Reference Guide

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.
The flow control sender and receiver must be on the same port-pipe. Flow control is not supported
across different port-pipes.
To enable pause frames, use the following command.
• Control how the system responds to and generates 802.3x pause frames on 1 and 10Gig line cards.
INTERFACE mode
flowcontrol rx [off | on] tx [off | on] [threshold {<1-2047> <1-2013>
<1-2013>}]
– rx on: enter the keywords rx on to process the received flow control frames on this port.
– rx off: enter the keywords rx off to ignore the received flow control frames on this port.
– tx on: enter the keywords tx on to send control frames from this port to the connected device
when a higher rate of traffic is received.
– tx off: enter the keywords tx off so that flow control frames are not sent from this port to the
connected device when a higher rate of traffic is received.
– threshold: when you configure tx on, you can set the threshold values for:
Interfaces
441