Administrator Guide

flowcontrol
Control how the system responds to and generates 802.3x pause frames on 10G and 40Gig stack units.
Syntax
flowcontrol rx {off | on} tx {off | on} threshold
Parameters
rx on Enter the keywords rx on to process the received flow control frames on this
port. This is the default value for the receive side.
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. This is the default value on the
send side.
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.
Defaults
● rx off
● tx off
Command Modes INTERFACE
Supported Modes Programmable-Mux (PMUX)
Command
History
Version Description
9.4(0.0) Supported on the FN I/O Aggregator.
9.2(0.0) Introduced on the M I/O Aggregator.
8.3.16.1 Introduced on the MXL 10/40GbE Switch IO Module.
Usage
Information
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 the reception of frames with a destination address equal to this multicast address.
The pause:
● Starts when either the packet pointer or the buffer threshold is met (whichever is met first). When
the discard threshold is met, packets are dropped.
● 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 switch. The
discard threshold should be larger than the buffer threshold so that the buffer holds at least hold at least
three packets.
Important Points to Remember
● Do not enable tx pause when buffer carving is enabled. For information and assistance, consult Dell
Networking TAC.
● Asymmetric flow control (rx on tx off, or rx off tx on) setting for the interface port less
than 100 Mb/s speed is not permitted. The following error is returned:
Can’t configure Asymmetric flowcontrol when speed <1G, config ignored
● The only configuration applicable to half duplex ports is rx off tx off. The following error is
returned:
Cannot configure Asymmetric flowcontrol when speed <1G, config ignored>
● You cannot configure half duplex when the flow control configuration is on (default is rx on tx
on). The following error is returned: Cannot configure half duplex when flowcontrol
is on, config ignored
NOTE: The flow control must be off (rx off tx off) before configuring the half duplex.
168 Interfaces