This document describes how the OSPF behavior varies before and after the OSPF local RIB implementation.
In OSPF, distribute list can be used to exclude specific LSA from SPF calculation. However, this behavior was also changed after the OSPF local RIB implementation.
Before implementation change: When the best path LSA is excluded, the next valid path is calculated
After implementation change: When the best path LSA is excluded, the next valid path is not calculated
This change was made because routing loops may occur when calculation results are different between a router that uses distribute-list and another that does not.
Due to this change, expected path calculation may not be performed when the IOS version of a device that uses distribute-list in OSPF is changed.For more details on versions that support OSPF local RIB, refer to Feature Navigator.
Details on the changes before and after the implementation are explained below, based on the following configuration.