ACI Endpoint Communication within Same EPG
A network engineer configures a Cisco ACI fabric with this configuration: • Endpoint-1 with an IP address 10.1.0.1/24 is attached to Leaf-101. • Endpoint-2 with an IP address 10.1.0.2/24 is attached to Leaf-102. • Both endpoints are in EPG-A. • The bridge domain for EPG-A is called BD-A and contains a single subnet 10.1.0.254/24. • Endpoint-1 cannot reach Endpoint-2. Which action allows Endpoint-1 to communicate with Endpoint-2?
Community Votes
50% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The core concept tested is ACI's default behavior for intra-EPG traffic, specifically the requirement of Unicast Routing for inter-leaf communication.
This question addresses how to resolve Layer 2 connectivity issues between endpoints in the same EPG but different Bridge Domains in Cisco ACI. It establishes that enabling Unicast Routing on the Bridge Domain is the correct configuration.
Many learners incorrectly select 'Configure a contract' (B) because they overgeneralize ACI's strict policy model, failing to realize contracts are not needed for same-EPG traffic.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
In Cisco ACI, endpoints in the same EPG communicate via flooding or hardware proxying by default. However, when endpoints are attached to different leaf switches (Leaf-101 and Leaf-102), direct Layer 2 forwarding may fail if the fabric relies on routing or specific proxy settings. Enabling 'Unicast Routing' on the Bridge Domain allows the fabric to route traffic between the endpoints using the BD's subnet, ensuring connectivity across the spine.Why the Other Options Are Wrong
Option B is incorrect because contracts enforce communication between different EPGs; same-EPG traffic is allowed by default. Option A ('Hardware Proxy') is typically used for ARP/ND optimization, not primary L2/L3 reachability. Option D ('Silent Host Detection') helps with DHCP learning but does not solve basic IP reachability.Community Comment Notes
Commenters like prospio971 correctly identify that 'Unicast Routing' is the key missing feature, as noted in their explanation about Layer 3 routing between endpoints. Another user mentions silent host detection, which is less relevant than the routing configuration for this specific failure mode.Exam Strategy
When troubleshooting ACI connectivity, always check if the Bridge Domain has Unicast Routing enabled if endpoints cannot reach each other across leaves. Remember that same-EPG traffic does not require contracts.
Frequently Asked Questions
Why isn't a contract needed for same-EPG communication?
Contracts only restrict traffic between different EPGs. Traffic within the same EPG is permitted by default.
Does Unicast Routing affect Layer 2 traffic?
It enables Layer 3 routing capabilities within the Bridge Domain, allowing the fabric to route packets between subnets or endpoints if L2 forwarding fails.