Owner's Manual

Chapter 5. Configuring Slots and Ports on a Switch | 119
NETGEAR 8800 User Manual
• Advertise support for pause frames
• Respond to pause frames
• Do not transmit pause frames
• Autonegotiation disabled
• Do not advertise support for pause frames
• Do not respond to pause frames
• Do not transmit pause frames
• 10 Gbps ports for the NETGEAR 8800 series switch modules:
• Autonegotiation always disabled
• Do not advertise support for pause frames
• Respond to pause frames
• Do not transmit pause frames
Flow Control
As shown above, with autonegotiation enabled, NETGEAR 8800 series switches advertise
the ability to support pause frames. This includes receiving, reacting to (stopping
transmission), and transmitting pause frames. However, the switch does not actually transmit
pause frames unless it is configured to do so, as described below.
IEEE 802.3x flow control provides the ability to configure different modes in the default
behaviors. Ports can be configured to transmit pause frames when congestion is detected,
and the behavior of reacting to received pause frames can be disabled.
TX
You can configure ports to transmit link-layer pause frames upon detecting congestion. The
goal of IEEE 802.3x is to backpressure the ultimate traffic source to eliminate or significantly
reduce the amount of traffic loss through the network. This is also called lossless switching
mode.
The following limitations apply to the TX flow control feature:
• Flow control is applied on an ingress port basis which means that a single stream
ingressing a port and destined to a congested port can stop the transmission of other
data streams ingressing the same port which are destined to other ports.
• High volume packets destined to the CPU can cause flow control to trigger. This includes
protocol packets such as VRRP and OSPF.
• When flow control is applied to the fabric ports, there can be a performance limitation. For
example, a single 1G port being congested could backpressure a high-speed fabric port
and reduce its effective throughput significantly.
To configure a port to allow the transmission of IEEE 802.3x pause frames, use the following
command:
enable flow-control tx-pause ports