Understanding Fast-Path Processing

All packets undergo fast path-processing. However, if a session exists for a packet, the packet undergoes fast-path processing and bypasses the first-packet process. When there is already a session for the packet’s flow, the packet does not transit the central point.

Here is how fast-path processing works: NPUs at the egress and ingress interfaces contain session tables that include the identification of the SPU that manages a packet’s flow. Because the NPUs have this session information, all traffic for the flow, including reverse traffic, is sent directly to that SPU for processing.

To illustrate the fast-path process, this section uses an example with a source “a” and a destination “b”. The direction from source to destination for the packets of the flow is referred to as (a->b). The direction from destination to source is referred to as (b->a).

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