ACE-L3-DCENG Sample Questions & Answers
VXLAN design and EVPN fundamentals carry the biggest share, ahead of building the leaf-spine fabric at both Layer 2 (VLANs and spanning tree) and Layer 3 (underlay routing), and CloudVision provisioning with studios.
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Real questions from the ACE - L3 - Specialist Data Center Engineering practice test — answers and explanations included. Showing 6 of 12 free samples.
- Question 1IntermediateSelect 2
Layer 2 Leaf-Spine Design and Technologies · LACP
A storage administrator reports that a new high-performance NVMe-over-Fabrics storage array connected via an 8-port LACP port-channel is only utilizing a single 100G link, despite generating massive 'elephant flows'. You verify that LACP is formed correctly in active mode. Which TWO configurations or actions will help optimize the traffic distribution across the port-channel members? (Select TWO)
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Correct answers: B, D
LACP load balancing relies on a hashing algorithm to pin flows to specific physical links. If traffic consists of 'elephant flows' (large, long-lived streams), a simple MAC or IP hash might map all traffic to one link. Including Layer 4 port information increases the entropy of the hash, allowing different sessions between the same IPs to be distributed across multiple links. Additionally, enabling dynamic load balancing (if supported by the platform/profile) can rebalance flowlets.
LACP load balancing relies on a hashing algorithm to pin flows to specific physical links. If traffic consists of 'elephant flows' (large, long-lived streams), a simple MAC or IP hash might map all traffic to one link. Including Layer 4 port information increases the entropy of the hash, allowing different sessions between the same IPs to be distributed across multiple links. Additionally, enabling dynamic load balancing (if supported by the platform/profile) can rebalance flowlets.
- Question 2Intermediate
Layer 2 Leaf-Spine Design and Technologies · MLAG
A financial institution's network operator receives an alert that the MLAG peer-link between two Arista ToR switches has gone down. However, the out-of-band management network is fully operational, meaning the MLAG heartbeat is still up. What is the expected behavior of the MLAG secondary peer in this specific split-brain scenario?
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Correct answer: C
In an Arista MLAG environment, if the peer-link goes down but the heartbeat remains up, the system recognizes a split-brain scenario. To prevent loops and MAC flapping, the MLAG secondary switch will automatically place all of its MLAG member ports into an errdisable (down) state. Orphan ports (ports not part of an MLAG) will remain up and active. If the heartbeat also fails, both switches would assume the primary role, which is why the heartbeat is critical.
- Question 3Beginner
Layer 2 Leaf-Spine Design and Technologies · Default Gateway Redundancy (FHRP)
True or False: Unlike VRRP, Arista's Virtual ARP (VARP) requires a dedicated control plane election process to determine which switch actively forwards traffic for the virtual gateway MAC address.
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Correct answer: B
False. Unlike VRRP, which relies on hello packets and an election process to determine an active Master router, VARP (Virtual ARP) is completely stateless. There is no control plane protocol or election process. All switches configured with the same VARP virtual MAC and virtual IP address will actively route traffic destined to that MAC address, providing an inherent active-active gateway without protocol overhead.
- Question 4Intermediate
Layer 2 Leaf-Spine Design and Technologies · Default Gateway Redundancy (FHRP)
A cloud service provider is migrating their default gateways from a legacy VRRP setup to Arista VARP to achieve true active-active forwarding across their MLAG leaf pairs. When configuring VARP on the Arista switches, which command is required globally to define the MAC address that all hosts will resolve for the gateway?
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Correct answer: B
To configure VARP on Arista EOS, you must define a global virtual MAC address using the 'ip virtual-router mac-address ' command. This MAC address is shared across all switches acting as the VARP gateway. Subsequently, the 'ip virtual-router address ' command is applied at the SVI interface level. Unlike VRRP, VARP does not use a protocol-derived MAC address automatically.
- Question 5Advanced
Layer 2 Leaf-Spine Design and Technologies · MLAG
An e-commerce company uses an Arista MLAG pair at the Top of Rack. Due to a hardware issue, Leaf-A reloads. When Leaf-A finishes booting, the MLAG peer-link establishes, but Leaf-A immediately suspends its orphan ports (single-attached servers) for a configured duration before bringing them online. What is the primary technical reason for this behavior?
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Correct answer: B
This behavior is controlled by the 'reload-delay' feature in MLAG. When an MLAG peer reboots, its L2/L3 tables are empty. If it brings up its access ports (including orphan ports) immediately, it will blackhole traffic because it hasn't learned the MAC addresses or routing table entries from its peer. The reload-delay timer suspends these ports until the control plane has fully synchronized across the peer-link.
- Question 6Beginner
Layer 2 Leaf-Spine Design and Technologies · Building L2LS Fabric
You are building a new L2LS fabric using the Arista EOS CLI. When configuring MLAG on the two spine switches, you must assign a specific identifier that allows the two switches to present themselves as a single logical switch to downstream devices. Which configuration parameter handles this requirement?
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Correct answer: B
Under the MLAG configuration mode, the 'domain-id' is mandatory and must match on both MLAG peers. The domain ID is used to derive the MLAG system MAC address (unless manually configured), which is the LACP system ID presented to downstream devices. This makes the two physical switches appear as a single LACP partner.
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