Users Guide

Version Description
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
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 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
• Dell Networking OS only supports rx on tx on and rx off tx off for speeds less than 1 Gig
(Symmetric).
NOTE: If you use the disable rx flow control command, Dell Networking recommends
rebooting the system.
Example
Dell(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 (Values)
This Example shows how 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
Interfaces 691