Enabling and Disabling CoS Symmetric Ethernet PAUSE Flow Control

Ethernet PAUSE flow control is a congestion relief feature that works by providing link-level flow control for all traffic on a full-duplex Ethernet link, including Ethernet links that belong to Ethernet link aggregated (LAG) interfaces. Ethernet PAUSE works in both directions on the link. In one direction, an interface generates and sends PAUSE messages to stop the connected peer from sending more traffic. In the other direction, the interface responds to PAUSE messages it receives from the connected peer to stop sending traffic.

Symmetric flow control means that an interface has the same PAUSE configuration in both directions. The PAUSE generation and PAUSE response functions are both configured as enabled, or they are both disabled.

Asymmetric flow control allows you to configure the PAUSE functionality in each direction independently on an interface. The configuration for generating PAUSE messages and for responding to PAUSE messages does not have to be the same. It can be enabled in both directions, disabled in both directions, or enabled in one direction and disabled in the other direction. If you do not want to PAUSE all of the traffic on a link, you can use priority-based flow control (PFC) to selectively pause traffic based on its IEEE 802.1p code point.

On any particular interface, symmetric and asymmetric flow control are mutually exclusive. If you attempt to configure both features, the switch returns a commit error. Ethernet PAUSE and PFC are also mutually exclusive features, so you cannot configure both of them on the same interface. If you attempt to configure both Ethernet PAUSE and PFC on an interface, the switch returns a commit error.