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352-001 · Question #563
352-001 Question #563: Real Exam Question with Answer & Explanation
The correct answer is B: Ring. In an OSPF network of 20 Ethernet-connected routers, a ring topology takes the longest to converge because LSAs must propagate around the entire ring and only a single alternate path exists after a failure.
Question
In an OSPF network with 20 routers connected together with Ethernet cabling , which topology typically takes the longest to converge?
Options
- AFull mesh
- BRing
- CSquared
- DTriangulated
- EPartial mesh
Explanation
In an OSPF network of 20 Ethernet-connected routers, a ring topology takes the longest to converge because LSAs must propagate around the entire ring and only a single alternate path exists after a failure.
Common mistakes.
- A. Full mesh provides direct adjacencies between all routers, so LSAs spread immediately to all neighbors and convergence is extremely fast.
- C. A squared (grid) topology is not standard OSPF terminology, but a grid provides multiple equal-cost paths that reduce convergence time compared to a ring.
- D. A triangulated topology implies multiple triangular redundant paths, giving routers more next-hop options and faster SPF recalculation.
- E. A partial mesh still provides more redundant links than a ring, reducing the flood diameter and convergence time.
Concept tested. OSPF convergence time vs. network topology
Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html
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