Reference Guide

444 | Interfaces
www.dell.com | support.dell.com
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.
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.
On the C-Series and 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 C-Series or S-Series system.
Note: On the C-Series and S-Series platforms, Ethernet Pause Frames TX should be enabled only after
consulting with the Dell Force10 Technical Assistance Center.
On 4-port 10G line cards: Changes in the flow-control values are not reflected automatically in the show
interface output for 10G interfaces. This issue results from the fact that 10G interfaces do not support
auto-negotiation per-se. On 1G interfaces, changing the flow control values causes an automatic interface flap,
after which PAUSE values are exchanged as part of the auto-negotiation process. As a workaround, apply the
new settings, execute shut followed by no shut on the interface, and then check the running-config of the port.