Module 3- Stub, Totally Stubby, and Not-So-Stubby Areas pptx

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BSCI Module 3 Lesson 7 - Stub, Totally Stubby,
and Not-So-Stubby Areas
OSPF
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Objective
 Configuring OSPF Area Types
 Using Stub and Totally Stubby Areas
 Configuring Stub Area
 OSPF Stub Area Configuration Example
 Configuring Totally Stub Areas
 Totally Stubby Area Configuration Example
 Interpreting Routing Tables
 Configuring Not-So-Stubby Areas
 Configuring Not-So-Stubby Area Example
 Configuring an NSSA Totally Stubby Area Example
 Verifying All Stub Area Types
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Configuring OSPF Area Types
 Standard area: Accepts link updates, route summaries,
and external routes (the default).
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Configuring OSPF Area Types
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Using Stub and Totally Stubby Areas
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Stub Area
 A stub area is an area into which AS External LSAs are not flooded.
And if type 5 LSAs are not known inside an area, type 4 LSAs are
unnecessary; these LSAs are also blocked
 As in any area, all routers in a stub area must have identical link-
state databases. To ensure this condition, all stub routers will set a
flag (the E-bit) in their Hello packets to zero.
 No router within a stub area can be an ASBR.
 Virtual links cannot be configured within, nor transit, a stub area.
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Configuring Stub Area
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OSPF Stub Area Configuration Example

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Totally Stub Areas
 The totally stubby area is a Cisco proprietary enhancement that
further reduces the number of routes in the routing table.
 A totally stubby area blocks external type 5 LSAs and summary
type 3 and 4 LSAs (interarea routes) from entering the area.
 Totally stubby areas use a default route to reach not only
destinations external to the autonomous system but also all
destinations external to the area.
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Configuring Totally Stub Areas
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Totally Stubby Area Configuration Example
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Interpreting Routing Tables
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Configuring Not-So-Stubby Areas
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Configuring Not-So-Stubby Areas
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Configuring Not-So-Stubby Areas
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Configuring Not-So-Stubby Area Example
 To cause router 2 (the NSSA ABR) to generate an O
*N2 default route (O *N2 0.0.0.0/0) into the NSSA, use
the default-information-originate option of the area
area-id nssa command on router 2.
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Configuring an NSSA Totally Stubby Area
Example
 A single default route replaces both inbound-external (type 5)
LSAs and summary (type 3 and 4) LSAs into the area.The NSSA
ABR, which is router 2, automatically generates the O *N2 default

route into the NSSA area with the no-summary option configured
at the ABR, so the default-information-originate option is not
required.
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Verifying All Stub Area Types
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Area Type
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Activity
 3.7.1 Drag and Drop: ID the Area
–Upon completion of this activity, the student will be able to
identify the difference between stub and totally stubby areas in
OSPF.
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Self Check
1. Stub vs Totally Stub
2. NSSA vs totally NSSA
3. How to advertise default-route into NSSA

4. How to use default-cost for advertise 0.0.0.0/0
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Summary
 Stub
 Stub summary
 NSSA
 NSSA summary
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Q and A
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Resources
 How Does OSPF Generate Default Routes?
– />e09186a0080094a74.shtml
 OSPF Not-So-Stubby Area (NSSA)
– />e09186a0080094a88.shtml
 How OSPF Injects a Default Route into a Normal
Area
– />ation_example09186a00801ec9f0.shtml
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