Reference Guide

Version Description
9.2(1.0) Introduced on the Z9500.
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 ExaScale.
6.5.1.9/7.4.1.0 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.
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.
Changes in the flow-control values may not be reflected automatically in the show interface output.
As a workaround, apply the new settings, execute shut then no shut on the interface, then check the
running-config of the port using the show interface command.
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:
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.
NOTE: If you use the disable rx flow control command, Dell Networking recommends
rebooting the system.
Example
Dell(conf-if-te-0/1)#show config
!
interface TengigabitEthernet 0/1
no ip address
switchport
no negotiation auto
flowcontrol rx off tx on
no shutdown
...
Interfaces 627