Reference Guide
NOTE: Dell Networking does not recommend mapping all ingress traffic to a single queue when
using PFC and ETS. However, Dell Networking does recommend using Ingress traffic classification
using the service-class dynamic dot1p command (honor dot1p) on all DCB-enabled
interfaces. If you use L2 class maps to map dot1p priority traffic to egress queues, take into account
the default dot1p-queue assignments in the following table and the maximum number of two
lossless queues supported on a port (refer to Configuring Lossless Queues).
Although Dell Networking OS allows you to change the default dot1p priority-queue assignments
(refer to Setting dot1p Priorities for Incoming Traffic), DCB policies applied to an interface may
become invalid if you reconfigure dot1p-queue mapping. If the configured DCB policy remains
valid, the change in the dot1p-queue assignment is allowed.
dot1p Value in the
Incoming Frame
Egress Queue Assignment
0 2
1 0
2 1
3 3
4 4
5 5
6 6
7 7
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 input policy with the same pause time and
dot1p priorities on all PFC-enabled peer interfaces.
240
Data Center Bridging (DCB)