• 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
  • Understanding High Availability
  • Understanding SonicWall High Availability Operation Modes
  • 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
    • Connecting the Active/Active DPI Interfaces for Active/Active DPI
  • 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
  • Configuration of HA Active/Standby
  • Configuring Active/Standby High Availability Settings
  • Configuring HA with Dynamic WAN Interfaces
  • Configuring Network DHCP and Interface Settings
    • Disabling the SonicOS DHCP Server
    • Configuring Virtual IP Addresses
    • Configuring Redundant Ports
• 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
• Failure Monitoring
• SonicWall Support
  • About This Document

Failure Monitoring

When setting up HA, you must configure a monitoring method to detect an HA event. You may configure either physical or logical monitoring.

MANAGE | System Setup > High Availability > Monitoring Settings

Physical interface monitoring means enabling link detection for the designated HA interfaces. The link is sensed at the physical layer to determine link viability. This means that if a cable is connected and has power and HA event may not occur even if the layer 3 functionality becomes lost. Physical interface monitoring is best used when the appliance is operating in transparent mode.

Logical monitoring involves configuring the SonicWall to monitor a reliable layer 3 device on one or more of the connected networks.

Failure to periodically communicate with the device by the Active unit in the HA Pair triggers a failover to the Standby unit.

If neither unit in the HA Pair can connect to the device, no action is taken.

Active/Active Failover

There are two types of failover that can occur when Active/Active Clustering is enabled

• High Availability failover - Within an HA pair, the Secondary unit takes over for the Primary. If Stateful HA is enabled for the pair, the failover occurs without interruption to network connections.

No lost connections if within a stateful HA pair

• Active/Active failover - If all the units in the owner node for a Virtual Group encounter a fault condition, then the standby node for the Virtual Group takes over the Virtual Group ownership. Active/Active failover transfers ownership of a Virtual Group from one Cluster Node to another. The Cluster Node that becomes the Virtual Group owner also becomes the owner of all the virtual IP addresses associated with the Virtual Group and starts using the corresponding virtual MAC addresses.

  

  Outside a stateful HA pair, connections will be reset

  Active/Active failover is stateless, meaning that network connections are reset, and VPN tunnels must be renegotiated. Layer 2 broadcasts inform the network devices of the change in topology as the Cluster Node which is the new owner of a Virtual Group generates ARP requests with the virtual MACs for the newly owned virtual IP addresses. This greatly simplifies the failover process as only the connected switches need to update their learning tables. All other network devices continue to use the same virtual MAC addresses and do not need to update their ARP tables, because the mapping between the virtual IP addresses and virtual MAC addresses is not broken. When both High Availability failover and Active/Active failover are possible, HA failover is given precedence over Active/Active failover for the following reasons:

  • HA failover can be stateful, whereas Active/Active failover is stateless.
  • The standby firewall in an HA pair is lightly loaded and has resources available for taking over the necessary processing, although it may already be handling DPI traffic if Active/Active DPI is enabled. The alternative Cluster Node might already be processing traffic comparable in amount to the failed unit, and could become overloaded after failover

  Active/Active failover always operates in Active/Active preempt mode. Preempt mode means that, after failover between two Cluster Nodes, the original owner node for the Virtual Group will seize the active role from the standby node after the owner node has been restored to a verified operational state. The original owner has a higher priority for a Virtual Group due to its higher ranking if all virtual IP interfaces are up and the link weight is the same between the two Cluster Nodes.