Understanding CoS on OVSDB-Managed VXLAN Interfaces

Classifier and Rewrite Rule Interface Support

The switch Ethernet ports can function as:

• Layer 2 physical interfaces (family ethernet-switching)

• Layer 2 logical interfaces (family ethernet-switching)

• Layer 3 physical interfaces (family inet/inet6)

• Layer 3 logical interfaces (family inet/inet6)

You can apply CoS classifiers and rewrite rules only to the following interfaces:

• Layer 2 physical interfaces. All underlying logical Layer 2 interfaces on the physical interface use the classifier and rewrite rule configuration on the physical interface. All OVSDB-managed VXLAN traffic on the interface uses the same Layer 2 CoS classifiers and rewrite rules.

• Layer 3 physical interfaces if at least one logical Layer 3 interface is configured on the physical interface. All underlying logical Layer 3 interfaces on the physical interface use the classifier and rewrite rule configuration on the physical interface. All OVSDB-managed VXLAN traffic on the interface uses the same Layer 3 CoS classifiers and rewrite rules.

Table 1 shows on which interfaces you can configure and apply classifiers and rewrite rules on network-facing interfaces.

Classifiers on OVSDB-Managed VXLAN Interfaces

Classifiers map incoming packets to a CoS service level, based on the code points in the header of the incoming packet. At the ingress interface, the switch reads the code point value in the packet header, then assigns the packet to the forwarding class and loss priority mapped to that code point value. The forwarding class is mapped to an egress queue and to scheduling properties. OVSDB-managed VXLAN interfaces support packet classification based on DSCP code points on all ingress interfaces, and packet classification based on DSCP multi-field (MF DSCP) code points or for behavior aggregate (BA) classification, the DSCP, DSCP IPv6, or IP precedence bits of the IP header convey the behavior aggregate class information on access-facing interfaces.

If you do not configure classifiers, the switch uses the default CoS settings to classify incoming traffic, as described in Understanding Default CoS Scheduling and Classification.

Classifier configuration on an OVSDB-managed VXLAN switch interface is similar to classifier configuration on any other type of ingress interface (see Understanding CoS Classifiers). However, on OVSDB-managed VXLAN interfaces, there is a difference in the way you can apply classifiers to Layer 2 interfaces compared to non-VXLAN interfaces. On OVSDB-managed VXLAN interfaces, you apply classifiers to Layer 2 physical interfaces, and the underlying logical interfaces use the classifier configuration applied on the physical interface. On non-VXLAN interfaces, you apply Layer 2 classifiers to logical interface unit 0 (all other logical interfaces on the port use the classifier configured on unit 0), and not to physical interfaces.

• Classifiers on Access-Facing Interfaces
• Classifiers on Network-Facing Interfaces

Rewrite Rules on OVSDB-Managed VXLAN Interfaces

When packets exit a network, edge switches might need to change the CoS settings of the packets. Rewrite rules change the value of the code points in the packet header by rewriting the code points to a different value in the outgoing packet. See Understanding CoS Rewrite Rules for detailed information about rewrite rules.

On OVSDB-managed VXLAN interfaces, you can apply DSCP rewrite rules to packets on network-facing physical interfaces. You cannot apply rewrite rules to access-facing OVSDB-managed VXLAN interfaces, and you cannot apply rewrite rules to IEEE 802.1p code points on network-facing interfaces.

By default, before a packet exits the network-facing interface on the ingress switch, the switch copies the DSCP code points from the packet header into the VXLAN header, so the DSCP code points are not rewritten. The VXLAN header needs to contain the correct DSCP code points because the network-facing ingress port of the egress switch uses the DSCP code points in the VXLAN header to classify the incoming packets.

If you want to change the value of the DSCP code points before the switch transmits packets across the network to the egress switch, you can configure a DSCP rewrite rule and apply it to the egress (network-facing) interface on the ingress switch.

Schedulers on OVSDB-Managed VXLAN Interfaces

Packet scheduling (the allocation of port resources such as bandwidth, scheduling priority, and buffers) on OVSDB-managed VXLAN interfaces uses enhanced transmission selection (ETS) hierarchical port scheduling, the same as other interfaces on the switch.

ETS hierarchical port scheduling allocates port bandwidth to traffic in two tiers. ETS provides better port bandwidth utilization and greater flexibility to allocate port resources to forwarding classes (this equates to allocating port resources to output queues because queues are mapped to forwarding classes) and to groups of forwarding classes called forwarding class sets (fc-sets).

First, ETS allocates port bandwidth to fc-sets (also known as priority groups). Each fc-set consists of one or more forwarding classes that carry traffic that requires similar CoS treatment. The bandwidth each fc-set receives is then allocated to the forwarding classes in that fc-set. Each forwarding class is mapped to an output queue. The scheduling properties of a forwarding class are assigned to the queue to which the forwarding class is mapped. Traffic control profiles control the allocation of port bandwidth to fc-sets. Queue schedulers control the allocation of fc-set bandwidth to forwarding classes. See Understanding CoS Output Queue Schedulers, Understanding CoS Traffic Control Profiles, and Understanding CoS Hierarchical Port Scheduling (ETS) for detailed information about scheduling.