Reference Guide

430 | Interfaces
www.dell.com | support.dell.com
Using Ethernet Pause Frames for Flow Control
Using Ethernet Pause Frames for Flow Control are supported on the S5000 switch.
Ethernet Pause Frames allow for a temporary stop in data transmission. A situation may arise where a
sending device may transmit data faster than a destination device can accept it. The destination sends a
PAUSE frame back to the source, stopping the sender’s transmission for a period of time.
An Ethernet interface starts to send pause frames to a sending device when the transmission rate of ingress
traffic exceeds the egress port speed. The interface stops sending pause frames when the ingress rate falls
to less than or equal to egress port speed.
The globally assigned 48-bit Multicast address 01-80-C2-00-00-01 is used to send and receive pause
frames. To allow full-duplex flow control, stations implementing the pause operation instruct the MAC to
enable reception of frames with destination address equal to this multicast address.
The PAUSE frame is defined by IEEE 802.3x and uses MAC Control frames to carry the PAUSE
commands. Ethernet pause frames are supported on full duplex only.
If a port is over-subscribed, Ethernet Pause Frame flow control does not ensure no-loss behavior.
Restriction: Ethernet Pause Frame flow control is not supported if PFC is enabled on an interface. For
information about how to disable PFC, see Configuring PFC and ETS in a DCB Map on page 284.
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.
Note: On the S5000, threshold settings are not supported for Ethernet Pause Frame flow control.
Command Syntax Command Mode Purpose
flowcontrol rx [off | on] tx [off | on] INTERFACE Control how the system responds to and
generates 802.3x pause frames on Ethernet
interfaces. Default: rx off tx off.
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.