Command Line Reference Guide

574 | Interfaces
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Command
History
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 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 S-Series. The
discard threshold should be larger than the buffer threshold so that the buffer holds at least hold at least
3 packets.
On 4-port 10G line cards: Changes in the flow-control values are not reflected automatically in the
show interface output for 10G interfaces. This issue results from the fact that 10G interfaces do not
support auto-negotiation per-se. On 1G interfaces, changing the flow control values causes an
automatic interface flap, after which PAUSE values are exchanged as part of the auto-negotiation
process. As a workaround, apply the new settings, execute shut followed by no shut on the interface,
and then check the running-config of the port.
Important Points to Remember
• Do not enable tx pause when buffer carving is enabled. Consult Dell Networking TAC for
information and assistance.
• 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
• Speeds less than 1 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
Version 8.1.1.0 Introduced on E-Series ExaScale
Version 6.5.1.9 and 7.4.1.0 Introduced on E-Series
Version 7.8.1.0 Introduced on C-Series and S-Series with thresholds
Note: The flow control must be off (rx off tx off) before configuring the half duplex.