Core Issue
The Open Shortest Path First (OSPF) Nonstop Forwarding (NSF) Awareness feature is used to minimize the amount of time a network is unavailable following a switchover. The NSF feature is enabled by default and adds extra bytes to the end of OSPF packets, making the packet size larger. Devices that do not support this feature should ignore these extra bytes. However, certain devices might not be able to do so, causing the hello packets to be dropped. This prevents OSPF routers from becoming neighbors.
Resolution
To disable NSF awareness, disable the use of the Link-Local Signalling (LLS) data block in originated OSPF packets by issuing the no capability lls command in router configuration mode.
For more information, refer to OSPF Nonstop Forwarding (NSF) Awareness.
For more information on NSF, refer to the Configuring OSPF NSF section of Cisco Nonstop Forwarding.
