fabric-load-balance

Implement ALB by using flowlets.

When ALB is implemented using flowlets, traffic flows that enter the VCF are spliced into smaller flows—flowlets—and individually forwarded across the VCF to the same destination device over different paths when the inactivity time between packet bursts on the sending interface exceeds the user-configurable inactivity interval.

The inactivity interval is 16 microseconds by default, and can be configured using the inactivity-interval statement. You should configure the inactivity interval to ensure in-order packet delivery, so that overall performance is not negatively impacted by the packet reordering process at the receiving device. To ensure in-order packet delivery, the inactivity interval should be larger than the largest latency skew among all the paths in the VCF from any node to any other node.

Implementing ALB using flowlets is especially effective in environments that periodically experience extremely large traffic flows—elephant flows—that are substantially larger than the majority of other traffic flowing through the VCF. The VCF is better able to manage elephant flows by splicing them into smaller flowlets using ALB.

Implement ALB using per-packet mode.

When per-packet mode is enabled, the VCF forwarding algorithm dynamically monitors all paths in the VCF and forwards packets to destination devices using the best available path at that moment. Flows are reordered at the destination node when per-packet mode is used to enable ALB, so some performance impact due to packet reordering is experienced.