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High Availability
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SonicOS 5.8.1 Administrator Guide
Note SonicWALL High Availability cannot be configured using the built-in wireless interface, nor
can it be configured using Dynamic WAN interfaces.
The selected interface must be the same one that you physically connected as described in
“Initial Active/Active DPI Setup” on page 1144.
Step 7 To configure the High Availability Pair so that the Primary unit takes back the Primary role once
it restarts after a failure, select Enable Preempt Mode. Preempt mode is recommended to be
disabled when enabling Stateful High Availability, because preempt mode can be over-
aggressive about failing over to the Backup appliance.
Step 8 To back up the settings when you upgrade the firmware version, select Generate/Overwrite
Backup Firmware and Settings When Upgrading Firmware.
Step 9 Select the Enable Virtual MAC checkbox. Virtual MAC allows the Primary and Backup
appliances to share a single MAC address. This greatly simplifies the process of updating
network ARP tables and caches when a failover occurs. Only the switch to which the two
appliances are connected needs to be notified. All outside devices will continue to route to the
single shared MAC address.
Step 10 Optionally adjust the Heartbeat Interval to control how often the two units communicate. The
default is 5000 milliseconds; the minimum supported value is 1000 milliseconds. You can use
higher values if your SonicWALL handles a lot of network traffic.
Step 11 Set the Failover Trigger Level to the number of heartbeats that can be missed before failing
over. The default is 5.
Step 12 Set the Probe Interval to the interval in seconds between probes sent to specified IP
addresses to monitor that the network critical path is still reachable. This is used in logical
monitoring. SonicWALL recommends that you set the interval for at least 5 seconds. The
default is 20 seconds, and the allowed range is 5 to 255 seconds. You can set the Probe IP
Address(es) on the High Availability > Monitoring screen. See “High Availability > Monitoring”
on page 1161.
Step 13 Set the Probe Count to the number of consecutive probes before SonicOS Enhanced
concludes that the network critical path is unavailable or the probe target is unreachable. This
is used in logical monitoring. The default is 3, and the allowed range is 3 to 10.
Step 14 Set the Election Delay Time to the number of seconds allowed for internal processing between
the two units in the High Availability Pair before one of them takes the Primary role. The default
is 3 seconds.
Step 15 Set the Dynamic Route Hold-Down Time to the number of seconds the newly-Active
appliance keeps the dynamic routes it had previously learned in its route table. This setting is
used when a failover occurs on a High Availability pair that is using either RIP or OSPF dynamic
routing. When a failover occurs, Dynamic Route Hold-Down Time is the number of seconds