Reference Guide

show tdr tengigabitethernet <slot>/<port> EXEC Privilege Displays TDR test results.

Flow Control Using Ethernet Pause Frames

An Aggregator auto-congures to operate in auto-DCB-enable mode (Refer to Data Center Bridging: Auto-DCB-Enable Mode). In

this mode, Aggregator ports detect whether peer devices support converged enhanced Ethernet (CEE) or not, and enable DCBX

and PFC or link-level ow control accordingly:

• Interfaces come up with DCB disabled and link-level ow control enabled to control data transmission between the Aggregator

and other network devices.

• When DCB is disabled on an interface, PFC, ETS, and DCBX are also disabled.

• When DCBX protocol packets are received, interfaces automatically enable DCB and disable link level ow control.

• DCB is required for PFC, ETS, DCBX, and FCoE initialization protocol (FIP) snooping to operate.

Link-level ow control uses Ethernet pause frames to signal the other end of the connection to pause data transmission for a certain

amount of time as specied in the frame. 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.

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

ow control, stations implementing the pause operation instruct the MAC to enable reception of frames with a destination address

equal to this multicast address.

The pause frame is dened 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 conguration applicable to half duplex ports is rx o tx o.

Note that if a port is over-subscribed, Ethernet Pause Frame ow control does not ensure no loss behavior.

The following error message appears when trying to enable ow control when half duplex is already congured:

Can’t configure flowcontrol when half duplex is configure, config ignored.

The following error message appears when trying to enable half duplex and ow control conguration is on:

Can’t configure half duplex when flowcontrol is on, config ignored.

Enabling Pause Frames

Enable Ethernet pause frames ow control on all ports on a chassis. If not, the system may exhibit unpredictable behavior.

NOTE: If you disable rx flow control, Dell Networking recommends rebooting the system.

The ow control sender and receiver must be on the same port-pipe. Flow control is not supported across dierent port-pipes. (also

refer to iSCSI Optimization: Operation).

NOTE: After you disable DCB, if link-level ow control is not automatically enabled on an interface, to enable ow

control, manually shut down the interface (shutdown command) and re-enable it (no shutdown command).

To enable pause frames, use the following command.

• Control how the system responds to and generates 802.3x pause frames on 10 and 40 Gig ports.

INTERFACE mode

flowcontrol rx [off | on] tx [off | on] [negotiate]

– rx on: enter the keywords rx on to process the received ow control frames on this port.

– rx off: enter the keywords rx off to ignore the received ow control frames on this port.

Interfaces