Standby module operations
The standby management module with OSPF configuration performs the following functions:
Neighbor database
Neighbor information is updated in the standby module based on updates from the active module. Certain neighbor state and interface transitions are synchronized to the standby module. By default, the neighbor timers on the standby module are disabled.
LSA database
The standby module processes LSA synchronization events from the active module and unpacks the LSA synchronization information to directly install it in its LSDB, as the LSA has already been processed on the active module. The information required to install all types of LSAs (and special LSAs such as Grace LSAs) is packed by OSPF on the active module in the synchronization buffer, so that you can directly install LSAs on the standby module without extra processing.
The standby module is not allowed to originate any LSAs of its own. This is to maintain all information consistently from the active module. The active module synchronizes self-originated LSAs to the standby module.
LSA aging is not applicable on the standby module. During synchronization from the active module, the current LSA age is recorded and the new database timestamp is created on the standby module to later derive the LSA age as needed.
When the active module sends the LSAs to the standby module, based on the message, the standby module deletes or updates its LSDB with the latest information.
LSA acknowledging or flooding are not done on the standby module. When the LSA synchronization update arrives from the active module, it will be directly installed into the LSDB.