Dell PowerEdge FN I/O Module Command Line Reference Guide 9.10(0.0)

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flowcontrol

Controls 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)

Full–Switch

Command History

Version	Description
9.9(0.0)	Introduced on the FN IOM.
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.

Example (partial)

Dell(conf-if-tengig-0/1)#show config
                                             !
                                             interface TenGigabitEthernet 0/1
                                             no ip address
                                             switchport
                                             no negotiation auto
                                             flowcontrol rx off tx on
                                             no shutdown
                                             ...

Example (Values)

This Example shows how the Dell Networking OS negotiates the flow control values between two Dell Networking chassis connected back-to-back using 1G copper ports.

Configured
                                             LocRxConf LocTxConf RemoteRxConf RemoteTxConf	
                                             off       off        off           off     
                                             off           on      
                                             on            off     
                                             on            on      
                                             
                                             off       on         off           off     
                                             off           on      
                                             on            off     
                                             on            on      
                                             
                                             on        off        off           off     
                                             off           on      
                                             on            off     
                                             on            on      
                                             
                                             on        on         off           off     
                                             off           on      
                                             on            off     
                                             on            on      
                                             
                                             LocNegRx LocNegTx RemNegRx RemNegTx
                                             off      off     off      off
                                             off      off     off      off
                                             off      off     off      off
                                             off      off     off      off
                                             
                                             off      off     off      off
                                             off      off     off      off
                                             off      on      on       off
                                             off      off     off      off
                                             
                                             off      off     off      off
                                             on       off     off      on
                                             on       on      on       on
                                             on       on      on       on
                                             
                                             off      off      off     off
                                             off      off      off     off
                                             on       on       on      on
                                             on       on       on      on

Related Commands

show running-config — displays the flow configuration parameters (non-default values only).