Dell PowerConnect B-FCXs, Configuration Manual

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360 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Virtual Switch Redundancy Protocol (VSRP)
10
•
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
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.
VSRP
M as ter
VSRP
B a ck u p
option a l link
VSRP
Aw a re
VSRP
Aw a re
VSRP
Aw a re
F F F
B
B
B
Config u red priority = 100
Act ua l priority = 100 * (3/3) = 100
Config u red priority = 100
Act ua l priority = 100 * (3/3) = 100