Reference Guide

Control how the system responds to and generates 802.3x pause frames on Ethernet interfaces. The
default is rx off tx off. INTERFACE mode. flowcontrol rx [off | on] tx [off | on]
Where:
rx on: Processes the received flow control frames on this port.
rx off: Ignores the received flow control frames on this port.
tx on: Sends control frames from this port to the connected device when a higher rate of traffic is
received.
tx off: Flow control frames are not sent from this port to the connected device when a higher rate of
traffic is received.
Changes in the flow-control values may not be reflected automatically in show interface output. To
display the change, apply the new flow-control setting, perform a shutdown followed by a no shutdown
on the interface, and then check re-display the show interface output for the port.
Threshold Settings
Threshold settings are supported on the S4820T platform.
When the transmission pause is set (tx on), you can set three thresholds to define the controls more
closely. Ethernet pause frames flow control can be triggered when either the flow control buffer
threshold or flow control packet pointer threshold is reached. The thresholds are:
• Number of flow-control packet pointers: from 1 to 2047 (default = 75)
• Flow-control buffer threshold in KB: from 1 to 2013 (default = 49KB)
• Flow-control discard threshold in KB: from 1-2013 (default= 75KB)
The pause is started when either the packet pointer or the buffer threshold is met (whichever is met first).
When the discard threshold is met, packets are dropped.
The pause ends when both the packet pointer and the buffer threshold fall below 50% of the threshold
settings.
The discard threshold defines when the interface starts dropping the packet on the interface. This may be
necessary when a connected device does not honor the flow control frame sent by the S4820T.
The discard threshold should be larger than the buffer threshold so that the buffer holds at least hold at
least three packets.
Enabling Pause Frames
Enable Ethernet pause frames flow control on all ports on a chassis or a line card. If not, the system may
exhibit unpredictable behavior.
NOTE: Changes in the flow-control values may not be reflected automatically in the show
interface output. As a workaround, apply the new settings, execute shut then no shut on the
interface, and then check the running-config of the port.
NOTE: If you disable rx flow control, Dell Networking recommends rebooting the system.
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Interfaces