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Multiarea OSPF

Multiarea OSPF. CCNP 1: Advanced Routing Chapter 5. Overview. OSPF Review Multiarea OSPF Operation and Configuration Area Types: Stub, Totally Stub, and NSSA Virtual Links Monitoring and Verifying Multiarea OSPF OSPF Pitfalls: “ What could possibly go wrong? ”. Open Shortest Path First.

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Multiarea OSPF

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  1. Multiarea OSPF CCNP 1: Advanced Routing Chapter 5

  2. Overview • OSPF Review • Multiarea OSPF Operation and Configuration • Area Types: Stub, Totally Stub, and NSSA • Virtual Links • Monitoring and Verifying Multiarea OSPF • OSPF Pitfalls: “What could possibly go wrong?”

  3. Open Shortest Path First • OSPF is a scalable link-state protocol that determines the best path between two networks by comparing the aggregate costs of all possible paths. • Extremely scalable • Sends incremental updates • Establishes a relationship between neighbor routers • Hierarchical • Supports VLSM

  4. The OSPF Database • Each OSPF-enabled interface is considered a “link”. • All links are assimilated into the SPF database. • show ip ospf database • You too will be assimilated into the collective. Resistance is futile. http://www.routergod.com/sevenofnine

  5. OSPF Features • Scalability • OSPF is considered by most to be the 2nd most scalable IP IGP • OSPF is used in both Service Provider and Enterprise networks • Incremental Updates • Fast convergence time • Light on bandwidth • Heavy on router CPU cycles

  6. OSPF Neighbor Relationships • Point-to-point links: OSPF detects and connects to neighboring OSPF routers, and the routers exchange link state databases. • Multiaccess links: OSPF detects and connects to neighboring OSPF routers. A designated Router (DR) and Backup Designated Router (BDR) are elected. The routers exchange link state databases with the DR, and their tables are also sent to the BDR. • Verification/Troubleshooting: • Router#show ip ospf neighbors • If you don’t see a DR, guess what? • For added fun: • Router(config)#alias exec sion show ip ospf neighbors

  7. Hierarchy • OSPF is based on a 2-layer hierarchy • Backbone and Non-backbone • An OSPF domain can be divided in areas • Each area has its own link state database • Why?

  8. 5.1.1 What problem are you trying to solve?

  9. 5.1.1 What problem are you trying to solve?

  10. An area can contain as many as “50ish” routers This number varies, based on the number and stability of links and the resources on the routers Backbone area should be relatively small Backbone area should consist of stable links Backbone Area = Area 0 = Teh Princess OSPF Areas

  11. Backbone Router: Router with at least one interface in Area 0 Internal Router: Router with all interfaces in the same area Area Border Router (ABR): Router with interfaces in two or more different areas Autonomous System Boundary Router (ASBR): Router with at least one interface connected to a non-OSPF domain OSPF Areas

  12. R1(config)#router ospf 1 R1(config-router)#network 10.3.0.0 0.0.255.255 area 0 R1(config-router)#network 10.1.0.0 0.0.255.255 area 10 R1(config-router)#network 10.2.0.0 0.0.255.255 area 1 What kind of router is R1? Internal Backbone ABR ASBR Configuration Area 1 Area 10 Area 0

  13. R1(config)#router ospf 1 R1(config-router)#network 10.3.0.0 0.0.255.255 area 0 R1(config-router)#network 10.1.0.0 0.0.255.255 area 10 R1(config-router)#network 10.2.0.0 0.0.255.255 area 1 What kind of router is R1? Backbone ABR Configuration Area 1 Area 10 Area 0

  14. R2(config)#router ospf 1 R2(config-router)#network 10.3.0.0 0.0.255.255 area 0 R2(config-router)#network 10.1.0.0 0.0.255.255 area 0 R2(config-router)#network 10.2.0.0 0.0.255.255 area 0 What kind of router is R2? Internal Backbone ABR ASBR Configuration

  15. R2(config)#router ospf 1 R2(config-router)#network 10.3.0.0 0.0.255.255 area 0 R2(config-router)#network 10.1.0.0 0.0.255.255 area 0 R2(config-router)#network 10.2.0.0 0.0.255.255 area 0 What kind of router is R2? Internal Backbone Look Ma, no diagram! Configuration

  16. R3(config)#router ospf 1 R3(config-router)#network 10.3.0.0 0.0.255.255 area 10 R3(config-router)#network 10.1.0.0 0.0.255.255 area 10 R3(config-router)#network 10.2.0.0 0.0.255.255 area 10 What kind of router is R3? Internal Backbone ABR ASBR Configuration

  17. R3(config)#router ospf 1 R3(config-router)#network 10.3.0.0 0.0.255.255 area 10 R3(config-router)#network 10.1.0.0 0.0.255.255 area 10 R3(config-router)#network 10.2.0.0 0.0.255.255 area 10 What kind of router is R3? Internal Configuration

