CCNA Advance

Chapter 3OSPF Multi Area part2

OSPF Route Summarization

3Benefits of Route Summarization

Minimizes number of routing table entries Localizes impact of a topology change Reduces LSA type 3 and 5 flooding and saves CPUresources

4Using Route Summarization

Inter-area summary link carries mask. One or more entries can represent several subnets.

5Interarea Route Summarization on an ABR

6Route Summarization Configuration Exampleat ABR

7External Route Summarization on an ASBR

8Route Summarization Configuration Exampleat ASBR

9Default Routes in OSPF

A default route is injected into OSPF as an external LSA type 5. Default route distribution is not on by default; use the default-information originate command under the OSPF routing process.

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Configuring OSPF Default Routes

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Default Route Configuration Example

Configuring OSPF Special Area Types

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Types of Areas

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Stub and Totally Stub Area Rules

An area can be stub or totally stub if: There is a single ABR (single exit point), or if there is more than one ABR, suboptimal routing paths to other areas or external autonomous systems are acceptable. All routers in the area are configured as stub routers. There is no ASBR in the area. The area is not backbone area (area 0) No virtual links go through the area. Stub areas will result in memory and processing savingsdepending upon the size of the network.

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Using Stub Area Receives all routes fromwithin A.S: Within the local area - LSA 1s and LSA 2s (if appropriate) From other areas (Inter-Area) - LSA 3s Does not receive routes from External A.S (External Routes). ABR: Default route isautomatically injected into stubarea by ABR ABR blocks all LSA 4sand LSA 5s. If LSA 5s are not knowninside an area, LSA 4sare not necessary. LSA 3s are propagatedby the ABR.

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Using Stub Area

ASBR

ABR-1 ABR-2

InternalArea 51

Area 1

Area 0

172.16.0.0/16

172.16.1.0/24

172.16.51.0/24172.16.10.4/30

172.16.20.0/24

10.1.0.0/24

11.0.0.0/812.0.0.0/813.0.0.0/8

.1

.1

.2 .3

.5

.6

.1

Lo - RouterID192.168.2.1/32

Lo - RouterID192.168.1.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

Lo - RouterID192.168.4.1/32

LSA1, 2LSA 4

LSA 5XLSA 3

Stub Area

Default route

LSA 3s (Inter-Area routes) are propagated by the ABR. ABR blocks all LSA 4s (reachabilitly to ASBR) and LSA 5s (External routes) The ABR injects a default route into the stub area, pointing to the ABR. (This does notmean the ABR has a default route of its own.)

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Stub Areas - Database

Notice that there are no LSA 4s or LSA 5s for stub area routers. Default Route injected by ABR (LSA 3)

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Stub Areas Routing table

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Stub Area Configuration

This command turns on stub area networking. All routers in a stub area must use the stub command.

This command defines the cost of a default route sent into the stub area. The default cost is 1.

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OSPF Stub Area Configuration Example

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Using Totally Stubby Areas

Receives routes from within A.S: Only from within the local area - LSA 1s and LSA 2s (if appropriate) Does not receive routes from other areas (Inter-Area) - LSA 3s Does not receive routes from External AS (External Routes) ABR: ABR blocks all LSA 4s and LSA 5s. ABR blocks all LSA 3s, except propagating a default route. Default route is automatically injected into totally stubby area byABR. Routing tableis reduced to a minimum. All routers must be configured as stub. ABR must be configured as totally stubby. This is a Ciscos proprietary feature

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Totally Stubby Areas - Database

Default route is injected into totally stubby area by ABR for all other networks (inter-area and external routes) Does not receive routes from other areas (Inter-Area) Does not receive routes from External A.S. (External Routes)

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Totally Stubby Areas Routing table

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Totally Stubby Areas ABR RTable

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Totally Stubby Configuration

The addition of no-summary on the ABR creates a totally stubbyarea and prevents all summary LSAs from entering the stubArea configure on ABR

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Totally Stubby Configuration Example

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Not-So-Stubby Areas

NSSA breaks stub arearules. ASBR (R1) is allowed inNSSA. Special LSA type 7(routing table 0 N1 or 0 N2)defined, sent by ASBR.

ABR (R2) converts LSA type 7to LSA type 5. ABR sends default route into NSSAinstead of external routes from otherASBRs (manual configuration, notautomatically). NSSA is an RFC addendum.

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Example: NSSA Configuration

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NSSA Totally Stubby Configuration

NSSA totally stubby area is a Cisco proprietary feature.

Configuring OSPF Authentication

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OSPF Authentication Types

OSPF supports 2 types of authentication: Simple password (or plain text) authentication MD5 authentication Router generates and checks every OSPF packet. Router authenticates the source of each routing update packet that it receives. Configure a key (password); each participating neighbor must have same key configured.

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Example Simple Password AuthenticationConfiguration

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Example MD5 Authentication Configuration

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Summary

OSPF is an open-standard link-state routing protocol, offering quick convergence and the ability to scale large networks. There are five OSPF packet types: hello, DBD, LSU, LSR, and LSAck. Configuration of OSPF is a two-step process: Enter OSPF configuration with the router ospf command. Use the network command to describe which interfaces will run OSPF in which area. OSPF defines three types of networks: point-to-point, broadcast, and NBMA. On NBMA networks, OSPF mode options include nonbroadcast, broadcast, point-tomultipoint, point-to-multipoint nonbroadcast, and point-to-point. LSAs are the building blocks of the LSDB. There are 11 types of OSPF LSAs. Route summarization reduces OSPF LSA flooding and routing table size, whichreduces memory and CPU utilization on routers. Stub area techniques improve OSPF performance by reducing the LSA flooding. OSPF supports two types of authentication: Simple password (or plain text) authentication MD5 authentication

Question ?

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CCNA AdvanceOSPF Route SummarizationBenefits of Route SummarizationUsing Route SummarizationInterarea Route Summarization on an ABRRoute Summarization Configuration Exampleat ABRExternal Route Summarization on an ASBRRoute Summarization Configuration Exampleat ASBRDefault Routes in OSPFConfiguring OSPF Default RoutesDefault Route Configuration ExampleConfiguring OSPF Special Area TypesTypes of AreasStub and Totally Stub Area RulesUsing Stub AreaUsing Stub AreaStub Areas - DatabaseStub Areas Routing tableStub Area ConfigurationOSPF Stub Area Configuration ExampleUsing Totally Stubby AreasTotally Stubby Areas - DatabaseTotally Stubby Areas Routing tableTotally Stubby Areas ABR RTableTotally Stubby ConfigurationTotally Stubby Configuration ExampleNot-So-Stubby AreasExample: NSSA ConfigurationNSSA Totally Stubby ConfigurationConfiguring OSPF AuthenticationOSPF Authentication TypesExample Simple Password AuthenticationConfigurationExample MD5 Authentication ConfigurationSummaryQuestion ?