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Multiarea OSPF CCNP 1: Advanced Routing Chapter 5.

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Presentation on theme: "Multiarea OSPF CCNP 1: Advanced Routing Chapter 5."— Presentation transcript:

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2 Multiarea OSPF CCNP 1: Advanced Routing Chapter 5

3 Overview 1.OSPF Review 2.Multiarea OSPF Operation and Configuration 3.Area Types: Stub, Totally Stub, and NSSA 4.Virtual Links 5.Monitoring and Verifying Multiarea OSPF 6.OSPF Pitfalls: “ What could possibly go wrong? ”

4 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

5 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.

6 OSPF Features Scalability OSPF is considered by most to be the 2 nd 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

7 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

8 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?

9 What problem are you trying to solve? 5.1.1

10 What problem are you trying to solve? 5.1.1

11 OSPF Areas 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

12 OSPF Areas 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

13 Configuration R1(config)#router ospf 1 R1(config-router)#network area 0 R1(config-router)#network area 10 R1(config-router)#network area 1 What kind of router is R1? InternalBackboneABRASBR Area 10 Area 1 Area 0

14 Configuration R1(config)#router ospf 1 R1(config-router)#network area 0 R1(config-router)#network area 10 R1(config-router)#network area 1 What kind of router is R1? BackboneABR Area 10 Area 1 Area 0

15 Configuration R2(config)#router ospf 1 R2(config-router)#network area 0 R2(config-router)#network area 0 R2(config-router)#network area 0 What kind of router is R2? InternalBackboneABRASBR

16 Configuration R2(config)#router ospf 1 R2(config-router)#network area 0 R2(config-router)#network area 0 R2(config-router)#network area 0 What kind of router is R2? InternalBackbone Look Ma, no diagram!

17 Configuration R3(config)#router ospf 1 R3(config-router)#network area 10 R3(config-router)#network area 10 R3(config-router)#network area 10 What kind of router is R3? InternalBackboneABRASBR

18 Configuration R3(config)#router ospf 1 R3(config-router)#network area 10 R3(config-router)#network area 10 R3(config-router)#network area 10 What kind of router is R3? Internal

19 Configuration R4(config)#ip route serial 0/0 R4(config)#router ospf 1 R4(config-router)#network area 0 R4(config-router)#network area 10 R4(config-router)#network area 10 R4(config-router)#redistribute static What kind of router is R4? InternalBackboneABRASBR

20 Configuration R4(config)#ip route serial 0/0 R4(config)#router ospf 1 R4(config-router)#network area 0 R4(config-router)#network area 10 R4(config-router)#network area 10 R4(config-router)#redistribute static What kind of router is R4? BackboneABRASBR

21 Configuration R5(config)#router ospf 1 R5(config-router)#network area 1 R5(config-router)#network area 10 R5(config-router)#network area 10 What kind of router is R5? InternalBackboneABRASBR

22 Configuration R5(config)#router ospf 1 R5(config-router)#network area 1 R5(config-router)#network area 10 R5(config-router)#network area 10 What kind of router is R5? InternalBackboneABRASBR Every area MUST have at least one link in Area 0. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

23 OSPF LSA Types

24 LSA Types and Routing tables R1#show ip route ospf O /8 [110/65] via , 00:04:23, Serial 0/0 O IA /8 [110/65] via , 00:04:23, Serial 0/0 O E /8 [110/65] via , 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

25 OSPF Stub Areas 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.

26 Stub Areas and LSAs 5.2.2

27 Stub vs. Totally Stub 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

28 Stub and Totally Stub Configuration 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

29 NSSA 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

30 NSSA Configuration 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

31 Stub and NSSA 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

32 Summarizing with OSPF 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 ASBR: R1(config-router)#summary-address

33 Breaking the Area 0 Rule 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

34 OSPF Virtual Links R1(config-router)#area 1 virtual-link R3(config-router)#area 1 virtual-link 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.

35 OSPF Pitfalls OSPF Path Selection OSPF over NBMA OSPF over DDR

36 Multiarea OSPF CCNP 1: Advanced Routing Chapter 5


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