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I am very new to network engineering, I have read through the netgear user manual and find nothing about Global Flow Control (IEEE 802.3x) Mode. Is it different than the storm controls that I have the ability to change all or per interface?

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Ethernet Flow Control is different than Storm Control.

Ethernet Flow Control was developed because traffic on a link may be generated faster than the receiver can handle it. The IEEE has several efforts for this in 802.1 and 802.3. Unfortunately, this really doesn't help with STP loops.

Storm Control is something which some switch vendors have implemented, and it is typically used to limit broadcast and multicast traffic to acceptable levels in order to mitigate STP loops. Cisco does have an implementation for unicast traffic, too.

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  • So if I understand you correctly, they are almost the same but Ethernet Flow Control is not reliable when controlling STP loops which storm control can now reliably control? Does storm control also send pause frames to control the situation? I am working with a switch that has Global Flow control, unicast/broadcast/multicast storm control. – user_ABCD Dec 15 '15 at 17:41
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    No, they were designed for different reasons. It is possible that one or more devices on one end of a link can transmit more frames that a device on the other end of the link can handle. That is the case for Ethernet Flow control. Storm Control was designed to handle storms which are typically caused by STP loops, but you may want to control the number of broadcasts or multicasts for other reasons, too. – Ron Maupin Dec 15 '15 at 17:45
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If I understand this correctly, "Ethernet Flow control" is used when one computer on a single Ethernet network segment can not cope with the rate that pockets are being sent to it.

"Ethernet Flow control" is blocked by switches (bridges), so does not effect what happens on any other Ethernet network that is connected to the switch.

These days, it is uncommon to find a "Ethernet network segment" that consists of more then one computer and one switch port. In the "old days" there used to be lots of computers on each network segment, sharing the same wire.

(Storm Control is well explained by Ron.)

In real life, most flow control is done by the TCP protocol and network buffers are large enough that "low level" flow control is not really needed to the extent it was when I was a child and Ethernet run on yellow cables the thickness of my finger.

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