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What Are Flowcontrol Behaviours on EOS Switches?

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TitleWhat Are Flowcontrol Behaviours on EOS Switches?

Ethernet provides mechanisms to  prevent large amounts of traffic from causing network latency.
Wikipedia says,

Ethernet flow control is a mechanism for temporarily stopping the transmission of data on Ethernet family computer networks. The first flow control mechanism, the pause frame, was defined by the IEEE 802.3x standard.

The follow-on priority-based flow control, as defined in the IEEE 802.1Qbb standard, provides a link-level flow control mechanism that can be controlled independently for each Class of Service (CoS), as defined by IEEE P802.1p. The goal of this mechanism is to ensure zero loss under congestion in data center bridging (DCB) networks.

All EOS switches support flow  control, however,there are some differences  in implimentation  between the Securestack and other switches.
  • S-Series
  • K-Series
  • 7100-Series
  • G-Series
  • Securestack
On the  S-Series, K-Series, and 7100-Series, as long as Flow Control is advertised on the port level it will continue to function, even when disabled with set flow control disable.
Securestacks will not advertise pause frames if flow control is disabled  but Extreme recommends  that if flow control is disabled   globally advertisements of flow control should be cleared on a port level to  notify other switches pause frames are no longer being negotiated.

In either case, if all ports are auto-negotiating speed/duplex/flow control (this is the default condition); then instead of issuing the 'set flowcontrol disable command, consider issuing the command,
clear port advertise *.*.* pause 
the counters will stop accumulating because no local port is negotiating to advertise flow control

Type, show port advertise'  to verify no local port or linked device is participating in flow control. This method provides an ongoing view of what is happening with flow control, helps to increase the useable bandwidth by stopping pause frame transmission by peer devices, and allows the txqmonitor feature (as supported) to continue operating.
To disable Flow Control on  S-Series, K-Series and 7100-Series

set port flowcontrol <port#> both disable
clear port advertise <port#> bpause

To re-enable Flow Control on a port:
set port flowcontrol <port#> both enable
set port advertise <port#> bpause

Disable flow control on Securestacks  and G-Series

Disable flow control
set flowcontrol disable
Notify Neighbor switches that Flow Control is disabled by clearing advertisement on ports
clear port advertise *.*.* pause

To review the result, in either case:
show port flowcontrol <port#>
show port advertise <port#>

Flow Control - which uses IEEE 802.1x Pause frames - only applies to ports operating in
Full Duplex mode. Half Duplex ports, use collisions to control excessive or bursty traffic.

Flow Control should be disabled on  both  switches  on each end of the link
Disabling flow-control or clearing pause frame advertisement will cause a very short interruption in traffic and an STP topology change.
Additional notes



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