Reference Guide

Interfaces | 365
The PAUSE frame is defined by IEEE 802.3x and uses MAC Control frames to carry the PAUSE
commands. Ethernet Pause Frames are supported on full duplex only. The only configuration applicable to
half duplex ports is
rx off tx off.
Note that if a port is over-subscribed, Ethernet Pause Frame flow control does not ensure no
loss behavior.
The following error message appears when trying to enable flow control when half duplex is
already configured: Can’t configure flowcontrol when half duplex is configure, config ignored.
The following error message appears when trying to enable half duplex and flow control
configuration is on: Can’t configure half duplex when flowcontrol is on, config ignored.
Threshold Settings
Threshold Settings are supported only on platforms: c s z
When the transmission pause is set (tx on), 3 thresholds can be set to define the controls more closely.
Ethernet Pause Frames flow control can be triggered when either the flow control buffer threshold or flow
control packet pointer threshold is reached. The thresholds are:
• Number of flow-control packet pointers: 1-2047 (default = 75)
• Flow-control buffer threshold in KB: 1-2013 (default = 49KB)
• Flow-control discard threshold in KB: 1-2013 (default= 75KB)
The pause is started when
either the packet pointer or the buffer threshold is met (whichever is met first).
When the discard threshold is met, packets are dropped.
The pause 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 doesn’t honor the flow control frame sent by S-Series.
The discard threshold should be larger than the buffer threshold so that the buffer holds at least hold at least
3 packets.
Enable Pause Frames
Ethernet Pause Frames flow control must be enabled on all ports on a chassis or a line card. If not, the
system may exhibit unpredictable behavior.
Note: On the C-Series and S-Series (non-S4810) platforms, Ethernet Pause Frames TX should be
enabled only after consulting with the Dell Force10 Technical Assistance Center.
Note: The S4810 supports only the rx control option. The S4810 does not transmit pause frames.