• SonicOS 8
• About SonicOS
  • Working with SonicOS
  • SonicOS Workflow
  • How to Use the SonicOS Administration Guides
  • Guide Conventions
• High Availability
  • About High Availability
    • High Availability Terminology
    • High Availability Modes
    • High Availability Encryption
    • Crash Detection
    • Virtual MAC Address
    • Dynamic WAN Interfaces with PPPoE HA
    • Stateful Synchronization with DHCP
    • Stateful Synchronization with DNS Proxy
    • About HA Monitoring
  • About Active/Standby HA
    • Benefits of Active/Standby HA
    • Working of Active/Standby HA
  • About Stateful Synchronization
    • Benefits of Stateful Synchronization
    • How Does Stateful Synchronization Work?
    • Example of Stateful Synchronization
  • Active/Standby Prerequisites
    • Supported Platforms and Licensing for HA
    • Physically Connecting Your Security Appliances
  • Maintenance
    • Removing an HA Association
    • Replacing a SonicWall Security Appliance
      • Replacing an HA Primary Unit
      • Replacing an HA Secondary Unit
• High Availability Status
  • Active/Standby High Availability Status
    • High Availability Status
    • High Availability Config
    • High Availability Licenses
• Configuring High Availability
  • Configuring Active/Standby High Availability Settings
  • Configuring HA with Dynamic WAN Interfaces
• Configuring High Availability in the Cloud Platform
  • Set up an Active/Standby High Availability Configuration Using Azure
    • Install the Custom Template
    • Enable Identity of Both Virtual Machines (HA1 and HA2)
    • Role Assignment
    • Check the Networking Tab
    • Configuring Active NSv Firewall Using the Associated Public IP
    • Configuring Standby NSv Firewall Using the Associated Public IP
    • Enable the L3 Mode
    • Configuring Active NSv Firewall Using the Floating Public IP
    • Configuring HA to Active/Standby with L3 HA link
    • Adding Additional Floating Public IP
• Fine Tuning High Availability
  • Advanced Settings
  • Configuring Advanced High Availability Settings
• Monitoring High Availability
  • Configuring Active/Standby High Availability Monitoring
  • IPv6 High Availability Monitoring
  • IPv6 HA Monitoring Considerations
• Azure Use Cases
  • Use Case 1: Manage Azure HA Firewall
  • Use Case 2: Forward LAN traffic to the External Network through the Gateway after HA Failover
  • Use Case 3: Configure DNAT on Azure HA Firewall
  • Use Case 4: Configure DNAT on Azure HA Firewall (Need to move multiple floating IPs support)
• SonicWall Support
  • About This Document

Crash Detection

The HA feature has a thorough self-diagnostic mechanism for both the Active and Standby Security Appliances. The failover to the standby unit occurs when critical services are affected, physical or logical link failure is detected on monitored interfaces, or when the Security Appliance loses power.

The self-checking mechanism is managed by software diagnostics, which check the complete system integrity of the Security Appliance. The diagnostics check internal system statuses, system process statuses, and network connectivity. There is a weighting mechanism on both sides to decide which side has better connectivity to avoid potential failover looping.

Critical internal system processes such as NAT, VPN, and DHCP (among others) are checked in real time. The failing service is isolated as early as possible, and the failover mechanism repairs it automatically.