Users Guide

Version Description
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 ow 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 trac at a higher rate than it can process, the frames are stored in the port buer. As a
result, buer usage increases. When the buer usage reaches the value specied in the “pause-threshold”
argument, the port sends PAUSE frame to the connected link partner to stop sending the trac. Eventually this
reduces the buer usage. When the buer usage drops by the value specied in the “resume-threshold”, the port
again sends a PAUSE frame with 0 as wait-time. This results in resume of the paused trac ow.
Important Points to Remember
• Do not enable tx pause when buer carving is enabled. For information and assistance, consult Dell
Networking TAC.
• Speeds less than one Gig cannot be congured when the asymmetric ow control conguration 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 one Gig
(Symmetric).
NOTE: If you use the disable rx flow control command, Dell Networking recommends
rebooting the system.
NOTE: Dell Networking OS does not support mirroring of tx pause frames.
Example
Dell(conf-if-Gi-1/1)# show config
!
interface GigabitEthernet 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 ow 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
Interfaces 635