Users Guide

Changes in the flow-control values may not be reflected automatically in the show interface output. To
display the change, apply the new flow-control setting, shutdown the interface using the shutdown
command, enable the interface using the no shutdown command, and use the show interface command
to verify the changes.
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 the Ethernet ports.
INTERFACE mode
flowcontrol rx [off | on] tx [off | on] [negotiate]
• 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.
• negotiate: enable pause-negotiation with the egress port of the peer device. If the negotiate
command is not used, pause-negotiation is disabled. 40 gigabit Ethernet interfaces do not support
pause-negotiation.
• 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).
• Buffer threshold limit for generating PAUSE frames: the range is from 1 to 4096.
• Offset value for generating PAUSE frames to resume traffic: the range is from 1 to 4096.
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:
Interfaces 406