Configuring Priority Flow Control

With PFC, it is expected that both RX and TX be enabled or disabled.

To enable PFC, use the following command:
enable flow-control [tx-pause {priority priority} | rx-pause {qosprofile qosprofile}] ports [all | port_list]

To disable PFC, use the following command:

disable flow-control [tx-pause {priority priority} | rx-pause {qosprofile qosprofile}] ports [all | port_list]

Example

The network needs to transport FCoE (Fiber Channel over Ethernet) traffic which is intermixed with other more typical LAN traffic on the same Ethernet network. FCoE needs a lossless transport and PFC can be used to enable this. You define QoS profiles for all eight traffic priorities. At the network level, it is decided that FCoE traffic will be assigned to priority 3 (which corresponds to QP4) and the remaining traffic is assigned to one or more other priorities. For this example, it is also assumed that the priority bits in the incoming packets are also 3.

One mechanism that can be used for this classification is the use of Access Control Lists (ACLs) that match on the FCoE ethertypes (0x8906 and 0x8914) using the ethernet-type qualifier with an action of QoS profile QP4 for both rules. Other traffic can be classified to other priorities. Once this configuration is applied, FCoE is now separated from the other Ethernet traffic and is assigned a priority of 3 through the switch.

PFC is enabled at the ports that will see FCoE traffic, in this case, ports 1:1, 2:3, and 6:5.

Since FCoE is assigned to QP4, you would enable the receive PFC for QoS profile to be QP4 and, in this example, would also enable PFC with a transmit priority of 3. The enable commands would then read as follows:

enable flow-control tx-pause priority 3 ports 1:1,2:3,6:5
enable flow-control rx-pause qosprofile qp4 ports 1:1,2:3,6:5

The show port flow-control rx-pause no-refresh command displays the following information. With the no-refresh option the display shows the following information:

# show ports 1,5,9 flow-control rx-pauses no-refresh 
Flow Control Frames Received
Port   Pause   PFC0   PFC1   PFC2   PFC3   PFC4   PFC5   PFC6   PFC7
        Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs
==============================================================================
1          -      -      -      - 1234567 1234567    - 1234567     -
5          -      -      -      - 1234567 1234567    - 1234567     -
16:104 1234567    -      -      -       -       -    -       -     -
===============================================================================
">" Name truncated, "-" rx-pause not enabled, "." Counter not available

Without the no-refresh option the display refreshes until interrupted by the console operator pressing Escape:

# show ports 1,5,9 flow-control rx-pauses
Flow Control Frame Monitor                     Sat Aug 18 19:35:12 2012
Port   Pause   PFC0   PFC1   PFC2   PFC3   PFC4   PFC5   PFC6   PFC7
        Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs   Rcvs
==============================================================================
1          -      -      -      - 1234567 1234567    - 1234567     -
5          -      -      -      - 1234567 1234567    - 1234567     -
16:104 1234567    -      -      -       -       -    -       -     -
===============================================================================
">" Name truncated, "-" rx-pause not enabled, "." Counter not available
Spacebar->Toggle screen 0->Clear counters U->Pageup D->Pagedown ESC->exit

The new show port flow-control tx-pause no-refresh CLI command displays the following information. With the no-refresh option the display shows the following information:

# show ports 1,5,9 flow-control tx-pauses no-refresh 
Flow Control Frames Transmitted
Port   Pause   PFC0   PFC1   PFC2   PFC3   PFC4   PFC5   PFC6   PFC7
       Xmts    Xmts   Xmts   Xmts   Xmts   Xmts   Xmts   Xmts   Xmts
==============================================================================
1         -       -      -      - 1234567 1234567    - 1234567    -
5         -       -      -      - 1234567 1234567    - 1234567    -
16:104 1234567    -      -      -       -       -    -       -    -
===============================================================================
">" Name truncated, "-" tx-pause not enabled, "." Counter not available

Without the no-refresh option the display refreshes until interrupted by the console operator pressing the escape key:

# show ports 1,5,9 flow-control tx-pauses
Flow Control Frame Monitor Sat Aug 18 19:35:12 2012
Port   Pause   PFC0   PFC1   PFC2   PFC3   PFC4   PFC5   PFC6   PFC7
        Xmts   Xmts   Xmts   Xmts   Xmts   Xmts   Xmts   Xmts   Xmts
==============================================================================
1          -      -      -      -  1234567 1234567   -  1234567    -
5          -      -      -      -  1234567 1234567   -  1234567    -
16:104 1234567    -      -      -        -       -   -        -    -
===============================================================================
">" Name truncated, "-" tx-pause not enabled, "." Counter not available
Spacebar->Toggle screen 0->Clear counters U->Pageup D->Pagedown ESC->exit

Once this configuration is complete, if a switch ingress port detects congestion, it will send PFC packets to the remote link partner and will respond to PFC packets from the remote link partner by stopping transmit.