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Miscellaneous Notes

In addition to the OSPF configuration covered so far, extra basic features can also be implemented to tune the OSPF protocol and the communication between the OSPF-enabled routers, namely, route summarization and passive interfaces.

Route Summarization 

By default, no route summarization is performed on the routers when OSPF is enabled. For that reason, several problems can easily arise, such as: 

  • Large routing tables
  • Congestion
  • Low efficiency
  • Frequent LSA flooding throughout the areas in the AS

All these issues can be fixed by configuring summarization. It is an important technique that can help to improve the performance, stability, and scalability of OSPF networks and make the routing tables of the routers smaller, resulting in less resource consumption.

Passive Interfaces

Another very useful feature is using passive interfaces. When you enable OSPF, sometimes the protocol runs on interfaces that should not be involved in the OSPF communications, such as loopback interfaces or physical interfaces connecting to devices that are not OSPF-enabled. 

In such cases, unnecessary bandwidth and resources are spent sending hello packets every 10 seconds. Configuring passive interfaces provides several benefits, such as:

  • Prevents unnecessary OSPF adjacencies
  • Reduces useless OSPF traffic
  • Increases network security
  • Simplifies network administration