352-001 · Question #128
Which two OSPF design considerations should you implement to support the eventual growth of a network, so that CPU and memory are unaffected by the size and complexity of the link-state database in…
The correct answer is C. Turn on the Incremental SPF feature. E. Turn on packet pacing. Incremental SPF limits CPU usage by recalculating only the changed portion of the SPF tree, while packet pacing throttles OSPF update bursts so the CPU is not overwhelmed regardless of LSDB size.
Question
Which two OSPF design considerations should you implement to support the eventual growth of a network, so that CPU and memory are unaffected by the size and complexity of the link-state database in a large service provider network? (Choose two.)
Options
- ATurn on route dampening.
- BCreate network summaries.
- CTurn on the Incremental SPF feature.
- DAdd more memory.
- ETurn on packet pacing.
- FAdd redundancy between critical locations.
How the community answered
(25 responses)- A8% (2)
- B4% (1)
- C44% (11)
- D16% (4)
- F28% (7)
Why each option
Incremental SPF limits CPU usage by recalculating only the changed portion of the SPF tree, while packet pacing throttles OSPF update bursts so the CPU is not overwhelmed regardless of LSDB size.
Route dampening is a BGP feature for suppressing unstable prefixes; it has no equivalent in OSPF and does not affect LSDB processing.
Network summaries reduce the number of LSAs exchanged but represent a topology design decision, not a feature that makes CPU and memory resilient to LSDB growth in an already large network.
Incremental SPF (iSPF) recomputes only the subtree affected by a topology change rather than the full shortest-path tree, keeping CPU consumption proportional to the change rather than to the total LSDB size.
Adding memory addresses the symptom rather than the design; it does not prevent CPU or memory from being stressed as the network grows.
OSPF packet pacing spreads LSA retransmissions and flooding over time, preventing large bursts that would spike CPU and memory usage when the LSDB is large or highly dynamic.
Adding redundancy improves availability but increases the number of LSAs and adjacencies, potentially making CPU and memory consumption worse.
Concept tested: OSPF iSPF and packet pacing for scalable SP design
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-16/iro-ospf-xe-16-book/iro-ospf-isf.html
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