H3C Technologies H3C S5560 Series Switches - Manual (Page 22)

8
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.
• To ensure correct operations of IRF and other protocols, H3C recommends not enabling 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-flo
w-control
enable
priority-flow-contr
ol 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.