Reference Guide

The following table lists the range for each transmission media.
Transmission
Media
MTU Range (in bytes)
Ethernet
594-9216 = link MTU
The IP MTU automatically configures.
Using Ethernet Pause Frames for Flow Control
Ethernet Pause Frames allow for a temporary stop in data transmission. A situation may arise where a sending device may
transmit data faster than a destination device can accept it. The destination sends a PAUSE frame back to the source, stopping
the sender’s transmission for a period of time.
An Ethernet interface starts to send pause frames to a sending device when the transmission rate of ingress traffic exceeds the
egress port speed. The interface stops sending pause frames when the ingress rate falls to less than or equal to egress port
speed.
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.
If a port is over-subscribed, Ethernet Pause Frame flow control does not ensure no-loss behavior.
Restriction: Ethernet Pause Frame flow control is not supported if PFC is enabled on an interface.
Control how the system responds to and generates 802.3x pause frames on Ethernet interfaces. The default is rx off tx off.
INTERFACE mode. flowcontrol rx [off | on] tx [off | on]
Where:
rx on: Processes the received flow control frames on this port.
rx off: Ignores the received flow control frames on this port.
tx on: Sends control frames from this port to the connected device when a higher rate of traffic is received.
tx off: Flow control frames are not sent from this port to the connected device when a higher rate of traffic is received.
Changes in the flow-control values may not be reflected automatically in show interface output. To display the change, apply
the new flow-control setting, perform a shutdown followed by a no shutdown on the interface, and then check re-display the
show interface output for the port.
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.
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Interfaces