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QOS on ISL ports

  • 1.  QOS on ISL ports

    Posted 02-05-2013 03:11 AM


    Following a number of issues we have had on an ISL that runs between to 48000 and a dcx, we have been told to disable QOS on the concerned ports.

    The ISL is formed from two links, so is a trunk.

    Is it best practice to disable QOS on ISL links?


  • 2.  Re: QOS on ISL ports

    Posted 02-05-2013 08:38 AM

    Hi there,

    QoS should be configured on the ISLs when you use QoS zones. If you're not using QoS zones, there is no need to configure QoS on the ISLs, since there are some VC reserved for QoS High and Low priority zones that are not used.




  • 3.  Re: QOS on ISL ports

    Posted 02-05-2013 12:30 PM

    I have ran into this issue before with ISL Links and was told by Brocade support to disable QoS on the ISL ports to prevent errors. One thing to keep in mind is that with ISL links it is best to keep them on the same ASIC on a blade when possible to prevent buffer credit to zero counters from incrementing on the ports.

    As has already been stated unless you are using QoS Zoning there is no need for QoS on your ISL ports.


  • 4.  Re: QOS on ISL ports

    Posted 02-26-2013 02:55 AM

    Thanks for the responses, we have been further advised to turn off credit recovery on the ISL ports, any thoughts on this?


  • 5.  Re: QOS on ISL ports

    Posted 03-12-2013 09:03 AM


    When there is a BB credit lost in a ISL, the only way to recover it back is to reset the port. And this is what Credit Recovery feature does. Without it, if you lose a BB credit (due to a physical issue for example) you wouldn't notice and the performance may be affected. I would not disable it unless there were a good reason to do it.