What Is Flow Control; What Is Priority-Based Flow Control - Dell PowerEdge M420 Configuration Manual

Table 24-1. Port-Based Traffic Control Features
Feature
Protected ports
LLPF

What is Flow Control?

IEEE 802.3x flow control allows nodes that transmit at slower speeds to
communicate with higher speed switches by requesting that the higher speed
switch refrains from sending packets. Transmissions are temporarily halted to
prevent buffer overflows. Enabling the flow control feature allows
PowerConnect M6220, M6348, M8024, and M8024-k switches to receive
pause frames from connected devices.
Flow control is available for ports that are configured for full-duplex mode of
operation. Since ports set to auto negotiate may not be added as LAG
members, LAG member ports cannot have flow control configured to auto.
Flow control is incompatible with head of line (HOL) blocking prevention
mode. The switch can operate in either mode, but not at the same time. If
flow control is enabled, HOL blocking is disabled.

What is Priority-Based Flow Control?

NOTE:
PFC is supported only on the PCM8024-k. The PCM6220, PCM6348, and
PCM8024 switches do not support PFC.
Ordinarily, when flow control is enabled on a physical link, it applies to all
traffic on the link. When congestion occurs, the hardware sends pause frames
that temporarily suspend traffic flow to help prevent buffer overflow and
dropped frames.
PFC provides a means of pausing individual priorities within a single physical
link. By pausing the congested priority or priorities independently, protocols
that are highly loss-sensitive can share the same link with traffic that has
different loss tolerances.
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Configuring Port-Based Traffic Control
Description
Prevents traffic from flowing between members of the same
protected port group.
Filters proprietary protocols that should not normally be relayed
by a bridge.