Reference Guide

Interfaces | 421
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 multi-cast 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. Consult Dell Force10TAC for information
and assistance.
• 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
• FTOS only supports rx on tx on and rx off tx off for speeds less than 1 Gig (Symmetric).
• On the S-Series systems, the flow-control sender and receiver must be on the same port-pipe. Flow
control is not supported across different port-pipes on the S-Series system.
Example
Figure 20-2. show running config (partial)
FTOS(conf-if-gi-0/1)#show config
!
interface GigabitEthernet 0/1
no ip address
switchport
no negotiation auto
flowcontrol rx off tx on
no shutdown...
Version 9.0.2.0 Introduced on then S6000.
Version 8.3.11.1 Introduced on the Z9000.
Version 8.2.1.0 Introduced on the S4810
Note: The flow control must be off (rx off tx off) before configuring the half duplex.