13.3.3 Behavior in case of link failure

(1) Example of Operation at Link Failure

The following figure shows an operation example when a link fails.

Figure 13-7: Example of operation when a link failure occurs

In this figure, Switch A is the master switch and Switch B is the backup switch. Failures have occurred on the link between Switches A and C, on the link between Switches A and D, and on the link between Switches B and E. For Switches A and B, the number of active ports is the top-priority condition in the master/backup selection conditions. Because Switch B has more active ports than Switch A, Switch B becomes the master Switch. Before Switch B enters the master state, it enters the backup (wait for master) state. In the backup (wait for master) state, Switch B waits for a GSRP Advertise frame from Switch A. When Switch B receives a GSRP Advertise frame, it makes sure that Switch A is in the backup state and then enters the master state. Note that the example in this figure shows that Switch E cannot establish communication because the link between Switch E and Switch B (master switch) has failed.

(2) Function to prevent continuous switching when link is unstable

GSRP uses the number of active ports as the top-priority condition for selecting the master and backup switches. If links become unstable (for example, links frequently come up and go down), the number of active ports also changes frequently, resulting in repeated switchover between the master and backup switches.

For this purpose, GSRP provides the port-up-delay configuration command that you can use to specify a delay time during which link ports that are up are not counted as active ports. This specification prevents unnecessary switchovers when links are unstable.

In the port-up-delay command, you can specify a value in one-second units in the range from 1 to 43200 seconds (12 hours). If you specify infinity, the delay time is unlimited. If you are sure the links are stable, you can use the clear gsrp port-up-delay operation command to start counting the number of active ports without waiting for the delay time you specified in the port-up-delay command to expire.