In group mode, two or more appliances become a single virtual appliance. This mode is one solution to the problem of asymmetric routing, which is defined as any case in which some packets in a given connection pass through a given appliance but others do not. A limitation of the appliance architecture is that acceleration cannot take place unless all packets in a given connection pass through the same two appliances. Group mode overcomes this limitation.
Group mode can be used with multiple or redundant links without reconfiguring your routers.
Group mode applies only to the appliances on one side of the WAN link; the local appliances neither know nor care whether the remote appliances are using group mode.
Group mode uses a heartbeat mechanism to verify that other members of the group are active. Packets are forwarded to active group members only.
Avoiding asymmetric routing is the main reason to use group mode, but group mode is not the only method available for that purpose. If you decide that it is the best method for your environment, you can enable it by setting a few parameters. If the default mechanism for determining which appliance is responsible for a particular connection does not provide optimal acceleration, you can change the forwarding rules.