  18. R4(config)#ip route 10.4.0.0 255.255.0.0 serial 0/0 R4(config)#router ospf 1 R4(config-router)#network 10.3.0.0 0.0.255.255 area 0 R4(config-router)#network 10.1.0.0 0.0.255.255 area 10 R4(config-router)#network 10.2.0.0 0.0.255.255 area 10 R4(config-router)#redistribute static What kind of router is R4? Internal Backbone ABR ASBR Configuration

  19. R4(config)#ip route 10.4.0.0 255.255.0.0 serial 0/0 R4(config)#router ospf 1 R4(config-router)#network 10.3.0.0 0.0.255.255 area 0 R4(config-router)#network 10.1.0.0 0.0.255.255 area 10 R4(config-router)#network 10.2.0.0 0.0.255.255 area 10 R4(config-router)#redistribute static What kind of router is R4? Backbone ABR ASBR Configuration

  20. R5(config)#router ospf 1 R5(config-router)#network 10.3.0.0 0.0.255.255 area 1 R5(config-router)#network 10.1.0.0 0.0.255.255 area 10 R5(config-router)#network 10.2.0.0 0.0.255.255 area 10 What kind of router is R5? Internal Backbone ABR ASBR Configuration

  21. R5(config)#router ospf 1 R5(config-router)#network 10.3.0.0 0.0.255.255 area 1 R5(config-router)#network 10.1.0.0 0.0.255.255 area 10 R5(config-router)#network 10.2.0.0 0.0.255.255 area 10 What kind of router is R5? Internal Backbone ABR ASBR Every area MUST have at least one link in Area 0. Configuration XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

  22. OSPFLSA Types

  23. LSA Types and Routing tables R1#show ip route ospf O 6.0.0.0/8 [110/65] via 5.0.0.2, 00:04:23, Serial 0/0 O IA 7.0.0.0/8 [110/65] via 5.0.0.2, 00:04:23, Serial 0/0 O E2 8.0.0.0/8 [110/65] via 5.0.0.2, 00:04:23, Serial 0/0 Type 2: O Type 3: O IA (How to reach ABRs) Type 4: O IA (How to reach ASBRs) Type 5: O E1 or O E2

  24. A stub area has only one entry and exit point. Topology changes in other areas do not affect stub areas. The ABR is still the only way out. OSPF Stub Areas

  25. Stub Areas and LSAs 5.2.2

  26. Similarities ABR does not advertise Type 4 or 5 LSAs into the area There should be no OE1 or OE2 routes in the area ABR advertises a default route to the internal routers Neither area can have an ASBR in it Neither area can be the backbone Differences Totally stub does not advertise Type 3 LSAs either Stub routing table: O,O IA, and default route Totally stub routing table: O and default route Stub vs. Totally Stub

  27. Stub Area R1(config-router)#area 1 stub R2(config-router)#area 1 stub Command must be entered on all routers in the area Totally Stubby Area R1(config-router)#area 1 stub no-summary R2(config-router)#area 1 stub ABR is configured with stub no-summary Internal routers are configured with stub 5.4.3 Stub and Totally Stub Configuration

  28. Many service providers have OSPF areas that have only one exit point, but the areas contain an ASBR Solution: Not-So-Stubby Areas (NSSAs) The ASBR originates a Type 7 LSA The ABR converts from Type 7 to Type 5 NSSA

  29. Not-So-Stubby Area R1(config-router)#area 1 nssa R2(config-router)#area 1 nssa R2(config-router)#redistribute static Command must be entered on all routers in the area ASBR must be configured to inject non-OSPF routes Totally Not-So-Stubby Area R1(config-router)#area 1 nssa no-summary R2(config-router)#area 1 stub ABR is configured with nssa no-summary Internal routers are configured with nssa NSSA Configuration

  30. By default, stub ABRs advertise a default route. By default, NSSA ABRs do not. To force an NSSA to advertise a default route: R1(config-router)#area 1 nssa default-information-originate 5.6.3 Stub and NSSA

  31. Only ABRs and ASBRs can summarize Routes should be summarized as/before they are advertised to Area 0 ABR: R1(config-router)#area 1 range 10.0.0.0 255.0.0.0 ASBR: R1(config-router)#summary-address 10.0.0.0 255.0.0.0 5.3.2 Summarizing with OSPF

  32. Every area must have at least one interface on at least one router in Area 0. Area 0 must be contiguous. Problem: Mergers Problem: ExtraNets 5.5.1 Breaking the Area 0 Rule

  33. R1(config-router)#area 1 virtual-link 3.3.3.3 R3(config-router)#area 1 virtual-link 1.1.1.1 Virtual links are established by router IDs Can be used to join a discontiguous Area 0 Can be used to “tunnel” a remote area to Area 0 Note: YOU SHOULD NOT FIND YOURSELF IN THIS SITUATION. OSPF Virtual Links

  34. OSPF Path Selection OSPF over NBMA OSPF over DDR OSPF Pitfalls

  35. Multiarea OSPF CCNP 1: Advanced Routing Chapter 5

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