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SonicOS 5.8.1 Administrator Guide
Stateful High Availability Example
The following figure shows a sample Stateful High Availability network.
In case of a failover, the following sequence of events occurs:
1. A PC user connects to the network, and the Primary SonicWALL security appliance creates
a session for the user.
2. The Primary appliance synchronizes with the Backup appliance. The Backup now has all
of the user’s session information.
3. The power is unplugged from the Primary appliance and it goes down.
4. The Backup unit does not receive heartbeat messages from the Primary appliance and
switches from Idle to Active mode.
5. The Backup appliance begins to send gratuitous ARP messages to the LAN and WAN
switches using the same Virtual MAC address and IP address as the Primary appliance. No
routing updates are necessary for downstream or upstream network devices.
6. When the PC user attempts to access a Web page, the Backup appliance has all of the
user’s session information and is able to continue the user’s session without interruption.
SonicWALL NSA 1
SonicWALL NSA 2
B
Network Security Appliance
NSA
Local Network
SonicWALL
HA / Failover Pair
Internet
HA Link