Users Guide

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 the switch.
The discard threshold should be larger than the buffer threshold so that the buffer holds at least hold at least three packets.
Enabling Pause Frames
Enable Ethernet pause frames flow control on all ports on a chassis or a line card. If not, the system may exhibit unpredictable
behavior.
NOTE
: Changes in the flow-control values may not be reflected automatically in the show interface output. As a
workaround, apply the new settings, execute shut then no shut on the interface, and then check the running-config of
the port.
NOTE: If you disable rx flow control, Dell Networking recommends rebooting the system.
The flow control sender and receiver must be on the same port-pipe. Flow control is not supported across different port-pipes.
To enable pause frames, use the following command.
• Control how the system responds to and generates 802.3x pause frames on 10 Gigabit line cards.
INTERFACE mode
flowcontrol rx [off | on] tx [off | on] [threshold {<1-2047> <1-2013> <1-2013>}]
– rx on: enter the keywords rx on to process the received flow control frames on this port.
– rx off: enter the keywords rx off to ignore the received flow control frames on this port.
– tx on: enter the keywords tx on to send control frames from this port to the connected device when a higher rate of
traffic is received.
– tx off: enter the keywords tx off so that flow control frames are not sent from this port to the connected device
when a higher rate of traffic is received.
– threshold: when you configure tx on, you can set the threshold values for:
* Number of flow-control packet pointers: the range is from 1 to 2047 (default = 75).
* Flow-control buffer threshold in KB: the range is from 1 to 2013 (default = 49KB).
* Flow-control discard threshold in KB: the range is from 1 to 2013 (default= 75KB)
Pause control is triggered when either the flow control buffer threshold or flow control packet pointer threshold is reached.
Configure the MTU Size on an Interface
If a packet includes a Layer 2 header, the difference in bytes between the link MTU and IP MTU must be enough to include the
Layer 2 header.
For example, for VLAN packets, if the IP MTU is 1400, the Link MTU must be no less than 1422:
1400-byte IP MTU + 22-byte VLAN Tag = 1422-byte link MTU
The MTU range is from 594 to 9216, with a default of 1554 IP MTU automatically configures.
The following table lists the various Layer 2 overheads in the Dell Networking OS and the number of bytes.
Interfaces 449