Exam 400-007 topic 1 question 50 discussion

In an OSPF network with routers connected together with Ethernet cabling, the topology that typically takes the longest to converge is the ring topology (option B). In a ring topology, there is only one path available between any two routers, and when a link fails, the OSPF routers need to recalculate the routes, which can introduce delays in the convergence process. The other options listed (squared, partial mesh, triangulated, full mesh) typically provide multiple paths between routers, which can help in faster convergence by allowing alternative routes to be used when a link fails.

In an OSPF network, convergence time depends on the number of adjacencies that must be formed and the number of LSAs (Link-State Advertisements) that must be exchanged and processed. Full mesh means that every router is connected to every other router. This results in O(n²) adjacencies, where n is the number of routers. Each router must exchange LSAs with every other router, leading to high CPU and memory usage. As the network scales, the number of LSAs increases exponentially, making full mesh the slowest topology to converge.

Answer: E https://learningnetwork.cisco.com/s/question/0D53i00000M0a29CAB/ospf-convergence-and- typologies

A square is basically a ring with 4 nodes, no difference. More links, bigger tree to calculate the shorter path. f

Answer C: Partial mesh topologies can result in longer convergence times due to their irregular and less predictable connectivity patterns, which make it more complex for OSPF to quickly recompute optimal paths and achieve a consistent network state across all routers.

Should be E "full mesh" which takes the most links ! so it will take more time on the SPF calculation !

Guys It B Ring. Dont look for crappy answers

Ring has no OSPF DR/BDR election, whereas full-mesh broadcast multiaccess has DR/BDR election; not exactly sure what is the delay in DR/BDR election process besides LSA exchanges and building LSDB. Ring (SONET is a ring as well) must be OSPF point-to-point network; on a ptp network OSPF converge faster.

Convergence of the ring topologies are generally slow compared to other alternatives such as partial mesh, full-mesh and diverge planes topologies. https://packetpushers.net/network-topologies/

B seems correct because in Ring topology each router first needs to exchange LSAs with its 2 direct and other neighbors and this will continue until all neighbors sync up their LSDB

I vote for B as the LSA will take longer to propagate. Think of a ring of 12 routers

It should be E

Answer should be C