Thursday, March 27, 2014

Enabling Jumbo Frames on a Cisco Nexus 3548

In this blog we will demostrate a basic network-qos policy type  for enabling support of jumbo frames in a nexus switch.


1st, The switch model and software

system:    version 6.0(2)A1(1b)
cisco Nexus 3548 Chassis ("48x10GE Supervisor")


To enable jumbo frames you first need to build a policy. The name of the policy can be anything that you want it to be.

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



After you have defined the policy-map you can now activate it via the following ;


system qos
  service-policy type network-qos jumboframes


To monitor the changes we issues the following commands ;


HETYSW2# show queuing interface ether 1/12 | grep MTU
    HW MTU: 9216 (9216 configured)

HETYSW2#

We can also look at the interface counters, but  I believe the switch  doesn't report packets bigger than 1548 bytes;


e.g


show int eth 1/12  counters  detailed
Ethernet1/12
  Rx Packets:                                    99810475
  Rx Unicast Packets:                            99567164
  Rx Multicast Packets:                            244586
  Rx Broadcast Packets:                               108
  Rx Bytes:                                   10238006362
  Rx Packets from 0 to 64 bytes:                  1111204
  Rx Packets from 65 to 127 bytes:               75378834
  Rx Packets from 128 to 255 bytes:              14313107
  Rx Packets from 256 to 511 bytes:               2618278
  Rx Packets from 512 to 1023 bytes:              2467560
  Rx Packets from 1024 to 1518 bytes:             2493491
  Rx Packets from 1519 to 1548 bytes:             1429384  
<------HERE

   Tx Packets:                                   116271700
  Tx Unicast Packets:                           115850055
  Tx Multicast Packets:                            421292
  Tx Broadcast Packets:                               353
  Tx Bytes:                                   16564798171
  Tx Packets from 0 to 64 bytes:                 16577055
  Tx Packets from 65 to 127 bytes:               68013570
  Tx Packets from 128 to 255 bytes:              21122812
  Tx Packets from 256 to 511 bytes:               3376787
  Tx Packets from 512 to 1023 bytes:              3864588
  Tx Packets from 1024 to 1518 bytes:             3295462
  Tx Packets from 1519 to 1548 bytes:               21426   <------HERE


and


show int eth 1/12  counters   errors

--------------------------------------------------------------------------------
Port          Align-Err    FCS-Err   Xmit-Err    Rcv-Err  UnderSize OutDiscards
--------------------------------------------------------------------------------
Eth1/12                0          0          0          0          0           0

--------------------------------------------------------------------------------
Port         Single-Col  Multi-Col   Late-Col  Exces-Col  Carri-Sen       Runts
--------------------------------------------------------------------------------
Eth1/12                0          0          0          0          0           0

--------------------------------------------------------------------------------
Port          Giants SQETest-Err Deferred-Tx IntMacTx-Er IntMacRx-Er Symbol-Err
--------------------------------------------------------------------------------
Eth1/12             0          --           0           0           0          0



Alternatively  you can review the  network-qos policy-map to confirm  mtu sizes the default and current size are shown ;


show policy-map  type network-qos


  Type network-qos policy-maps
  ===============================

  policy-map type network-qos jumboframes
    class type network-qos class-default

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

      mtu 1500
 

Ken Felix
Freelance Network / Security Engineer
kfelix  ----a---t---socpuppets ---d---o---t---com

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4 comments:

  1. Awesome,
    And is this all? All my interfaces will be forwarding Jumboframes? My config is for a Storage and they need the half of the interfaces working without jumbframes.

    ReplyDelete
  2. This only enables the interface to accept jumbo frame.

    ReplyDelete
  3. Yeap only the layer2 interface. If you have a SVI you still need to enable mtu setting and a lot of the non 7K still will not allow you to set the interface MTU.


    e.g

    config t

    int vlan 44
    mtu 9126
    end

    Without the fabric being made aware of the jumbo frames, you can't run any SVIs at a larger ethernet frame.

    ReplyDelete
  4. how to you apply this on the interface? does it apply to ALL interfaces or is it 1x1? thx

    ReplyDelete