OSPF Design Considerations: Designing a Stable and Scalable OSPF Domain, Summaries of Network Design

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OSPF Design Considerations

D E S I G N I N G A S T A B L E A N D S C A L A B L E O S P F D O M A I N

OSPF Design

• (^) Designed for hierarchical networks
  • (^) Requires a lot more understanding and planning than EIGRP
    • (^) Concept of hub and spoke topology is deeply rooted with backbone area requirement
• (^) Can operate over NBMA networks

OSPF Design Recommendations

• (^) Neighboring routers: 60 or less
  • (^) Routers in a single area: 50 or less
    • (^) Areas connected to a single ABR: up to 3
      • (^) Use the most powerful router as the DR
  • (^) Use contiguous split-able addressing Images courtesy of Ciscopress.com

OSPF Area Design

• (^) In a hub-and-spoke topology for a branch office, keep the area boundary on the hub side.
• (^) Keep branches in their own separate area to avoid flooding LSAs over the WAN Images courtesy of Ciscopress.com

Scaling OSPF

• (^) Keep Area 0 small, clean, and stable
  • Some large networks will only have ABRs in area 0
• (^) Use contiguous, split-able addressing where possible
• (^) Design areas around functional or geographic boundaries

OSPFv

• (^) Effectively the same as OSPFv2 but is used for IPv
• (^) Continues to use an IPv4 format Router ID
• (^) Same design principles apply to OSPFv3 as OSPFv

Q&A Which type of area should you use in an enterprise OSPF deployment if you want to prevent the propagation of type 5 LSAs but still allow the redistribution of external routes? A. Stub B. Total Stub C. NSSA D. Backbone