12.5.2 Helper function

(1) Operating conditions of helper function

The switch can operate as a helper router as long as the following conditions are met:

• It is not already acting as a helper for another restarting router in the same domain. In a given domain, the Switch can only act as a helper for one router at a time. If only one router is restarting, the switch provides the helper functionality on every interface that connects to the restarting router.

• It is not waiting to receive an ACK for an OSPF update packet sent to the restarting router.

(2) Cases where the helper function fails

The switch continues to operate as a helper router until the restarting router re-establishes adjacency or a notification is received indicating that the restarting router has exited the graceful-restart process.

To avoid potential conflicts with the routes maintained by the restarting router, the switch stops its helper functionality and recalculates its OSPF routes if any of the following events occurs:

• A new LSA (excluding periodic updates) is learned from a neighbor and advertised to the restarting router.

• The OSPF interface goes down.

• The switch loses or establishes adjacency with a router other than the restarting router, thus generating an LSA update.

• More than one router is restarting in the same OSPF domain.

• You use the graceful-restart mode command to disable helper mode in the switch configuration.