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CoS Support on EVPN VXLANs

You can configure class of service (CoS) features on VXLAN interfaces. VXLAN traffic from different tenants traverses network boundaries over the same physical underlay network. To ensure fairness in the treatment of traffic for all tenants in the VXLAN, and to prioritize higher priority traffic, apply CoS features to the VXLAN interfaces.

Understanding CoS on VXLAN Interfaces

This section describes how classification and rewrite rules are applied to packets in a VXLAN instance. Figure 1 shows a simple VXLAN with two leaf nodes and one spine node.

Figure 1: Classifiers and Rewrite Rules on VXLANsClassifiers and Rewrite Rules on VXLANs

Refer to Figure 1 to understand the packet flow with DSCP/ToS fields in a VXLAN:

  1. CE 1 sends a packet with Layer3 DSCP/ToS bit programmed to the Leaf 1 node.

  2. Leaf 1 receives the original packet and appends the VXLAN header on top of the original packet. The outer VXLAN Layer3 header uses the original packet DSCP/Tos bit. You can create classifiers based on the original packet DSCP/802.1p bit. The ingress interface on the ingress leaf supports DSCP and 802.1p classifiers.

  3. If rewrite is configured on Leaf 1, the inner header will have the DSCP/802.1p bit set by CE 1 and the outer header will have the rewrite bit. Only DSCP rewrite rules are supported.

  4. The Spine node receives the VXLAN packet and can use ingress classification using these DSCP bits and forward the packet to the egress interface with the appropriate forwarding class.

  5. The Spine egress interface can rewrite these bits using rewrite rules. These Spine rewrite rules only affects the outer Layer3 DSCP field. The inner/original packet still holds the DSCP/802.1p bit that was set by CE 1.

  6. Leaf 2 receives the packet, processes the tunnel termination, and remove the outer VXLAN header.

  7. Leaf 2 classification and rewrite functionality works on the inner header.

  8. The original packet arrives on CE 2.

Note:

On the leaf nodes, if the packet is multicast, you can use multi-destination classification to create appropriate multicast classification and rewrite rules.

Configuring CoS on VXLAN Interfaces

This section shows sample configurations of classifiers and rewrite rules for the leaf and spine nodes in VXLAN using Figure 1 as a reference. You can create schedulers as normal for the classifiers on each node.

Sample configuration of classifiers and rewrite rules on Leaf 1.

  1. Create a classifier based on the original DSCP/ToS bits:
  2. Apply the classier to the ingress interface:
  3. Create a rewrite rule for the outer VXLAN DSCP/ToS bits:
  4. Apply the rewrite rule to the egress interface:

Sample configuration of classifiers and rewrite rules on the Spine.

  1. Create a classifier based on the outer VXLAN DSCP/ToS bits:

  2. Apply the classier to the ingress interface:

  3. Create a rewrite rule for the outer VXLAN DSCP/ToS bits:

  4. Apply the rewrite rule to the egress interface:

Sample configuration of classifiers and rewrite rules on Leaf 2.

  1. Create a classifier based on the original DSCP/ToS bits, as the VXLAN header is removed at tunnel termination before forwarding classes are applied:

  2. Apply the classier to the ingress interface:

  3. Create a rewrite rule for the original DSCP/ToS bits:

  4. Apply the rewrite rule to the egress interface:

To check the CoS configuration on one of the interfaces:

To check the queue statistics on one of the interfaces: