Users Guide

Transmission
Media
MTU Range (in bytes)
Ethernet
The MTU range is from 594 to 9216, with a default of 1554.
The IP MTU automatically congures.
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 trac 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 ow
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 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.
If a port is over-subscribed, Ethernet Pause Frame ow control does not ensure no-loss behavior.
Restriction: Ethernet Pause Frame ow 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 o tx o. INTERFACE
mode. flowcontrol rx [off | on] tx [off | on] monitor session-ID
Where:
rx on: Processes the received ow control frames on this port.
rx off: Ignores the received ow control frames on this port.
tx on: Sends control frames from this port to the connected device when a higher rate of trac is received.
tx off: Flow control frames are not sent from this port to the connected device when a higher rate of trac is received.
monitor session-ID: Enables mirror ow control frames on this port.
Changes in the ow-control values may not be reected automatically in show interface output. To display the change, apply the new ow-
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.
Threshold Settings
When the transmission pause is set (tx on), you can set three thresholds to dene the controls more closely. Ethernet pause frames ow
control can be triggered when either the ow control buer threshold or ow control packet pointer threshold is reached.
The following thresholds are provided:
• Number of ow-control packet pointers: from 1 to 2047 (default = 75)
• Flow-control buer threshold in KB: from 1 to 2013 (default = 49KB)
Interfaces
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