Flow forwarding is handled by the SDN controller but does not directly address multimedia quality.

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B (Micro loops):OSPF Loop-Free Alternates (LFA) pre-calculate backup next-hops to reduce transient micro loops during the convergence process when primary routes fail.

Other options explained:

A: DTP relates to trunk negotiation, not loop prevention.

C: STP handles Layer 2 loops.

D: REP is a Cisco Layer 2 redundancy protocol, unrelated to OSPF loop prevention.

C (Transparent firewall): Operates at Layer 2, allowing filtering and inspection of traffic within the same subnet without requiring IP routing changes. It performs deep packet inspection while maintaining Layer 2 adjacency, making it ideal for intra-subnet traffic control in data centers.

This allows security segmentation inside broadcast domains, enforcing security policies even for east-west traffic.

Other options explained:

A: Routed firewalls require subnet boundaries and are not ideal for intra-subnet control.

B: VLAN ACLs provide basic filtering but lack deep packet inspection capabilities.

D: Zone-based firewalls are primarily designed for inter-subnet (Layer 3) traffic segmentation.

When an ACL is applied inbound on the Internet gateway interface facing the internal (trusted) network, the source IP address seen in the ACL will be the address after NAT translation has been applied to outbound traffic. This is called the inside global address:

Inside global = Public IP assigned by NAT to inside traffic for external use.

Inside local = Internal IP address prior to NAT.

Why other options are incorrect:

B, D: Outside addresses refer to external devices, not internal traffic.

C: Inside local is seen before NAT, not after.

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EIGRP may be valid for initial deployment, but its scalability limitations — including proprietary nature, limited support over non-broadcast multipoint VPNs, and suboptimal convergence for large WAN overlays — make it most restrictive for future expansion.

BGP is typically the most scalable choice for large-scale VPN WAN deployments.

Why other options are incorrect:

B: IS-IS is not commonly deployed over Internet VPNs.

C: OSPF has better scalability than EIGRP for multi-area design but still limited over VPN overlays.

D: BGP is the preferred protocol for large-scale IPsec VPN WANs.

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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 and C: Adjusting buffer sizes does not directly address TCP acknowledgment backlog.

D: Keepalive timers control session liveliness, not update processing.

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EIGRP’s convergence time is heavily impacted by the size of the query domain — the group of routers involved when a route goes into active state. The larger the query domain, the longer the convergence. Summarization naturally bounds query propagation because routers receiving a summary have no knowledge of individual prefixes beyond that summary, preventing them from being queried about specifics they don’t track.

This design technique is emphasized in CCDE v3.1 because:

Summarization reduces the query scope.

Faster convergence happens as fewer routers process queries.

Hierarchical design is enabled for stability and scalability.

Why other options are incorrect:

A: Distribute lists filter prefixes but don ' t reduce query propagation.

B and C: Triangulated or squared physical topology doesn’t control protocol-level query scope.

E: Default routes may help limited routing domains but don’t optimize EIGRP convergence specifically.

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