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AC87U Asus Merlin - Jumbo Frames and MTU

Discussion in 'Asuswrt-Merlin' started by snbnoob, Sep 11, 2019.

  1. snbnoob

    snbnoob New Around Here

    Joined:
    Sep 27, 2017
    Messages:
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    I'm having an issue setting up Jumbo Frames between my NAS and PC both connected to my AC87U router with the latest Merlin Firmware.

    Both the PC and NAS have 9k frames enabled. The router has Jumbo Frames Enabled as well

    1. When the PC and NAS are connected directly, 9k packets can be sent and received fine, and i get a 5-10% throughput increase vs a lower MTU.
    2. However When the PC and NAS are connected to the router, the max packet caps out at only 3k and performance is lower

    I've tried manually setting the LAN MTU in the router to 9k for all interfaces but this doesnt work either.

    Any idea what is going on here?
     
  2. snbnoob

    snbnoob New Around Here

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    Sep 27, 2017
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    Anyone able to help?
     
  3. netware5

    netware5 Senior Member

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    Location:
    Bulgaria
    You may want to check if ALL LAN devices (not only router, NAS and PC) support jumbo frames and their network interfaces are properly configured. This is a requirement.
     
  4. snbnoob

    snbnoob New Around Here

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    Sep 27, 2017
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    Thanks for your reply, the only devices physically connected to the router are the NAS and PC.

    Would wifi Wii connected devices cause an impact?

    Also if i put the NAS and PC behind a switch and then connect that to the router, all works fine.

    Its only when i plug the NAS and PC directly into the router that jumbo frames and the packet size fails.
     
  5. netware5

    netware5 Senior Member

    Joined:
    Mar 9, 2013
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    366
    Location:
    Bulgaria
    Wi-Fi connected device have no impact. As everything works fine with switch I think you have a problem with router. Did you tried to experiment with different jumbo frames sizes between standard (1.5k) and maximum (9k)? May be the router has a limit for jumbo frame size, i.e. 3k?