Implementing a Scalable Multiarea Network OSPF-Based Solution
© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-1 Implementing a Scalable Multiarea...
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Transcript of © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-1 Implementing a Scalable Multiarea...
![Page 1: © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-1 Implementing a Scalable Multiarea Network OSPF- Based Solution Configuring and Verifying.](https://reader035.fdocuments.net/reader035/viewer/2022062600/5a4d1bc77f8b9ab0599d5890/html5/thumbnails/1.jpg)
© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-1
Implementing a Scalable Multiarea Network OSPF-Based Solution
Configuring and Verifying OSPF Route Summarization
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-2
Summarization Networks are normally translated into type 3 LSAs in other areas. Route summarization is the consolidation of advertised
addresses. – On ABR, summarize type 3 LSAs– On ASBR, summarize type 5 LSAs
A good addressing plan is required. A drawback is the possibility of suboptimal routing.
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-3
Benefits of Route Summarization Minimizes the number of routing table entries Localizes the impact of a topology change Reduces LSA flooding and saves CPU resources
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-4
Interarea Route Summarization A summary route will be generated if at least one subnet within
the area falls in the summary address range. A summarized route metric will be equal to the lowest cost of all
subnets within the summary address range. Only for the summary routes of connected areas:
– The ABR creates a route to Null 0 to avoid loops.
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-5
Using Route Summarization Interarea summary link carries a mask One or more entries can represent several subnets
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-6
Configure Interarea Route Summarization Configures type 3 summarization on ABRs
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-7
Route Summarization Configuration Example at the ABR
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-8
External Route Summarization Summarization can be used for external routes:
– on an AS boundary for type 5 LSAs (redistributed routes)– on an NSSA ABR for type 5 translated from type 7
A summary route to Null 0 will be created for each summary range
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-9
Configure External Route Summarization Configures type 5 summarization of redistributed routes on
ASBRs
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-10
Route Summarization Configuration Example at ASBR
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-11
Default Routes in OSPF A default route is injected into OSPF as an external type 5 LSA. Default route distribution is not on by default. Benefits of default routes include:
– A smaller routing table– Fewer resources used in the router
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-12
Configure OSPF Default Route The first command allows the ASBR to originate a type 5 default
route if it has the gateway of last resort. The second command allows the ASBR to originate a type 5
default route even if there is no gateway of last resort (optional). Use the route map to define a dependency on any condition
inside the route map (optional).
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-13
Default Route Configuration Example
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-14
Summary Route summarization improves CPU utilization, reduces LSA
flooding, and reduces routing table sizes. The area range command is used to summarize at
the ABR. The summary-address command is used to summarize at the ASBR.
Default routes can be used in OSPF to prevent the need for a specific route to each destination network. The benefits include a much smaller routing table and an LSDB with complete reachability.
OSPF uses the default-information originate command to inject a default route.
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© 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—3-15