I would like to enable the jumbo frame support on my N5k for specific SCSI trafic.

I've read we can't do it per interface but only on the system itself :

policy-map type network-qos JUMBO_MTU
  class type network-qos class-default
    mtu 9216


system qos
  service-policy type network-qos JUMBO_MTU

But this enables jumbo frame on the whole switch. Can I identify the SCSI traffic on the policy-map so that it's applied just for the traffic I want?

And so the jumbo from other type of traffic would be processed normally ?


1 Answer 1


Yes you can, you just have to classify the traffic. Here is an example where we classify iSCSI into its own class. The class-default class will match any other traffic.

class-map type qos match-all iSCSI
  match protocol iscsi
  match cos 4

policy-map type qos POLICY-QOS
  class iSCSI
    set qos-group 3
  class class-fcoe
    set qos-group 1

class-map type network-qos iSCSI
  match qos-group 3

policy-map type network-qos JUMBO
  class type network-qos iSCSI
    mtu 9216
    pause no-drop
  class type network-qos class-fcoe
    pause no-drop
    mtu 2158
  class type network-qos class-default

system qos
  service-policy type network-qos JUMBO
  service-policy type qos input POLICY-QOS

Just an additional note, you should modify the classification to match your environment and requirements. You can classify based on other criteria as well such as IP address.

class-map type qos match-all iSCSI
  match access-group name PERMIT-ANY


N5K Configuration Guide

  • Thank you very much! I don't understand all the commands but I will work on it. If you tell me that I can change MTU for iSCSI and doing noting for other traffic it's perfect
    – Jey10
    Commented Jan 20, 2017 at 13:30
  • Just an obvious question, as I read it, this system qos is applied on all FEX connected to the N5k ? Sorry but another question, does it hurt the cpu to add that on the system qos?
    – Jey10
    Commented Jan 20, 2017 at 13:31
  • It applies to all interfaces including FEX. I believe the QoS is done in hardware and shouldn't impact the CPU. I haven't seen any CPU increase on our N5Ks. I added a link to the N5K config guide that might be helpful.
    – John K.
    Commented Jan 20, 2017 at 16:14

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