White Papers

You can configure the size of the PFC buffer for all switches in a stack or all port pipes on a specified stack unit by entering the
following commands on the master switch.
● Configure the PFC buffer for all switches in the stack.
CONFIGURATION mode
[no] dcb stack-unit all pfc-buffering pfc-port {1-56} pfc-queues {1-2}
By default, the PFC buffer is enabled on all ports on the stack unit.
● Configure the PFC buffer for all port pipes in a specified stack unit by specifying the port-pipe number, number of PFC-
enabled ports, and number of configured lossless queues.
CONFIGURATION mode
[no] dcb stack-unit stack-unit-id [port-set port-set-id] pfc-buffering pfc-ports {1-56}
pfc-queues {1-2}
Valid stack-unit IDs are 0 to 5.
The only valid port-set ID (port-pipe number) is 0.
Dell Networking OS Behavior:
To achieve lossless PFC operation, the PFC port count and queue number used for the reserved buffer size that is created must
be greater than or equal to the buffer size required for PFC-enabled ports and lossless queues on the switch.
For the PFC buffer configuration to take effect, you must reload the stack or a specified stack unit (use the reload command
at EXEC Privilege level).
If you configure the PFC buffer on all stack units, delete the startup configuration on both the master and standby, and reload
the stack, the new master (previously standby) generates the following syslog message for each stack unit when it boots up:
PFC_BUFFER_CONFIG_CHANGED is generated for all stack units.
Configuring Enhanced Transmission Selection
ETS provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged Ethernet traffic.
Different traffic types have different service needs. Using ETS, you can create groups within an 802.1p priority class to
configure different treatment for traffic with different bandwidth, latency, and best-effort needs.
For example, storage traffic is sensitive to frame loss; interprocess communication (IPC) traffic is latency-sensitive. ETS allows
different traffic types to coexist without interruption in the same converged link by:
● Allocating a guaranteed share of bandwidth to each priority group.
● Allowing each group to exceed its minimum guaranteed bandwidth if another group is not fully using its allotted bandwidth.
To configure ETS and apply an ETS dcb-map to an interface, you must follow the steps described in Configuring Priority-Based
Flow Control.
How Enhanced Transmission Selection is Implemented
Enhanced transmission selection (ETS) provides a way to optimize bandwidth allocation to outbound 802.1p classes of
converged Ethernet traffic. Different traffic types have different service needs. Using ETS, groups within an 802.1p priority
class are auto-configured to provide different treatment for traffic with different bandwidth, latency, and best-effort needs.
For example, storage traffic is sensitive to frame loss; interprocess communication (IPC) traffic is latency-sensitive. ETS allows
different traffic types to coexist without interruption in the same converged link.
NOTE: The IEEE 802.1Qaz, CEE, and CIN versions of ETS are supported.
ETS is implemented on an Aggregator as follows:
● Traffic in priority groups is assigned to strict-queue or WERR scheduling in a dcb-map and is managed using the ETS
bandwidth-assignment algorithm. Dell Networking OS de-qeues all frames of strict-priority traffic before servicing any other
queues. A queue with strict-priority traffic can starve other queues in the same port.
● ETS-assigned bandwidth allocation and scheduling apply only to data queues, not to control queues.
● Dell Networking OS supports hierarchical scheduling on an interface. Dell Networking OS control traffic is redirected to
control queues as higher priority traffic with strict priority scheduling. After control queues drain out, the remaining data
traffic is scheduled to queues according to the bandwidth and scheduler configuration in the dcb-map. The available
bandwidth calculated by the ETS algorithm is equal to the link bandwidth after scheduling non-ETS higher-priority traffic.
Data Center Bridging (DCB)
235