An engineer configured Layer 2 extension from the ACI fabric and changed the Layer 2 unknown unicast policy from Flood to Hardware Proxy. How does this change affect the flooding of the L2 unknown unicast traffic?
Answer(s): A
Option A is correct because enabling Hardware Proxy for L2 unknown unicast in a Layer 2 extension from the ACI fabric directs unknown unicast traffic to a spine proxy, reducing flooding and offloading to the spine. Incorrect — B: Flooding within the whole fabric is not used when hardware proxy is active. C: Dropping by the leaf when destination is absent describes unknown unicast behavior without proxy, which is not the configured behavior. D: Forwarding to APICs for proxy is not applicable; APICs do not perform L2 unknown unicast proxy for this scenario.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/2-x/L2_config/ b_Cisco_APIC_Layer_2_Configuration_Guide/b_Cisco_APIC_Layer_2_Configuration_Guide_chapter_010.html
When the subnet is configured on a bridge domain, on which physical devices is the gateway IP address configured?
Answer(s): C
Option C is correct because in ACI when a subnet is configured on a bridge domain, the gateway IP is configured on the leaf switches (where the bridge domain is present) that serve as endpoints for external connectivity. ACI uses leaf-based gateway routing for tenant VRFs in this scenario.A) Incorrect — spine nodes do not host bridge-domain subnet gateways; gateways are not provisioned on spine-only devices.B) Incorrect — gateway IPs are not configured on spine switches; only leaves hosting the BD participate.D) Incorrect — border leaf nodes are not a separate category; the gateway is placed on the leafs for the BD, not a subset termed “border leaves.”
http://www.netdesignarena.com/index.php/2016/06/16/aci-tenant-building-blocks-forwarding-logic/
Which method does the Cisco ACI fabric use to load-balance multidestination traffic?
Option A is correct because the Cisco ACI fabric uses forwarding tag trees to load-balance multidestination traffic by distributing flows across multiple paths based on traffic engineering and endpoint information, enabling efficient ECMP-like behavior within the fabric. B) Incorrect — PIM routing is a multicast protocol not used for multidestination load balancing within the ACI fabric; ACI relies on its own forwarding constructs rather than PIM for fabric-wide balance.C) Incorrect — Spanning trees are avoided in ACI fabric to enable multipath and loop-free topology without relying on STP for load balancing.D) Incorrect — Shortest-path trees are a general concept in routing but not the mechanism ACI uses to load-balance multidestination traffic across the fabric.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-x/aci-fundamentals/b_ACI- Fundamentals/b_ACI-Fundamentals_chapter_010010.html
What happens to the traffic flow when the Cisco ACI fabric has a stale endpoint entry for the destination endpoint?
Answer(s): D
Option D is correct because a stale endpoint entry causes the fabric to misroute traffic to the incorrect destination leaf, given the endpoint’s location is not accurately tracked, leading to traffic being steered based on outdated topology data. A) Incorrect — data plane learning learns source endpoints; stale entries do not prevent learning of the source. B) Incorrect — the fabric does not simply drop traffic due to a stale entry; traffic is redirected to a wrong leaf. C) Incorrect — flooding would occur if there were no known destination or in certain failure states, not specifically due to a stale endpoint entry.
https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/ white-paper-c11-739989.html
Refer to the exhibit. A systems engineer is implementing the Cisco ACI fabric. However, the Server2 information is missing from the Leaf 101 endpoint table and the COOP database of the spine. The requirement is for the bridge domain configuration to enforce the ACI fabric to forward the unicast packets generated by Server1 destined to Server2. Which action must be taken to meet these requirements?
Answer(s): B
Option B is correct because: Setting L2 Unknown Unicast to Flood ensures unicast traffic to destinations without a known MAC address (Server2 missing from endpoint tables) is broadcast/flooded at the L2 data plane, enabling forwarding of Server1→Server2 traffic within the bridge domain regardless of COOP database gaps.A) Incorrect — ARP Flooding would affect ARP requests, not general L2 unknown unicast forwarding for data-plane traffic between endpoints missing in endpoint tables.C) Incorrect — IP Data-Plane Learning to No prevents learning of IP-to-MAC mappings, breaking forwardability rather than enabling it.D) Incorrect — Enabling Unicast Routing activates inter-VRF/unicast routing, not needed for bridging-domain unicast flood behavior.
An engineer must allow multiple external networks to communicate with internal ACI subnets. Which action should the engineer take to assign the prefix to the class ID of the external Endpoint Group?
Option C is correct because enabling External Subnets for External EPG allows the external network prefixes to be associated with the class ID of the external Endpoint Group, enabling proper routing and policy application between external networks and internal ACI subnets.A) Incorrect — Export Route Control Subnet for the External EPG flag is not the mechanism to assign external prefix to the EPG class ID; it pertains to exporting routes rather than internal/external prefix association.B) Incorrect — Enabling an L3Out with Shared Route Control Subnet is not the direct method to map external prefixes to the External EPG class ID; it concerns route control sharing rather than per-subnet assignment.D) Incorrect — Import Route Control Subnet flag is related to importing routes, not specifically to assigning the prefix to the External EPG class ID.
An engineer must ensure that Cisco ACI flushes the appropriate endpoints when a topology change notification message is received in an MST domain. Which three steps are required to accomplish this goal? (Choose three.)
Answer(s): C,E,F
Option C is correct because binding the spanning tree policy to the switch policy group ensures the MST domain’s STP behavior is applied to the relevant switches, enabling proper endpoint flush on topology changes. Option E is correct because creating a new region policy under the spanning tree policy defines the MST region mapping and region-specific behavior required for correct topology change handling. Option F is correct because mapping VLAN ranges to MST instance numbers ensures the correct MSTI associations are used during topology changes. A, B, D are incorrect: A and B pertain to interface-level STP controls not region-level MST handling; D is redundant once the policy group is bound; F/Specifics of A and B do not align with MST region changes. INSUFFICIENT_KNOWLEDGE
A Cisco ACI bridge domain and VRF are configured with a default data-plane learning configuration. Which two endpoint attributes are programmed in the leaf switch when receiving traffic? (Choose two.)
Answer(s): D,F
Option D is correct because, with default data-plane learning in a bridge domain/VRF, the leaf programs Local MAC and IP for locally originated traffic to enable proper ARP/MAC learning and forwarding. Option F is correct because Remote IP is also learned from the remote endpoint to support flow-based forwarding and policy application. Incorrect — A: Remote MAC and IP are not both learned as a pair in this scenario; the local MAC is what is programmed for local endpoints. Incorrect — B: Remote Subnet is not a programmed data-plane attribute. Incorrect — C: Local IP with not MAC is not how the data plane learns endpoints. Incorrect — E: Local Subnet is not the programmed data-plane attribute.
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