You are designing an overlay solution for two Data Centers based on the Aruba CX platform. Each Data Center has two rooms and each room is its own fabric. What is the underlay routing protocol run…

Question

Options

• AiBGP
• BeBGP
• COSPF
• DIS-IS

• A
  3% (1)
• B
  6% (2)
• C
  82% (28)
• D
  9% (3)

Explanation

OSPF (C) is the correct underlay routing protocol within each room/fabric in Aruba CX Data Center designs. In the Aruba reference architecture, OSPF distributes loopback reachability between leaf and spine switches within a fabric, enabling the VXLAN tunnels that form the overlay.

Why the distractors are wrong:

• A (iBGP) and B (eBGP) - BGP operates at the overlay layer (EVPN control plane), not the underlay. BGP is used between fabrics or DCs to exchange MAC/IP routes over the VXLAN fabric, not to establish basic IP reachability within a room.
• D (IS-IS) - While IS-IS is a valid IGP used in some vendor implementations (notably Juniper/Nokia), it is not part of the Aruba CX reference architecture; OSPF is Aruba's prescribed underlay IGP.

Memory tip: Think of it as two layers - the underlay is the foundation (OSPF builds the IP roads between switches within the room), and the overlay rides on top (BGP/EVPN carries the tenant traffic across those roads). When Aruba says "within a fabric," that's always the OSPF layer.

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