Priority-based Flow Control
Priority flow control (PFC) is defined in the IEEE 802.1Qbb standard as an extension of the IEEE 802.3x flow control standard. When buffer congestion is detected, IEEE 802.3x flow control allows the communicating device to pause all traffic on the port, whereas PFC allows the device to pause just a portion of the traffic and allow other traffic on the same port to continue.
The rest of this section provides general guidelines for configuring the ExtremeXOS PFC feature for DCB operation. After you configure PFC, DCBX advertises the PFC compatible configuration to DCBX peers on all DCBX enabled ports.
enable flow-control rx-pause qosprofile qp5 ports 1-24
The tx-pause option is configured on the priority itself. For example, the following command enables the transmittal of PFC Pause frames for priority 4 when frames with priority 4 are congested:
enable flow-control tx-pause priority 4 ports 1-24
The tx-pause configuration determines what is advertised in the DCBX PFC TLV. In order for PFC to work correctly, it is important to ensure that all switches in the DCB network are receiving and transmitting PFC consistently for each priority on all ports.
In summary, the following three commands ensure that PFC is enabled for priority 4 traffic on ports 1-24:
configure dot1p type 4 qosprofile qp5 enable flow-control rx-pause qosprofile qp5 ports 1-24 enable flow-control tx-pause priority 4 ports 1-24