configuring and verifying ospf route summarization
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Implementing a Scalable Multiarea Network OSPF-Based Solution

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Configuring and Verifying OSPF Route Summarization. Implementing a Scalable Multiarea Network OSPF-Based Solution. Summarization. Networks are normally translated into type 3 LSAs in other areas. Route summarization is the consolidation of advertised addresses.

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Presentation Transcript
summarization
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.
benefits of route summarization
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
interarea route summarization
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.
using route summarization
Using Route Summarization
  • Interarea summary link carries a mask
  • One or more entries can represent several subnets
configure interarea route summarization
Configure Interarea Route Summarization
  • Configures type 3 summarization on ABRs
external route summarization
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
configure external route summarization
Configure External Route Summarization
  • Configures type 5 summarization of redistributed routes on ASBRs
default routes in ospf
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
configure ospf default route
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).
summary
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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