Brocade FastIron Ethernet Switch Administration Guide - Manual (Page 68)

Symmetric flow control addresses the requirements of a lossless service class in an Internet Small
Computer System Interface (iSCSI) environment. It is supported on FCX and ICX standalone units as
well as on all FCX and ICX units in a traditional stack.
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.
Each 1G, 10G, and 40G port is configured with a default total number of buffers as well as a default
XOFF and XON threshold. The defaults are different for 1G ports versus 10G or 40G ports. Also, the
default XOFF and XON thresholds are different for jumbo mode versus non-jumbo mode. The defaults
are shown in
About XON and XOFF thresholds .
XON and XOFF default thresholds TABLE 8
Limit when Jumbo disabled / % of buffer limit Limit when Jumbo enabled / % of buffer limit
1G ports
Total buffers 272 272
XOFF 240 / 91% 216 / 82%
XON 200 / 75% 184 / 70%
10G ports
Total buffers 416 416
XOFF 376 / 91% 336 / 82%
XON 312 / 75% 288 / 70%
40G ports
Total buffers 960 960
XOFF 832 (87%) 832 (87%)
XON 720 (75%) 720 (75%)
If necessary, you can change the total buffer limits and the XON and XOFF default thresholds. Refer
to
Changing the total buffer limits on page 70 and Changing the XON and XOFF thresholds on page
69, respectively.
Configuration notes and feature limitations for symmetric flow control
Note the following configuration notes and feature limitations before enabling symmetric flow control.
About XON and XOFF thresholds
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