Looking for various documents and the IEEE standards, I can see that 802.3bd-2011 adds a MAC control frame for priority-based flow control. How does priority-based flow control differ from IEEE 802.1P/802.1D-2004 (which is now in IEEE 802.1Q-2005).

In IEEE 802.1Q we have PCP values for QoS at layer 2;

  1. Is priority based flow control something different then, to PCP values?

  2. According to Wikipedia, 802.3bd was:

An amendment by the IEEE 802.1 Data Center Bridging Task Group (802.1Qbb) to develop an amendment to IEEE Std 802.3 to add a MAC Control Frame to support IEEE 802.1Qbb Priority based Flow Control.

What was the need for this?

Please provide a/some references for your answer so I can read them.

  • 2
    Data Center Bridging = IEEE standardization of FCoE functionality... I use standardization in the loosest possible way, FCoE is a nightmare of individual vendor interpretations Jun 5, 2013 at 19:42

1 Answer 1


This is used to support FCoE as FC cannot handle dropped packets.


  • I see, so Ethernet has been extended to support FCoE. I haven't found the time to get my dirty little mitts on FCoE in the lab yet so I have a knowledge gap here: I thought FCoE didn't run over "regular Ethernet"? To clarify, you can't run FCoE over any old Ethernet switch for example, you need a Nexus 5k (using Cisco as an example). So where does this extension of Ethernet fit in? Is it that FCoE hosts, their HBA's and FCoE switches support this extensions, but typical Ethernet hosts and switches don't?
    – Baldrick
    Jun 5, 2013 at 19:45
  • I wouldn't go so far as to say you can't run FCoE over regular switches but rather that it is HIGHLY discouraged due to the lossless nature of FC. Jun 5, 2013 at 21:22

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