13.3.2 Operation in case of device failure

The following figure shows an example of how a GSRP switch operates when it fails.

Figure 13-5: Operation in the event of a switch failure

When the master Switch (Switch A) is unable to successfully send GSRP Advertise frames due to a failure on the switch, switch B detects a timeout for receiving GSRP Advertise frames from switch A. At this point, Switch B enters the backup (neighbor unknown) state. In this state, as in the backup state, Switch B does not relay frames. When a switch is in the backup (neighbor unknown) state, it outputs a message prompting the user to check its state.

GSRP supports two methods for changing the state of Switch B from backup (neighbor unknown) to master: manual switchover and automatic switchover.

<Structure of this section>

(1) Switching manually (by operation command)

GSRP supports the set gsrp master operation command to manually change the switch state to the master state. Before the user executes this command to change the state of Switch B to the master state, the user must check whether the ports on Switch A are blocked or whether Switch A is deactivated. The following figure shows what happens after the set gsrp master operation command is entered.

Figure 13-6: Operation after an operation-command set gsrp master is entered

(2) Automatic switching (switching by direct link failure detection)

For automatic switchover, GSRP supports functionality that detects a direct-link failure. GSRP also supports functionality for switchover to the master state by independently started GSRP switches. This is not handled by the direct-link failure detection functionality.

Direct-link failure detection functionality

To enable the detection of direct-link failures, specify the direct-down parameter in the no-neighbor-to-master configuration command.

This functionality can be used after a switch has been started and has received a GSRP Advertise frame from the neighbor switch. When a switch discovers that the direct-link port is down after it enters the backup (neighbor unknown) state, the backup switch assumes that the neighbor switch has failed and automatically switches to the master state.

Because the status of the partner switch is unknown until GSRP Advertise frames from the partner switch are received from the switch startup *1, switching is not performed automatically by the direct link failure detection function. If you want to make the switch the master in this case, manually set the switch as the master. If you want to perform automatic switchover after a switch has been started but before it has received a GSRP Advertise frame from the neighbor switch, use the functionality for switchover to the master state by an independently started GSRP switch.
Functionality for switchover to the master state by an independently started GSRP switch

To enable switchover to the master state by an independently started GSRP switch, specify the direct-down forced-shift-time parameter in the no-neighbor-to-master configuration command.

This function operates only when GSRP switching on the other side does not start due to a fault and the direct link is not up from the switch startup*2.

When all the conditions*3 for starting the master transition function when GSRP switch is started independently are satisfied, the system enters the automatic master transition wait state. After the automatic master transition wait time set in the parameter forced-shift-time has elapsed, the system automatically transitions to the master state.

When a switch is in the automatic master wait state, you can use the clear gsrp forced-shift operation command to cancel the state to prevent the switch from automatically entering the master state.

This functionality places the switch in the master state without knowing the state of the neighbor switch. Set the time until the switch automatically operates as a master to ensure that the port on the partner switch is blocked or that the switch is not running.

Note #1

A switch is assumed to have been started when any of the following operations is performed:

Executing the restart vlan operation command
Executing the restart gsrp operation command
Specifying direct-down for no-neighbor-to-master in the gsrp configuration command.
Configuring a direct-link port by using direct-link in the grsp configuration command.
Applying the setting to the running configuration by using the copy operation command

Note #2

The switchover to the master state by an independently started GSRP switch is performed in the same way as when a switch has been started by any of the following operations:

Executing the restart vlan operation command
Executing the restart gsrp operation command
Applying the setting to the running configuration by using the copy operation command

Note #3

The conditions for starting the switchover to the master state by an independently started GSRP switch as follows:

The timeout period for receiving GSRP Advertise frames expires.
Any of the member ports in the VLAN groups configured for a Switch is enabled.