Limiting null route time by detecting Packet Forwarding Engine destinations that are unreachable over the fabric

Enables to limit null route time by detecting unreachable destination Packet Forwarding Engines. The router signals neighboring routers when it cannot carry traffic because of the inability of some or all source Packet Forwarding Engines to forward traffic to some or all destination Packet Forwarding Engines on any fabric plane, after interfaces have been created. This inability to forward traffic results in a traffic null route by the system. When the system detects unreachable Packet Forwarding Engine destinations, it attempts to heal the traffic null route. If the healing fails, the system turns off the interfaces, thereby stopping the traffic null route and initiating the recovery process. The recovery process consists of the following steps:

• Fabric plane restart phase: Healing is attempted by restarting the fabric planes one by one.
• Fabric plane and FPC restart phase: Healing is attempted by restarting both the fabric planes and the FPCs. If there are bad FPCs that are unable to initiate high-speed links to the fabric after reboot, traffic null routes are limited because no interfaces are created for these FPCs.
• FPC offline phase: Traffic null routes are limited by turning the SIBs offline and by turning off interfaces because previous attempts at recovery have failed.