Restrictions for OSPF Nonstop Routing
OSPF nonstop routing can significantly increase the memory used by OSPF during certain phases of its operation. CPU usage also can be increased. You should be aware of router memory capacity and estimate the likely memory requirements of OSPF nonstop Routing.
For more information, see Configuring OSPF Nonstop Routing. For devices where memory and CPU are constrained, you might want to consider using OSPF Nonstop Forwarding (NSF) instead. For more information, see OSPF RFC 3623 Graceful Restart Helper Mode.
A changeover from the active to the standby Route Processor (RP) can take several seconds, depending on the hardware platform, and during this time OSPF is unable to send Hello packets. As a result, configurations that use small OSPF dead intervals might not be able to maintain adjacencies across a changeover.