{OSPF Study Areas: Stub, Totally Stub, Not-So-Stub, and Totally Not-So-Stub}

Introduction

• Presenter: Rohit Pardo Sonny
• Certifications: 5 CCIEs (Route/Switch, Security, Voice, Collaboration, Service Provider)
• Focus: OSPF Study Areas and LSA Types

Topics Covered

1. LSA Types Overview
2. Stub Areas
3. Totally Stub Areas
4. Not-So-Stub Areas
5. Totally Not-So-Stub Areas
6. Lab Demonstration

LSA Types

• LSDB (Link State Database): Backbone of OSPF containing LSAs.
• Key LSA Types Discussed:
  • LSA 1 (Router LSA): Prefix information within the same area, contains router interfaces and costs.
  • LSA 2 (Network LSA): Generated by DR in broadcast networks, lists all routers in the broadcast domain.
  • LSA 3 (Summary LSA): Generated by ABR, represents inter-area routes.
  • LSA 4 (ASBR Summary LSA): Router ID of ASBRs, generated by ABRs.
  • LSA 5 (External LSA): External routes redistributed into OSPF, generated by ASBRs.
  • LSA 7 (NSSA External LSA): Used in NSSA for external routes, translated to LSA 5 by ABRs.

Stub Areas

• Purpose: Reduce size of routing tables and processing for routers with limited resources.
• Key Rules: Cannot be Area 0, cannot include virtual links or ASBRs.
• Effect: Blocks LSA 5 and LSA 4, ABR advertises a default route (Type 3) into the stub area.
• Configuration: area <ID> stub
• Verification: Reduced routing table and LSDB without external LSAs.

Totally Stub Areas

• Purpose: Further reduce routing table size by blocking inter-area routes.
• Key Rules: Same as stub areas.
• Effect: Blocks LSA 5, LSA 4, and LSA 3. ABR advertises only a single default route (Type 3).
• Configuration: area <ID> stub no-summary on ABR.
• Verification: Minimal routing table with intra-area routes and one default route.

Not-So-Stub Areas (NSSA)

• Purpose: Allows ASBR in an area for external routes while still reducing routing analytics.
• Key Rules: Cannot be Area 0 or include virtual links, ASBR allowed.
• Effect: External routes advertised as LSA 7 within NSSA, ABR translates to LSA 5.
• Configuration: area <ID> nssa
• Optional Command: nssa default-information originate to generate default route.
• Verification: LSA 7 within NSSA, translated to LSA 5 by ABR.

Totally Not-So-Stub Areas

• Purpose: Combination of NSSA and Totally Stub, further restricting inter-area routes.
• Effect: Blocks LSA 5, LSA 4, and LSA 3. Generates a default route automatically (Type 3).
• Configuration: area <ID> nssa no-summary on ABR.
• Verification: Default route present, reduced routing table and LSDB.

Lab Demonstration

1. Initial Setup Confirmation: OSPF Multi-Area.
2. Implementation Steps:
   • Convert Area 3 to Stub Area.
   • Verify LSA 5 and LSA 4 blocking, default route generation in stub area.
   • Convert to Totally Stub, verify LSA 3 blocking.
   • Configure NSSA in Area 2, translate-type 7 to 5.
   • Convert NSSA to Totally Not-So-Stub, verify routing table reduction, automatic default route.

Conclusion

• Summary: Overview of configuring and verifying different OSPF study areas.
• Questions and Thanks: Interactive Q&A and gratitude for attendance.