Dell Command Line Reference Guide for the S4048–ON System 9.14.2.8

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flowcontrol

Control how the system responds to and generates 802.3x pause flow control frames.

Syntax
flowcontrol {rx {off | on} tx {off | on} [negotiate | pause-threshold value | resume-offset value] | [monitor session-ID]}

To return to the default, use the no form of this command.

Parameters
rx on
Enter the keywords rx on to process the received flow control frames on this port.
NOTE: Flow-control packets are mirrored only when flow-control rx is enabled on an interface.
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.
pause-threshold
Enter the buffer threshold limit for generating PAUSE frames.
resume-offset
Enter the offset value for generating PAUSE frames to resume traffic.
negotiate
(Optional) Enter the keyword negotiate to enable the 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
monitor
Enter the keyword monitor then the session-ID to enable mirror flow control frames on the interface. The range is from 0 to 65535.
Defaults
rx on tx off
Command Modes
INTERFACE
Command History

This guide is platform-specific. For command information about other platforms, see the relevant Dell EMC Networking OS Command Line Reference Guide.

Version
Description
9.11(0.0)
Added support for monitor session.
9.10(0.1)
Introduced on the S6010-ON and S4048T-ON.
9.10(0.0)
Introduced on the S3148.
9.10(0.0)
Introduced on the S6100–ON.
9.8(2.0)
Introduced on the S3100 series.
9.8(1.0)
Introduced on the Z9100–ON.
9.8(0.0P5)
Introduced on the S4048-ON.
9.8(0.0P2)
Introduced on the S3048-ON.
9.7(0.0)
Introduced on the S6000-ON.
9.6.0.0
Added support for the negotiate feature on the S4810 and S4820T.
9.2(1.0)
Introduced on the Z9500.
9.0.2.0
Introduced on the S6000.
8.3.19.0
Introduced on the S4820T.
8.3.11.1
Introduced on the Z9000.
8.3.7.0
Introduced on the S4810.
8.1.1.0
Introduced on the E-Series.
6.5.1.9 and 7.4.1.0
Introduced on the E-Series.
7.8.1.0
Introduced on the C-Series and S-Series with the thresholds option.
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.

When a port receives traffic at a higher rate than it can process, the frames are stored in the port buffer. As a result, buffer usage increases. When the buffer usage reaches the value specified in the “pause-threshold” argument, the port sends PAUSE frame to the connected link partner to stop sending the traffic. Eventually this reduces the buffer usage. When the buffer usage drops by the value specified in the “resume-threshold”, the port again sends a PAUSE frame with 0 as wait-time. This results in resume of the paused traffic flow.

Important Points to Remember

  • Do not enable tx pause when buffer carving is enabled. For information and assistance, consult Dell EMC Networking TAC.
  • The only configuration applicable to half duplex ports is rx off tx off. The following error is returned:

    Can’t configure flowcontrol when half duplex is configure, config ignored

  • Half duplex cannot be configured when the flow control configuration is on (default is rx on tx on). The following error is returned:

    Can’t 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.
  • Speeds less than one Gig cannot be configured when the asymmetric flow control configuration is on. The following error is returned:

    Can’t configure speed <1G when Asymmetric flowcontrol is on, config ignored

  • Dell EMC Networking OS only supports rx on tx on and rx off tx off for speeds less than one Gig (Symmetric).
NOTE: If you use the disable rx flow control command, Dell EMC Networking recommends rebooting the system.
NOTE: Dell EMC Networking OS does not support mirroring of tx pause frames.
Example
DellEMC(conf-if-Te-1/1)# show config
!
interface TenGigabitEthernet 1/1
no ip address
switchport
no negotiation auto
flowcontrol rx off tx on
no shutdown
...
Example (Monitor Session)
DellEMC(conf-if-te-1/5)#show config
!
interface TenGigabitEthernet 1/5
 no ip address
 shutdown
flowcontrol monitor 5
Example (Values)

This Example shows how Dell EMC Networking OS negotiates the flow control values between two Dell EMC 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

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