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Juniper MX maximum MTU

  • 1.  Juniper MX maximum MTU

    Posted 07-03-2017 10:23

    Hello All, hope you are doing well.

     

    I was checking the maximum MTU I can configure in a MX960 and it was 9192, but in a EX4200 it's 9216. Why the 24 bytes difference?

     

    Most importantly, if a customer wants a VPLS/L3VPn with 9200+ MTU in our MX960 MPLS network, why isn't it possible? I haven't been able to find any detailed documentation about this, I was hoping someone could help me or point me in the right direction.

     

    I attach the outputs and the FPC/PIC/Xcvr information:

     

    mx960# set interfaces et-X/X/X mtu ?
    Possible completions:
    <mtu> Maximum transmit packet size (256..9192)

     

    MPC5E 3D 2CGE+4XGE / 1X100GE CFP2 OTN / CFP2-100G-LR4

     

    ex4200-24f# set interfaces ge-X/X/X mtu ?
    Possible completions:
    <mtu> Maximum transmit packet size (256..9216)

     

    EX4200-24F / 24x 100 Base-FX/1000 Base-X / SFP-LX10

     

    Thank you for your help!



  • 2.  RE: Juniper MX maximum MTU

    Posted 07-04-2017 03:12

    Hello,


    @aarriola wrote:

     

    I was checking the maximum MTU I can configure in a MX960 and it was 9192, but in a EX4200 it's 9216. Why the 24 bytes difference?

     

     


    Usually max MTU is one of chipset characteristics and EX4200 / MX use different chipsets.

     


    @aarriola wrote:

     

    Most importantly, if a customer wants a VPLS/L3VPn with 9200+ MTU in our MX960 MPLS network, why isn't it possible? 


    It is possible, just not on this particular Juniper hardware. Juniper MX MPC7 & later have max MTU ~16K bytes - they use next incarnation of Trio chipset called "Eagle".

    HTH

    Thx

    Alex



  • 3.  RE: Juniper MX maximum MTU

    Posted 07-04-2017 11:26

    Hello Alex. Thank you very much for taking the time to reply.

     

    I understand EX and MX have different chipsets and thus can have a different MTU. I believe my question could be: why would Juniper decide that a low end access/metro device (ex4200) has a chipset that can handle a higher MTU than the chipset of a high end core device (MX960). It doesn't make sense to me, but there probably is a good reason for it and I would like to know.

     

    Unfortunately our newest MPCs are 5, so we won't be able to deliver a 9200+ MTU, I wish there was a workaround. Thank you for the clarification!



  • 4.  RE: Juniper MX maximum MTU

    Posted 09-03-2017 12:36

    Hi aarriola ,

     

    For Junos OS 16.1R1 and later releases, the MTU size supported is 9,500 bytes on MPC5 cards.

     

    It is also documented in below URL.

     

    6x40GE + 24x10GE MPC5E

     

    [KUDOS PLEASE! If you think I earned it!

    If this solution worked for you please flag my post as an "Accepted Solution" so others can benefit..]