In L3 Spine and Leaf design OSPF routing, which switches can be ABRs and connect your network to a WAN provider?

Question

Options

• ALeaf switches that act as centralized routers for the overlay
• BLeaf switches that act as distributed routers for the overlay
• CSpine switches
• DBorder leaf switches

• A
  8% (3)
• B
  3% (1)
• C
  3% (1)
• D
  88% (35)

Explanation

Border leaf switches (D) are purpose-built to sit at the edge of the spine-leaf fabric and connect to external networks like WAN providers or other data centers. In OSPF terms, they act as ABRs (Area Border Routers) because they bridge the internal fabric OSPF area and the external/backbone area - exactly the role an ABR is designed to fill.

Why the distractors are wrong:

• A (centralized router leaf switches) - these handle overlay routing for internal traffic between endpoints, not external WAN connectivity.
• B (distributed router leaf switches) - similarly, distributed routing leaf switches serve the internal overlay; they don't have the external-facing uplinks needed for WAN.
• C (spine switches) - spines provide high-speed east-west interconnection within the fabric between leaf switches; they are not designed or positioned to peer with external WAN providers.

Memory tip: Think of "Border Leaf" literally - the word border signals the boundary of your network. Just as a country's border crossing is where you leave domestic territory, a border leaf is where traffic leaves the internal fabric and enters the external WAN world, making it the natural ABR candidate.

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