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 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] monitor session-ID
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.
monitor session-ID: Enables mirror flow control frames on this port.
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.
Threshold Settings
When the transmission pause is set (tx on), you can set three thresholds to define the controls more closely. Ethernet pause frames
flow control can be triggered when either the flow control buffer threshold or flow control packet pointer threshold is reached.
The following thresholds are provided:
• Number of flow-control packet pointers: from 1 to 2047 (default = 75)
• Flow-control buffer threshold in KB: from 1 to 2013 (default = 49KB)
460
Interfaces