Learn how to enable nonstop forwarding with stateful switchover (NSF/SSO).

Recipe:
Config SSO first
Router> enable
Router# configure terminal
Router(config)# redundancy
Router(config-red)# mode sso
Router(config-red)# end

Router# show redundancy states

Multicast MLS on by default

enable in routing process
router(config)#router ospf 120
router(config-router)nsf

Additional Technical Information
Cisco Catalyst 4500 E-Series High Availability - White Paper