Configuring PFC on an Ethernet interface

PFC performs flow control based on 802.1p priorities. With PFC enabled, an interface requires its peer to suspend sending packets with certain 802.1p priorities when congestion occurs. By decreasing the transmission rate, PFC helps avoid packet loss.

If you enable PFC and configure the priority-flow-control no-drop dot1p dot1p-list command on both ends, the local port processes a received packet as follows when network congestion occurs:

If PFC is enabled for the 802.1p priority carried in the packet, the local port perform the following tasks:
- Accepts the packet.
- Notifies the peer to stop sending packets carrying the 802.1p priority until the congestion is removed.
If PFC is disabled for the 802.1p priority carried in the packet, the local port drops the packet.

To configure PFC on an Ethernet interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Ethernet interface view.	interface interface-type interface-number	N/A
3. Enable PFC on the interface through automatic negotiation or forcibly.	priority-flow-control { auto \| enable }	By default, PFC is disabled.
4. Enable PFC for 802.1p priorities.	priority-flow-control no-drop dot1p dot1p-list	By default, PFC is disabled for all 802.1p priorities.

When you configure PFC, follow these guidelines:

To perform PFC on a network port of an IRF member device, configure PFC on both the network port and the IRF physical ports. For information about IRF, see IRF configuration Guide.
As a best practice to ensure correct operations of IRF and other protocols, do not enable PFC for 802.1p priorities 0, 6, and 7.
Perform the same PFC configuration on all ports that traffic travels through.
A port can receive PFC pause frames regardless of whether PFC is enabled on the port. However, only a port with PFC enabled can process PFC pause frames. To make PFC take effect, make sure PFC is enabled on both the local end and the peer end.

The relationship between the PFC feature and the generic flow control feature is shown in Table 1.

Table 1: The relationship between the PFC feature and the generic flow control feature

flow-control	priority-flow-control enable	priority-flow-control no-drop dot1p	Remarks
Unconfigurable	Configured	Configured	You cannot enable flow control by using the flow-control command on a port where PFC is enabled and PFC is enabled for the specified 802.1p priority values.
Configured	Configurable	Unconfigurable	On a port configured with the flow-control command, you can enable PFC, but you cannot enable PFC for specific 802.1p priorities. Enabling both generic flow control and PFC on a port disables the port from sending common or PFC pause frames to inform the peer of congestion conditions. However, the port can still handle common and PFC pause frames from the peer.

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