Ethernet Switches & Routers

Occasional Contributor
Posts: 12
Registered: ‎03-26-2013

Symmetric flow control on FCX stacked devices causes data loss on stack ports

Hi all!


About three month ago I enabled symmetric flow control on FCX stack of 8 units, due to recommendations for iSCSI support (jumbo also enabled). Everything worked fine, before the network grown and traffic flows raised. The whole stack started degrading performance, we observed about 50% packet loss and jitter 200-500msec. The we noticed errors on command "show stack conn" stating that there are only one-directional cpu connectivity on some units, somtetimes the command did not produce errors. Either we noticed raising InDiscards errors counter on all of the stacking ports.

After two weeks of diagnostics, I conditionally tried to disable symmetric flow control, just by chance, becuase it was the only difference in config from another, working FCX stack. After this, network operated normal, with no InDiscards raising on stack ports.

So we expected some part of this behavior on normal data ports due to flow control mechanics, but why it also affect stack ports, but should as I understand the purpose of this feature.

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