13.1.2 Key Features

(1) Avoiding Simultaneous Master State

When GSRP is enabled, the paired Switches send and receive control frames on the direct link between them to check each other's status. When a link failure is detected, if control frames are successfully sent and received, the switches automatically switch over. The master Switch makes sure that the neighbor Switch is operating in the backup state, and then the backup Switch takes over as the master Switch. This precaution prevents the two Switches from being in the master state at the same time.

If the master Switch fails, control frames cannot be successfully sent and received, and neither Switch is able to check the status of the neighbor Switch. Accordingly, the Switches need to be manually switched over. The reason is that the failed master Switch might still be operating in the master state. If the backup Switch automatically enters the master state, the two Switches would be in the master state. Manual switchover is necessary to avoid this problem. The assumption is that the user takes action for the failure and determines that it is safe to allow the backup switch to enter the master state before manually changing the backup switch to the master state. Besides manual switchover, GSRP also supports automatic switchover. When a Switch detects a failure on the direct link with the neighbor Switch, the switch assumes that a failure has occurred on the neighbor Switch and automatically takes over.

(2) Limiting the Transmission Range of Control Frames

To avoid sending control frames to unnecessary locations, GSRP limits the range for sending and receiving control frames only to the specified VLANs.