NP6 processors can offload sessions received by interfaces that are part of a redundant interface. You can combine two or more physical interfaces into a redundant interface to provide link redundancy. Redundant interfaces ensure connectivity if one physical interface, or the equipment on that interface, fails. In a redundant interface, traffic travels only over one interface at a time. This differs from an aggregated interface where traffic travels over all interfaces for distribution of increased bandwidth.
All offloaded traffic types are supported by redundant interfaces, including IPsec VPN traffic. Just like with normal interfaces, traffic accepted by a redundant interface is offloaded by the NP6 processor connected to the interfaces in the redundant interface that receive the traffic to be offloaded. If all interfaces in a redundant interface are connected to the same NP6 processor, traffic received by that redundant interface is offloaded by that NP6 processor. The amount of traffic that can be offloaded is limited by the capacity of the NP6 processor.
If a FortiGate has two or more NP6 processors connected by an integrated switch fabric (ISF), you can create redundant interfaces that include physical interfaces connected to different NP6 processors. However, with a redundant interface, only one of the physical interfaces is processing traffic at any given time. So you cannot use redundant interfaces to increase performance in the same way as you can with aggregate interfaces.
The ability to add redundant interfaces connected to multiple NP6s is supported by the integrated switch fabric (ISF) that allows multiple NP6 processors to share session information. Most FortiGate units with multiple NP6 processors also have an ISF. However, FortiGate models such as the 1000D, 2000E, and 2500E do not have an ISF. If you attempt to add interfaces connected to different NP6 processors to a redundant interface the system displays an error message.