Dell PowerConnect FCS624S Configuration Guide - Page 402

10 Virtual Switch Redundancy Protocol (VSRP) • If the Backup does not receive a Hello message with a higher priority than its own by the time the hold-down timer expires, the Backup becomes the new Master and starts forwarding Layer 2 traffic on all ports. If you increase the timer scale value, each timer value is divided by the scale value. To achieve sub-second failover times, you can change the scale to a value up to 10. This shortens all the VSRP timers to 10 percent of their configured values. VSRP priority calculation Each VSRP device has a VSRP priority for each VRID and its VLAN. The VRID is used during Master election for the VRID. By default, a device VSRP priority is the value configured on the device (which is 100 by default). However, to ensure that a Backup with a high number of up ports for a given VRID is elected, the device reduces the priority if a port in the VRID VLAN goes down. For example, if two Backups each have a configured priority of 100, and have three ports in VRID 1 in VLAN 10, each Backup begins with an equal priority, 100. This is shown in Figure 69 FIGURE 69 VSRP priority Configured priority = 100 Actual priority = 100 * (3/3) = 100 Configured priority = 100 Actual priority = 100 * (3/3) = 100 VSRP Master optional link VSRP Backup FF F BBB VSRP Aware VSRP Aware VSRP Aware However, if one of the VRID ports goes down on one of the Backups, that Backup priority is reduced. If the Master priority is reduced enough to make the priority lower than a Backup priority, the VRID fails over to the Backup. Figure 70 shows an example. 360 PowerConnect B-Series FCX Configuration Guide 53-1002266-01