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 a 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. The only configuration applicable to half duplex
ports is rx off tx off.
NOTE: If a port is over-subscribed, Ethernet Pause Frame flow control does not ensure no loss
behavior.
The following error message appears when trying to enable flow control when you already configured
half duplex: Can’t configure flowcontrol when half duplex is configure, config
ignored.
The following error message appears when trying to enable half duplex and flow control configuration is
on: Can’t configure half duplex when flowcontrol is on, config ignored.
Enabling Pause Frames
Enable Ethernet pause frames flow control on all ports on a chassis. If not, the system may exhibit
unpredictable behavior.
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. (also refer to iSCSI Optimization: Operation).
NOTE: After you disable DCB, if link-level flow control is not automatically enabled on an interface,
to enable flow control, manually shut down the interface (shutdown command) and re-enable it
(no shutdown command).
To enable pause frames, use the following command.
• Control how the system responds to and generates 802.3x pause frames on 10 Gig ports.
INTERFACE mode
flowcontrol rx [off | on] tx [off | on] [negotiate]
–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.
–negotiate: enable pause-negotiation with the egress port of the peer device. If the negotiate
command is not used, pause-negotiation is disabled. 40 gigabit Ethernet interfaces do not support
pause-negotiation.
The default is rx off.
426 Interfaces