Using Ethernet Pause Frames for Flow ControlEthernet pause frames and threshold settings are supported on the Dell Networking OS.Ethernet Pause Frames allow for a temporary stop in data transmission. A situation may arise where a sending device may transmitdata faster than a destination device can accept it. The destination sends a PAUSE frame back to the source, stopping the sender’stransmission 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 theegress 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-duplexflow control, stations implementing the pause operation instruct the MAC to enable reception of frames with destination addressequal 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 framesare 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.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 the show interface output. To display the change,apply the new flow-control setting, shutdown the interface using the shutdown command, enable the interface using the noshutdown command, and use the show interface command to verify the changes.Enabling Pause FramesEnable Ethernet pause frames flow control on all ports on a chassis or a line card. If not, the system may exhibit unpredictablebehavior.NOTE: Changes in the flow-control values may not be reflected automatically in the show interface output. As aworkaround, apply the new settings, execute shut then no shut on the interface, and then check the running-configof 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 the Ethernet ports.INTERFACE modeInterfaces 393
