CoS on Virtual Chassis Switch Ports

Similarities in CoS Support on Virtual Chassis Access Interfaces Compared to Standalone Device (or QFabric system Node device) Access Interfaces

Virtual Chassis access interfaces support the following CoS features in the same way as access interfaces on standalone devices and QFabric system Node devices:

• Forwarding classes—The default forwarding classes, queue mapping, and packet drop attributes (Table 1) are the same:

  Table 1: Default Forwarding Class Configuration

  Default Forwarding Class	Default Queue Mapping	Default Packet Drop Attribute
  best-effort (be)	0	drop
  fcoe	3	no-loss
  no-loss	4	no-loss
  network-control (nc)	7	drop
  mcast	8	drop

• Packet classification—Classifier default settings and configuration are the same. Support for behavior aggregate, multifield, multidestination, and fixed classifiers is the same.

• Enhanced transmission selection (ETS)—This data center bridging (DCB) feature that supports hierarchical scheduling has the same defaults and user configuration, including forwarding class set (priority group) and traffic control profile configuration.

• Priority-based flow control (PFC)—This DCB feature that supports lossless transport has the same defaults and user configuration, including support for six lossless priorities (forwarding classes).

• Ethernet PAUSE—This feature has the same defaults and configuration.

• Queue scheduling—This feature has the same defaults, configuration, and scheduler-to-forwarding-class mapping. Queue scheduling is a subset of hierarchical scheduling.

• Priority group (forwarding class set) scheduling—This feature has the same defaults and configuration. Priority group scheduling is a subset of hierarchical scheduling.

• WRED profiles—This feature has the same defaults and configuration.

• Code-point aliases—This feature has the same defaults and configuration.

• Rewrite rules—This feature has the same defaults and configuration (no default rewrite rules applied to egress traffic).

• Host outbound traffic—This feature has the same defaults and configuration.

Differences in CoS Support on Virtual Chassis Access Interfaces Compared to Standalone Device (or QFabric system Node device) Access Interfaces

The default shared buffer settings and the way in which you configure shared buffers are the same on Virtual Chassis access interfaces as on standalone and QFabric system Node devices. The difference is that on Virtual Chassis access interfaces, the shared buffer configuration is global and applies to all access ports on all members of the Virtual Chassis, while on standalone or QFabric system Node devices, you can configure different buffer settings on different access interfaces.

You cannot configure different shared buffer settings for different Virtual Chassis members. All members of a Virtual Chassis use the same shared buffer configuration.

Similarities in CoS Support on VCP Interfaces and QFabric System Node Device Fabric Interfaces

VCP interfaces support full hierarchical scheduling (ETS). ETS includes the following CoS features. VCP interfaces support no other CoS features.

• Creating forwarding class sets (priority groups) and mapping forwarding classes to forwarding class sets.

• Scheduling individual output queues. The scheduler defaults and configuration are the same as the scheduler on access interfaces.

• Scheduling priority groups (forwarding class sets) using a traffic control profile. The defaults and configuration are the same as on access interfaces.

The behavior of lossless traffic across 40-Gigabit VCP interfaces is the same as the behavior of lossless traffic across QFabric system Node device fabric ports. The system automatically enables flow control for lossless forwarding classes (priorities). The system dynamically calculates buffer headroom that is allocated from the global lossless-headroom buffer for the lossless forwarding classes on each 40-Gigabit VCP interface. If there is not enough global lossless-headroom buffer space to support the number of lossless flows on a 40-Gigabit VCP interface, the system generates a syslog message.

Differences in CoS Support on VCP Interfaces and QFabric System Node Device Fabric Interfaces

Although most of the CoS behavior on VCP interfaces is similar to CoS behavior on the fabric ports of QFabric system Node devices, there are some important differences:

• Hierarchical scheduling (queue and priority group scheduling)—On QFabric system Node device fabric interfaces, you can apply a different hierarchical scheduler (traffic control profile) to different priority groups (forwarding class sets) on different interfaces. However, on VCP interfaces, the schedulers that you apply to priority groups are global to all VCP interfaces. One hierarchical scheduler controls scheduling for a priority group on all VCP interfaces.

  You attach a scheduler to VCP interfaces using the global identifier (vcp-*) for VCP interfaces. For example, if you want to apply a traffic control profile (traffic control profiles contain both queue and priority group scheduling configuration) named vcp-hpc-tcp to a forwarding class set named vcp-hpc-fcset, you include the following statement in the configuration:

  The system applies the hierarchical scheduler vcp-hpc-tcp to the traffic mapped to the priority group vcp-hpc-fcset on all VCP interfaces.

• You cannot attach classifiers, congestion notification profiles, or rewrite rules to VCP interfaces. Also, you cannot configure buffer settings on VCP interfaces. Similar to QFabric system Node device fabric interfaces, you can only attach forwarding class sets and traffic control profiles to VCP interfaces.

• Lossless transport is supported only on 40-Gigabit VCP interfaces. If you break out a 40-Gigabit VCP interface into 10-Gigabit VCP interfaces, lossless transport is not supported on the 10-Gigabit VCP interfaces.