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Configuring Priority-Based Flow Control
PFC provides a flow control mechanism based on the 802.1p priorities in converged Ethernet traffic received on an interface
and is enabled by default when you enable DCB.
As an enhancement to the existing Ethernet pause mechanism, PFC stops traffic transmission for specified priorities (Class of
Service (CoS) values) without impacting other priority classes. Different traffic types are assigned to different priority classes.
When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the traffic that is
to be stopped. Data Center Bridging Exchange protocol (DCBx) provides the link-level exchange of PFC parameters between
peer devices. PFC allows network administrators to create zero-loss links for Storage Area Network (SAN) traffic that requires
no-drop service, while retaining packet-drop congestion management for Local Area Network (LAN) traffic.
To ensure complete no-drop service, apply the same dcb-map on all PFC and ETS enabled interfaces.
1. Create a DCB map to apply priority based flow control or enhanced transmission selection for specified priority groups and
priorities.
CONFIGURATION mode
dcb-map map-name
The maximum is 32 alphanumeric characters.
2. Configure the priority group with PGID, bandwidth percentage or strict priority for ETS and PFC mode.
DCB-MAP mode
priority-group pg_num [bandwidth percentage | strict-priority] pfc [on | off]
pg_num range is from 0 to 7.
bandwidth percentage range is from 1 to 100.
Either strict-priority or bandwidth percentage can be set for ETS on the priority group.
PFC can either be enabled or disabled for the priority group.
3. Configure the priorities to priority group.
DCB-MAP mode
priority-pgid <pgid> <pgid> <pgid> <pgid> <pgid> <pgid> <pgid> <pgid>
pgid range is from 0 to 7.
Configure priority to priority group mapping from priority 0 to priority 7 in order.
4. Exit the DCB MAP configuration mode.
DCB-MAP mode
exit
5. Enter interface configuration mode.
CONFIGURATION mode
interface type slot/port
6. Apply the dcb-map with PFC and ETS configurations to both ingress and egress interfaces.
INTERFACE mode
dcb-map map-name
7. Repeat steps 1 to 6 on all PFC and ETS enabled interfaces to ensure lossless traffic service.
NOTE:
All these configurations are available only in PMUX mode and you cannot perform these configurations in
Standalone mode.
Dell Networking OS Behavior: As soon as you apply a DCB MAPwith PFC enabled on an interface, DCBx starts exchanging
information with PFC-enabled peers. The IEEE802.1Qbb, CEE, and CIN versions of PFC Type, Length, Value (TLV) are
supported. DCBx also validates PFC configurations that are received in TLVs from peer devices.
By applying a DCB MAP with PFC enabled, you enable PFC operation on ingress port traffic. To achieve complete lossless
handling of traffic, also enable PFC on all DCB egress ports or configure the dot1p priority-queue assignment of PFC priorities to
lossless queues.
To remove a DCB MAP, including the PFC and ETS configurations it contains, use the no dcb-map map-name command in
INTERFACE Configuration mode.
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Data Center Bridging (DCB)