Which action is needed on a Cisco UCS to make ACI dynamic discovery work?

Question

Options

• AEnable VLAN grouping on the fabric interconnect uplinks.
• BEnable the Cisco Discovery Policy on the Cisco UCSM VNICs
• CForward the infrastructure VLAN toward the ESX.
• DUse MTU 9000.

• A
  9% (3)
• C
  6% (2)
• D
  84% (27)

Explanation

MTU 9000 (jumbo frames) must be enabled on the Cisco UCS Fabric Interconnect uplinks because ACI's infrastructure VLAN traffic uses VXLAN encapsulation, which adds ~50 bytes of overhead per frame. Without jumbo frames, VXLAN-encapsulated packets used during dynamic discovery (LLDP/DHCP over the infra VLAN) get dropped or fragmented, preventing the APIC from discovering connected devices.

Why the distractors are wrong:

• A - VLAN grouping on uplinks is a UCS port channel concept unrelated to ACI discovery requirements.
• B - There is no "Cisco Discovery Policy" requirement specifically on VNICs for ACI dynamic discovery; LLDP is handled at the fabric interconnect level, not per-VNIC.
• C - The ACI infrastructure VLAN is intentionally not extended to ESX hosts in a standard deployment; it stays between the Fabric Interconnects and ACI leaf switches.

Memory tip: Think "VXLAN = eXtra bytes = need eXtra MTU." ACI uses VXLAN on its infra VLAN, so anywhere that traffic flows - including UCS uplinks - must support jumbo frames (9000 MTU) or discovery silently fails.

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