Brocade Communications Systems 6650 About XON and Xoff thresholds, 1G or 10G ports, 40G ports

2 Basic port parameter configuration

About XON and XOFF thresholds

An 802.3x PAUSE frame is generated when the buffer limit at the ingress port reaches or exceeds the port’s upper watermark threshold (XOFF limit). The PAUSE frame requests that the sender stop transmitting traffic for a period of time. The time allotted enables the egress and ingress queues to be cleared. When the ingress queue falls below the port’s lower watermark threshold (XON limit), an 802.3x PAUSE frame with a quanta of 0 (zero) is generated. The PAUSE frame requests that the sender resume sending traffic normally.

NOTE

In Brocade ICX 6650, you cannot change the default XON and XOFF values.

Each 1G , 10G, and 40G port is configured with a default total number of buffers as well as a default XOFF and XON threshold.

TABLE 9 XON and XOFF default thresholds ( Apply to both Jumbo or non-Jumbo mode)

Limit when Jumbo disabled / % of buffer limit

Limit when Jumbo enabled / % of buffer limit

1G or 10G ports

Total buffers	256	256
XOFF	192 (78%)	192 (78%)
XON	136 (56%)	136 (56%)
40G ports
Total buffers	960	960
XOFF	832 (87%)	832 (87%)
XON	720 (75%)	720 (75%)

Configuration notes and feature limitations for symmetric flow control

Note the following configuration notes and feature limitations before enabling symmetric flow control.

•Symmetric flow control is supported on Brocade ICX 6650 devices.

•Symmetric flow control is supported on all 1 Gbps, 10 Gbps, and 40 Gbps data ports.

•To use this feature, 802.3x flow control must be enabled globally and per interface on the Brocade ICX 6650 device. By default, 802.3x flow control is enabled, but can be disabled with the no flow-controlcommand.

•The following QoS features are not supported together with symmetric flow control:

-dynamic buffer allocation (CLI command qd-descriptorand qd-buffer)

-Buffer profiles (CLI command buffer-profileport-region) is not supported for scheduler profiles.

-DSCP-based QoS (CLI command trust dscp)

•Head of Line (HOL) blocking may occur when symmetric flow control is enabled. This means that a peer can stop transmitting traffic streams unrelated to the congestion stream.

38	Brocade ICX 6650 Administration Guide
	53-1002600-01