How Does Stateful Synchronization Work?

Stateful Synchronization is not load-balancing. It is an active-standby configuration where the Primary Security Appliance handles all traffic. When Stateful Synchronization is enabled, the Primary Security Appliance actively communicates with the Secondary to update most network connection information. As the Primary Security Appliance creates and updates network connection information (such as VPN tunnels, active users, connection cache entries), it immediately informs the Secondary Security Appliance. This ensures that the Secondary Security Appliance is always ready to transition to the Active state without dropping any connections.

The synchronization traffic is throttled to ensure that it does not interfere with regular network traffic. All configuration changes are performed on the Active Security Appliance and automatically propagated to the Standby Security Appliance. The High Availability pair uses the same LAN and WAN IP addresses—regardless of which Security Appliance is currently Active.

When using SonicWall Network Security Manager (NSM) to manage the Security Appliances, NSM logs into the shared WAN IP address. In case of a failover, NSM administration continues seamlessly, and NSM administrators currently logged into the Security Appliance are not logged out; however, Get and Post commands may result in a time out with no reply returned.

Synchronized and non-synchronized information table lists the information that is synchronized and information that is not currently synchronized by Stateful Synchronization.

Synchronized and non-synchronized information

Information that is Synchronized	Information that is not Synchronized
VPN information	Dynamic WAN clients (L2TP, PPPoE, and PPTP)
Basic connection cache	Deep Packet Inspection (GAV, IPS, and Anti Spyware)
FTP	IPHelper bindings (such as NetBIOS and DHCP)
Oracle SQL*NET	SYNFlood protection information
Real Audio	Content Filtering Service information
RTSP	VoIP protocols
GVC information	Dynamic ARP entries and ARP cache time outs
Dynamic Address Objects	Active wireless client information
DHCP server information	Wireless client packet statistics
Multicast and IGMP	Rogue AP list
Active users
ARP
SonicPoint and SonicWave status
Wireless guest status
Weighted Load Balancing information
Dynamic Routing Configuration The configuration is synchronized, but the routing table has to be rebuilt in a failover.