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Configuring DSCP-based PFC for Layer 3 Untagged Traffic

You can configure DSCP-based PFC to support lossless behavior for untagged traffic across Layer 3 connections to Layer 2 subnetworks for protocols such as Remote Direct Memory Access (RDMA) over converged Ethernet version 2 (RoCEv2).

With DSCP-based PFC, pause frames are generated to notify the peer that the link is congested based on a configured 6-bit Distributed Services code point (DSCP) value in the Layer 3 IP header of incoming traffic, rather than a 3-bit IEEE 802.1p code point in the Layer 2 VLAN header.

Because PFC can only send pause frames corresponding to PFC priority code points, the 6-bit configured DSCP value must be mapped to a 3-bit PFC priority to use in pause frames when DSCP-based PFC is triggered. Configuring the mapping involves mapping the PFC priority value to a no-loss forwarding class when you map the forwarding class to a queue, defining a congestion notification profile to enable PFC on traffic with the desired DSCP value, and configuring a DSCP classifier to associate the PFC priority-mapped forwarding class (along with the loss priority) with the configured DSCP value on which to trigger PFC pause frames.

The peer device should have output PFC and a corresponding flow control queue configured to match the PFC priority configuration on the device.

To configure DSCP-based PFC:

  1. (PTX10000 Series routers only) PTX10000 Series routers have separate buffer spaces for lossy and lossless queues, with 10percent of the total buffer spaces reserved for lossless queues by default. If necessary, adjust the amount of buffer space reserved for lossless queus.
    You adjust the percent of buffer space reserved for lossless queues on a per-FPC basis:
  2. Map a lossless forwarding class to a PFC priority—a 3-bit value represented in decimal form (0-7)—to use in the PFC pause frames.

    You must also assign an output queue to the forwarding class with the queue-num option. The no-loss option is required in this case to support lossless behavior for DSCP-based PFC, and the pfc-priority statement specifies the priority value mapping, as follows:

  3. Define an input congestion notification profile to enable PFC on traffic specified by the desired 6-bit DSCP value. Optionally configure the maximum receive unit (MRU) and cable length (used to determine PFC buffer headroom space reserved for the link):
    Note:

    You cannot configure both DSCP-based PFC and IEEE 802.1p PFC under the same congestion notification profile.

    (PTX10000 Series routers only) Include the PFC account(s) and assign a PFC account to each code point.

  4. Set up a DSCP classifier for the configured DSCP value and no-loss forwarding class mapped in the previous steps:
  5. Assign the classifier and congestion notification profile set up in the previous steps to an interface on which you are enabling DSCP-based PFC:
  6. Verify the configuration.
    1. Check the ingress port.
    2. Display the DSCP-based input congestion notification profile.
    3. Display which forwarding classes are mapped to each PFC priority.

For example, with the following sample commands configuring DSCP-based PFC for interface xe-0/0/1, PFC pause frames will be generated with PFC priority 3 when incoming traffic with DSCP value 110000 becomes congested:

(PTX10000 Series routers only) For example, with the following sample commands configuring DSCP-based PFC for interface xe-0/0/1, PFC pause frames will be generated with PFC priority 3 when incoming traffic with DSCP value 110000 reaches a delay equal to XOFF, which is set to 5000 microseconds, and a resume frame is sent with the delay falls back below XON, which is set to 2500 microseconds:

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