Dell Force10 E300, Configuration Manual

Page: 451 / 1262

Interfaces | 451
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 destination address equal to this multicast address.
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
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.