ACE-L3-DCENG ACE - L3 - Specialist Data Center Engineering Practice Questions
Prepare for ACE-L3-DCENG with more than an answer.
- Exam fee
- $295 USD
- Level
- Specialist (Level 3)
- Valid for
- 2 years
Domains covered on the exam 4
- Layer 2 Leaf-Spine Design and Technologies25%
- Layer 3 Leaf-Spine Design and Underlay Routing25%
- VXLAN and EVPN Overlay30%
- CloudVision Platform20%
- 1
A Managed Service Provider (MSP) uses CloudVision Portal (CVP) configlets to manage their L2LS deployments. A junior engineer bypassed CVP and made manual CLI changes to a Leaf switch to add a new VLAN. When you view the device in CVP, it shows as out of compliance. What is the correct CVP workflow to integrate this manual change into the CVP configuration baseline?
Show answer details
Correct answer: B
When manual CLI changes cause a drift between the CVP Designed Configuration and the device's Running Configuration, CVP flags the device as non-compliant. The 'Reconcile' workflow allows administrators to view the diff and choose to either overwrite the CLI changes (pushing CVP config) or import the CLI changes into a new or existing configlet, bringing the device back into compliance.
- 2
At a university campus data center, an unauthorized user connects a small unmanaged switch to an access port on an Arista leaf switch and creates a loop. The port is configured with 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. The port immediately transitions to an errdisable state.
To ensure the port recovers automatically after 5 minutes once the rogue switch is removed, which global configuration command must be applied?
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Correct answer: B
When BPDU Guard triggers, it places the port into an errdisable state. To allow the switch to automatically recover from this state, two global commands are required: 'errdisable recovery cause bpduguard' (to enable automatic recovery specifically for BPDU violations) and 'errdisable recovery interval ' (to define the wait time, which is 300 seconds for 5 minutes).
- 3
A network architect is designing a new data center fabric that will eventually scale to over 200 leaf switches. They are deciding between OSPF and BGP for the underlay routing protocol. What is the primary technical justification for choosing BGP over OSPF in large-scale L3LS designs?
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Correct answer: B
In massive scale data centers (e.g., >100 leafs), OSPF's SPF calculations and link-state advertisement (LSA) flooding can become highly CPU-intensive, leading to convergence issues. BGP, specifically eBGP, scales much better because it relies on distance-vector mechanics (processing prefixes rather than a full topology map) and offers highly granular routing policies. EVPN-VXLAN can run over OSPF, but BGP is the industry standard for large underlays.
- 4
A global media broadcasting company is designing a new data center to support legacy uncompressed video rendering applications. These applications require strict Layer 2 adjacency across hundreds of server racks and cannot support routed gateways at the Top of Rack (ToR). Which design approach is the MOST optimal for this specific requirement?
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Correct answer: B
For environments that strictly require massive Layer 2 domains across all racks without overlay technologies, a Layer 2 Leaf-Spine (L2LS) architecture is required. In Arista L2LS designs, spines are typically configured as an MLAG pair to provide active-active redundant Layer 2 paths from the leafs, preventing STP blocking while extending the broadcast domain. Pure L3LS without an overlay cannot provide L2 adjacency. While EVPN-VXLAN could provide this, an L2LS fabric is the direct, traditional answer for native L2 scaling without overlay complexity.
- 5
During a greenfield deployment of an Arista Layer 2 Leaf-Spine (L2LS) fabric for a multi-tenant VMware environment, you need to configure inter-VLAN routing. The architect wants to ensure that the default gateway for each VLAN exists on the Spine switches to centralize routing policies. Which interface type MUST be configured on the Arista Spine switches to achieve this?
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Correct answer: B
In an L2LS architecture where routing is centralized at the spine layer, Switch Virtual Interfaces (SVIs) must be used. SVIs (configured as 'interface Vlan X') provide the Layer 3 gateway for hosts within a Layer 2 broadcast domain that spans multiple physical links and switches. Routed sub-interfaces are only applicable to point-to-point Layer 3 links and cannot act as a distributed gateway for a trunked VLAN spanning multiple leaf switches.
- 6
A large healthcare provider is experiencing periodic network outages in their legacy Arista L2LS data center. The architecture consists of 4 Spine switches and 20 Leaf switches. The network engineers notice that during link flaps on Leaf-15, a topology change occurs, and traffic across the entire fabric halts for several seconds. Upon investigation, you discover that Leaf-15 was inadvertently elected as the STP Root Bridge.
To permanently resolve this and align with Arista best practices for an L2LS design utilizing MLAG at the spine layer, how should the Spanning Tree Protocol (STP) root priorities be configured?
flowchart TD S1[Spine-1] --- L1[Leaf-1] S1 --- L2[Leaf-15] S2[Spine-2] --- L1 S2 --- L2 S1 -. MLAG Peer-Link .- S2Show answer details
Correct answer: B
In an Arista L2LS architecture using MLAG at the spine layer, the MLAG spine pair should act as a single logical unit and MUST be the STP root for all VLANs. Best practice dictates setting the STP priority of both MLAG spine switches to 0 (or the lowest possible value) to ensure they always win the root election. Leaf switches should be left at the default priority (32768) or higher to prevent them from ever becoming the root bridge, which would cause suboptimal traffic flow and potential outages during topology changes.
